Patent Publication Number: US-2023135300-A1

Title: A two-terminal device

Description:
The present invention relates to a two-terminal electronic device. In particular, the two-terminal device may be an optoelectronic device. The present invention also relates to a method of forming a two-terminal electronic device. 
     BACKGROUND 
     A two-terminal device is an electrical component having two terminals, that is, a first terminal and a second terminal. A terminal is generally defined as an area, region or portion of the electrical component that allows the ingress or egress of electrical current to, or from, the electrical component. A two-terminal device includes devices such as a diode, for example a light-emitting diode (LED). A two-terminal device also includes devices such as an optoelectronic device, or photovoltaic device, a transistor, a phototransistor, a vertical-cavity surface-emitting laser (VCSEL), an energy storage device, or the like. As will be recognised by those skilled in the art, these are simply non-exhaustive examples of two-terminal devices. 
     In some examples, such as in optoelectronic technology, otherwise known as photovoltaics, an optoelectronic device produces electricity from light at the junction between two materials that are exposed to the light. Moreover, an optoelectronic device may produce light from the input of electricity. Typically, light used in optoelectronics is sunlight, and therefore photovoltaic is often referred to as solar photovoltaic. It is known to use semiconductors as the two materials. The semiconductor materials used exhibit a photovoltaic effect. 
     The semiconductor materials used are usually a p-type semiconductor material and an n-type semiconductor material. When these semiconductor materials are joined together, they form an interface therebetween often referred to as a p-n junction. Another known interface of semiconductor materials in known as a P-i-N, or PIN, junction. The p-n junction is found in most optoelectronic devices that use semiconductors. These optoelectronic devices include photovoltaic cells, solar photovoltaic cells, diodes, light-emitting diodes (LEDs) and transistors. The p-n junction can be thought of as the active site in which the generation or consumption of electrical energy occurs. 
     The optoelectronic device may be used as a device for generating electricity for immediate use or for storage purposes. Optoelectronic devices that are used for generating electricity for immediate use typically utilise a p-n junction having a semi-conductor therebetween. Optoelectronic devices that are used for generating electricity for storage are regarded as energy storage devices. 
     Existing two-terminal devices, specifically those used in optoelectronic technology, are currently relatively expensive methods of generating electricity. With increasing demands for sources of renewable energy, there is a drive to improve the efficiency of solar photovoltaic cells and to reduce costs associated with the manufacture and running of these devices. Also, existing solar photovoltaic cells remain relatively inefficient in comparison with other methods of generating electricity. 
     In an attempt to overcome such problems, grooved substrates have been developed for two-terminal devices, in particular, photovoltaic devices. A number of series of grooves are provided in parallel to one another, and each series of grooves is then connected in series. Such an example is illustrated in  FIG.  1   , which depicts a prior art device  10  including a first cell  12   a , a second cell  12   b  and a third cell  12   c . The first, second and third cells  12   a ,  12   b ,  12   c  may be photovoltaic cells as shown in  FIG.  1   . In this specific example, the first, second and third cells  12   a ,  12   b ,  12   c  comprise photodiodes. The photodiodes are first connected in parallel to one another, thus forming cells  12   a ,  12   b ,  12   c , and then each photodiode, or each cell  12   a ,  12   b ,  12   c , is connected in series to one another. 
     However, such a configuration provides the disadvantage that, in the event of an unintentional electrical short, a significant impact in the performance of the two-terminal device may be observed. Moreover, in conventional substrates, such as those illustrated in  FIG.  1 ( a ) , a bypass diode (not shown) is typically needed to provide an electrical pathway around one or more of the cells  12   a ,  12   b ,  12   c , in case a portion of the photodiodes are shaded, in use, such that the photodiodes in one or more cells  12   a ,  12   b ,  12   c  cannot convert light energy into electrical energy. That is, when a portion of the device is shaded, one or more cells  12   a ,  12   b ,  12   c  may be non-functional. If a portion of the device is shaded, the performance of the whole substrate is degraded and, in some examples, this may also cause damage to the substrate. Thus, bypass diodes are typically provided to mitigate these disadvantages by providing an alternative current path around any non-functional cells  12   a ,  12   b ,  12   c.    
     One solution to this problem is to use an interdigitated grooved arrangement to connect sections of grooves in parallel with each other. However, such a configuration requires that each cell is to be wired together in series to provide a single module, which is commercially undesirable. 
     In an attempt to provide an improved solution, further grooved substrates for two-terminal devices have been developed. Such grooved substrates provide a number of series of grooves, each groove within a series of grooves being connected in series, and each series of grooves being connected in parallel or in series to one another. The adjacent series of grooves are electrically separated from one another by a delineation feature, such as a channel. The delineation feature typically transects, or intersects, one or more grooves of a first series of grooves at one end of the delineation feature, and one or more grooves of a second series of grooves at the other end of the delineation feature. In this way, once the grooves are coated and filled with appropriate materials to form a two-terminal device, the grooves within a series of grooves are electrically connected in series across the surface of the substrate, thereby allowing voltage addition across the machine direction of the substrate. Thus, by altering the number of grooves in a series of grooves, the output voltage of the two-terminal device can be controlled. 
     Moreover, the delineation feature electrically isolates adjacent series of grooves. First and second terminals of the two-terminal device are provided at opposing sides of the substrate, arranged to extract charge from each series of grooves. The first terminal is electrically connected to a first groove of a series of grooves and the second terminal in electrically connected to a last groove of the same series, 
     Whilst such two-terminal devices having grooved substrates tend to be more efficient and less expensive to manufacture than other known two-terminal devices, such grooved substrates can be prone to manufacturing defects. In particular, during the manufacture of such grooved devices, the grooves are filled so that an electrical connection can be provided between each groove within a series of grooves. However, if such a step is carried out after the formation of the grooves the filling material also collects in the delineation feature, such as a channel. Oftentimes, unintentional collection of filling material in a channel occurs to such an extent that an electrical connection is provided across it, thus electrically connecting the adjacent series of grooves and causing an electrical short. This was previously thought of as being highly undesirable, as the efficiency of the device is often dramatically reduced. In an attempt to overcome such a problem, manufactures seek to mediate the amount of filling material collected within the delineation feature. However, this can be time consuming, expensive and, oftentimes, unsuccessful. 
     However, much to the surprise of the present inventors, it has been found that not only is it possible to commercially manufacture two-terminal devices having an electrical connection between adjacent parallel or series-connected cells, but in fact there are advantages of such two-terminal devices, as described further herein. 
     Therefore, it is an aim of the present invention to provide a two-terminal device that mitigates at least one or more of the aforementioned problems. 
     SUMMARY OF INVENTION 
     As used herein, the term “cell” is used to describe a component that provides electrical energy, and in particular converts one type of energy, for example light, chemical or the like, into electrical energy. The cell may include one or more grooves, optionally provided as series of grooves, as described herein. The cell may also include one or more connecting portion between grooves or series of grooves, as well as means to extract electrical charge from the grooves. 
     As used herein, the term “groove” is used to describe a depression, an indentation, an etch or the like in a substrate. The groove generally includes an elongated length, a width and a depth. The groove may be coated on its first and second face, and filled with a material, thereby providing an appropriate cell. 
     As used herein, the term “resistive element” is used to describe an element having a resistance. The resistance of the resistive element contributes to the third characteristic resistance. For example, a resistive element may impart an increased resistance to the connecting portion. 
     As used herein, the term “channel” is used to describe an example of a resistive element. The channel may take the form of a depression, an indentation, an etch or the like in a substrate. The channel generally includes an elongated length, a width and a depth, the width or the depth being greater than a depth of a groove. 
     As used herein, the term “aspect ratio” is used to describe a ratio between width and depth of a feature. The aspect ratio is presented as width:depth or width/depth. 
     In accordance with one aspect of the present invention, there is provided a two-terminal device, including a substrate comprising: 
     a first cell having a first characteristic resistance, and a second cell, spaced apart from the first cell along the web direction of the substrate, having a second characteristic resistance; 
     a first terminal and a second terminal, each terminal being formed towards or at opposing edges of the substrate across the transverse direction, and each terminal being in electrical communication with the first cell and the second cell; 
     a connecting portion, between the first cell and the second cell, the connecting portion having a third characteristic resistance; 
     wherein the third characteristic resistance is greater than or equal to at least one of the first characteristic resistance and the second characteristic resistance, such that an electrical charge from the first or second cell is extractable at the first terminal or the second terminal in preference to transferring between the first cell and the second cell across the connecting portion. 
     The two-terminal device may be any appropriate device having a first terminal and a second terminal. The two-terminal device may be an optoelectronic device. An optoelectronic device may be defined as a device that converts light energy into electrical energy and/or that converts electrical energy into light energy. The term light energy is used generally to define any wavelength of light within the electromagnetic spectrum. In some examples, the light energy may include UV light, visible light and/or infrared light. In some examples, the light energy may include electromagnetic radiation having a wavelength from 10 nm to 1 mm. 
     The substrate can be a flexible substrate. The flexible substrate can be composed of a web of flexible material. The substrate may have a transverse direction, that is a direction across the width of the substrate, and a web direction, that is a direction across an elongate length of the substrate. The web direction may be regarded as a longitudinal or a machine direction. The substrate may have a predetermined length, in the web direction, a predetermined width, in the transverse direction, and a predetermined depth. 
     The flexible substrate may be provided as a length of continuous flexible substrate. In some examples, the length of continuous flexible substrate is provided on a roll or a roll core. This provides roll-to-roll continuous manufacture, which provides a more cost and labour efficient manufacturing process. In some particular examples, the length of continuous flexible substrate is up to 6000 m, that is less than or equal to 6000 m. 
     The first cell and the second cell may be any appropriate electrical cell, that is, a device that is capable of converting one form of energy into electricity or electrical energy. The first cell and the second cell may be, independently, an optoelectronic cell, such as a solar photovoltaic cell. Alternatively, the first cell and the second cell may be, independently, a capacitor or a battery. The first cell, the second cell or both the first and second cell may include one or more grooves or series of grooves. Any combination thereof may be contemplated. The first cell and the second cell may be spaced apart along the web direction of the substrate or along the transverse direction of the substrate. The first terminal and the second terminal may be formed towards or at opposing edges of the substrate across the transverse direction, or may be formed across the web direction. 
     In some examples, the connecting portion may be formed across substantially all of, or all of, the region between the first cell and the second cell. That is, in some examples, the connecting portion may connect the first cell to the second cell along the web direction of the substrate. The connecting portion may provide electrical connectivity between the first cell and the second cell. Alternatively, the connecting portion may prevent electrical connectivity between the first cell and the second cell. In some examples, although the connecting portion may provide electrical connectivity between the first cell and the second cell, electrical charge preferably flows to the first terminal and the second terminal. That is, electrical charge is extracted or the like, in use, at the first terminal and the second terminal in preference to electrical charge transferring between the first cell and the second cell. This preference is generally a function of the third characteristic resistance with respect to the first characteristic resistance, the second characteristic resistance or both the first characteristic resistance and the second characteristic resistance. 
     Surprisingly, the inventors have found that the connecting portion, in particular resistive elements therein, acts as a reverse-biased diode in parallel with a resistor. In this way, although an electrical pathway is provided across the connecting portion, electrical charge from a cell is extractable at the terminals in preference to electrical charge transfer across the connecting portion. 
     The term characteristic resistance is used to define the resistance as a function of the voltage divided by the current at the maximum power point. The characteristic resistance may be defined as: 
     
       
         
           
             
               R 
               Characteristic 
             
             = 
             
               
                 V 
                 
                   Maximum 
                   ⁢ 
                      
                   Power 
                 
               
               
                 I 
                 
                   Maximum 
                   ⁢ 
                      
                   Power 
                 
               
             
           
         
       
     
     This provides the advantage that electrical shorts between the first cell and the second cell are prevented. In particular, manufacturing defects, such as the creation of electrical shorts between the first cell and the second cell, may be minimised. More particularly, since the third characteristic resistance is provided such that electrical charge is still extractable at the terminals, an improved manufacturing process may be provided, in which less attention may be taken to avoid creating electrical shorts during the manufacturing process. That is, providing the connecting portion to electrically connect the first and second cells may ensure that electrical shorts between the first cell and the second cell are prevented without the need for a user to intervene during the manufacturing process. Thus, a more efficient and/or reliable two-terminal device may be formed. 
     In certain embodiments, the third characteristic resistance is greater than at least one of the first characteristic resistance and the second characteristic resistance. 
     That is, the third characteristic resistance may be greater than the first characteristic resistance, the second characteristic resistance, or both the first and the second characteristic resistance. 
     In certain embodiments, the third characteristic resistance is at least two times, preferably at least five times, most preferably at least ten times, greater than at least one of the first characteristic resistance and the second characteristic resistance. 
     In some examples, the third characteristic resistance is from two times to one hundred times greater than at least one of the first characteristic resistance and the second characteristic resistance. In some examples, the third characteristic resistance is from two times to twenty times greater than at least one of the first characteristic resistance and the second characteristic resistance. In some examples, the third characteristic resistance is from five times to ten times greater than at least one of the first characteristic resistance and the second characteristic resistance. Any combination of ranges is contemplated herein. For example, the third characteristic resistance may be from two times, five times, ten times, or twenty times to five times, ten times, twenty times, or fifty times greater than at least one of the first characteristic resistance and the second characteristic resistance. Any integer therebetween is also contemplated. Moreover, the third characteristic resistance may be two times, five times, ten times, twenty times, fifty times or one hundred times greater than at least one of the first characteristic resistance and the second characteristic resistance. 
     That is, the third characteristic resistance may be at least two times greater than the first characteristic resistance, the second characteristic resistance, or both the first and the second characteristic resistance. In some examples, it may be preferable that the third characteristic resistance may be five times greater than the first characteristic resistance, the second characteristic resistance, or both the first and the second characteristic resistance. In some examples, it may be preferable that the third characteristic resistance may be ten times greater than the first characteristic resistance, the second characteristic resistance, or both the first and the second characteristic resistance. In some examples, it may be preferable that the third characteristic resistance may be twenty times greater than the first characteristic resistance, the second characteristic resistance, or both the first and the second characteristic resistance. In some examples, it may be preferable that the third characteristic resistance may be fifty times greater than the first characteristic resistance, the second characteristic resistance, or both the first and the second characteristic resistance. In some examples, it may be preferable that the third characteristic resistance may be one hundred times greater than the first characteristic resistance, the second characteristic resistance, or both the first and the second characteristic resistance. 
     This provides the advantage that the likelihood of providing an electrical short across the connecting portion during manufacturing is minimised. Thus, the performance of the two-terminal device may be improved. In particular, the two-terminal device may have a better efficiency and/or reliability. 
     In certain embodiments, the connecting portion comprises at least one resistive element. 
     That is, the substrate may comprise at least one resistive element between the first cell and the second cell, within the connecting portion. 
     In some embodiments, the at least one resistive element provides substantially some of, most of, or all of the third characteristic resistance. In some embodiments, each resistive element, in combination, provides substantially some of, most of, or all of the third characteristic resistance. 
     In some embodiments, an electron transfer path may be formed across the, or each of, or some of, the resistive element or elements within the connecting portion. In some embodiments, the electron transfer path is formed from between the first cell and the second cell across the, or each of, or all of, the resistive element or elements within the connecting portion. 
     This provides the advantage that the third characteristic resistance can be modified as a function of structural properties of the at least one resistive element. For example, the third characteristic resistance can be modified as a function of the number, the size of, the structure, or the like, of the at least one resistance element. That is, the third characteristic resistance can be tuned as a function of the at least one resistive element. 
     In certain embodiments, the at least one resistive element comprises a peak of the substrate, a discontinuous non-insulating coating of the substrate, and/or a rutted portion of the substrate. 
     That is, in certain embodiments, the at least one resistive element may comprise, may include or may be one or more peaks of the substrate, that is, one or more projections, protrusions or the like formed in the substrate. 
     Alternatively, or additionally, the at least one resistive element may comprise, may include or may be a discontinuous non-insulating coating of the substrate. That is, a non-insulating coating may be deposited on the substrate to provide one or more resistive elements. The non-insulating coating may be discontinuous in that there is discontinuity across the substrate in the web direction. The discontinuous non-insulating coating may be formed by etching, or removing, a portion of another coating of the substrate to expose a non-insulating coating. The non-insulating coating may be discontinuous in that there is discontinuity across the substrate in the web direction. In some embodiments, the discontinuous non-insulating coating may be formed by masking of a region of the connecting portion during manufacture. Thus, a region of the connecting portion may be devoid of conductive material. 
     Alternatively, or additionally, the at least one resistive element may comprise, may include or may be a rutted portion of the substrate. That is, in certain embodiments, the connecting portion may have one or more rutted portions or regions. A rutted-portion may be defined as a jagged, uneven, undulated surface or the like. 
     In certain embodiments, the at least one resistive element comprises a channel in the substrate. 
     That is, the at least one resistive element may comprise, may include or may be formed as a channel in the substrate. A channel may be regarded as an indentation or etch or the like in the substrate. 
     This provides the advantage that the first cell and the second cell may be, or may substantially be, electrically separated from one another. In other words, the first cell and second cell are connected in series across the third characteristic resistance. 
     In certain embodiments, the channel comprises a rutted-base, a rutted-wall and/or a non-conductive electrical insulator material therein. 
     That is, in some examples, the channel may include a rutted-bottom or a rutted-base. That is, the bottom, or the base, of the channel may be rutted in that the bottom, or the base, is jagged, uneven, undulated or the like. 
     Additionally or alternatively, the channel may include a rutted-wall. That is, the wall of the channel may be rutted in that the wall is jagged, uneven, undulated or the like. 
     This provides the advantage that the electron transfer path between the first cell and the second cell may be increased, thus increasing the third characteristic resistance and preventing the creation of electrical shorts during the manufacturing process. Furthermore, the third characteristic resistance can be modified as a function of structural properties of the rutted-wall or rutted-bottom. For example, the third characteristic resistance can be modified as a function of the number, the size of, the structure, or the like, of the rutted-wall or the rutted-bottom. That is, the third characteristic resistance can be tuned as a function of the rutted-wall or rutted-bottom. 
     Additionally or alternatively, the channel may include a non-conductive electrical insulator material within the channel. The non-conductive electrical insulator may partially, mostly, or entirely fill the channel. 
     This provides the advantage that the electron transfer path between the first cell and the second cell may be increased, thus increasing the third characteristic resistance and preventing the creation of electrical shorts during the manufacturing process. Furthermore, the third characteristic resistance can be modified as a function of structural properties of the non-conductive electrical insulator material. For example, the third characteristic resistance can be modified as a function of the amount, the size, the structure, or the like, of the non-conductive electrical insulator material. That is, the third characteristic resistance can be tuned as a function of the non-conductive electrical insulator material. 
     In certain embodiments, the channel has an aspect ratio of at least 1:1.6. 
     That is, in certain embodiments, the channel has an aspect ratio that may be 1:1.6 or greater than 1:1.6, for example, 1:1.8, 1:1.9, 1:2.0 or the like. The term aspect ratio is used to define a ratio between the width and the depth. Thus, an aspect ratio of at least 1:1.6 may be regarded as a ratio of 1:1.6, referring to the width:depth of the channel, or greater. That is, the depth of the channel may be greater than the width of the channel. 
     This provides the advantage that the electron transfer path, from the first cell to the second cell, is lengthened, thus increasing the third characteristic resistance of the substrate. Thus, the third characteristic resistance of the substrate may be tuned. 
     In certain embodiments, the channel has an aspect ratio of at least 1.6:1. 
     This provides the advantage that the electron transfer path, across the width of the channel, is increased, thus reducing the likelihood that an electron may “hop” across the gap formed by the channel. 
     In certain embodiments, the first cell comprises at least one first groove and/or the second cell comprises at least one second groove. 
     That is, in certain embodiments, the first cell comprises at least one groove, or at least one first groove, the second cell comprises at least one groove, or at least one second groove, or the first cell comprises at least one groove, or at least one first groove, and the second cell comprises at least one groove, or at least one second groove. 
     The term “groove” may be used to define a depression, an indentation, an etch or the like in the substrate. The or each groove may differ to a channel in depth or aspect ratio. For example, a groove may have a depth that is smaller than a channel. For example, a groove may have an aspect ratio of approximately 1:1 or 1:1.1 or 1:1.2 or no greater than 1:1.2 or at least 1:1.2. For example, a groove may have an aspect ratio that is smaller than an aspect ratio of the channel. 
     In some examples, the at least one groove may comprise a single groove having parallel sections adjoined at opposing edges, thereby forming a substantially repeating S-shape. 
     This provides the advantage that the current of the two-terminal device may be controlled by the length of the at least one first groove and/or the length of the at least one second groove. In particular, voltage addition may occur along the web direction of the at least one first and/or second groove. Thus, by increasing or decreasing the length of the at least one first and/or second groove, the output voltage of the two-terminal device may be controlled. Thus, this may provide the advantage that the two-terminal device is tuneable. 
     In certain embodiments, the channel transects a portion of the at least one first groove and/or the at least one second groove. 
     That is, the channel may transect, or intersect, one part or portion of, some of, most of, or all of the at least one first groove, the at least one second groove, or both the at least one first groove and the at least one second groove. 
     This provides the advantage that the at least one first and/or second groove is electrically connected across the web direction, thus allowing for voltage addition, whilst electrically isolating the at least one first groove (i.e. the first cell) from the at least one second groove (i.e. the second cell). 
     In certain embodiments, the first cell comprises at least one first groove and/or the second cell comprises at least one second groove, and the channel transects a portion of the at least one first groove and/or a portion of the at least one second groove. 
     That is, in certain embodiments, the first cell comprises at least one groove, the second cell comprises at least one second groove, or both the first cell comprises at least one first groove and the second cell comprises at least one second groove. Further, in certain embodiments, the channel transects a portion of the at least one first groove, a portion of the at least one second groove, or both a portion of the at least one first groove and a portion of the at least one second groove. The channel may transect some of, part of, most of, or all of the at least one first groove and/or the at least one second groove. 
     In certain embodiments, the first cell comprises a first series of grooves and/or the second cell comprises a second series of grooves. 
     That is, in certain embodiments, the first cell comprises a first series of grooves, the second cell comprises a second series of grooves, or the first cell comprises a first series of grooves and the second cell comprises a second series of grooves. 
     The first series of grooves comprises any number of grooves, and may include a first terminal groove and a second terminal groove. Each groove of the first series of grooves may extend across the transverse direction of the substrate. Each groove of the first series of grooves may extend in parallel. Any number of grooves may be provided within the first series of grooves between a first terminal groove and a second terminal groove. The first terminal groove may terminate, or form a terminus of, the first series of grooves at one end, or a first end, for example a distal end. The second terminal groove may terminate, or form a terminus of, the first series of grooves at another end, or a second end, for example a proximal end. The distal end and the proximal end denote ends of the first series of grooves across the web direction of the substrate. 
     The second series of grooves comprises any number of grooves, and may include a first terminal groove and a second terminal groove. Each groove of the second series of grooves may extend across the transverse direction of the substrate. Each groove of the second series of grooves may extend in parallel. Each groove of the second series of grooves may be in parallel with each groove of the first series of grooves. Any number of grooves may be provided within the second series of grooves between a first terminal groove and a second terminal groove. The first terminal groove may terminate, or form a terminus of, the second series of grooves at one end, or a first end, for example a distal end. The second terminal groove may terminate, or form a terminus of, the second series of grooves at another end, or a second end, for example a proximal end. The distal end and the proximal end denote ends of the second series of grooves across the web direction of the substrate. The first terminal groove and the second terminal groove may each be proximal to the connecting portion of the substrate. 
     The second terminal groove of the first series of grooves and the first terminal of the second series of grooves may be separated by, or spaced apart by, the connecting portion. That is, there may exist a connecting portion between the first series of grooves and the second series of grooves. 
     The first series of grooves and the second series of grooves may have a first characteristic resistance and a second characteristic resistance, respectively. The third characteristic resistance may be greater than the first characteristic resistance, the second characteristic resistance, or both the first and the second characteristic resistance. The third characteristic resistance may be equal to, or substantially equal to, the first characteristic resistance the second characteristic resistance, or both the first and the second characteristic resistance. 
     In some embodiments, the at least one first groove and/or the at least one second groove may be coated with a first material on a first face, may be coated with a second material on a second face and/or may be at least partially, preferably mostly or entirely, filled with a third material. 
     That is, a first face of the at least one first groove and/or the at least one second groove, is coated with a first material. That is, a second face of the at least one first groove and/or the at least one second groove is coated with a second material. That is, the at least one first groove and/or the at least one second groove, are at least partially filled with a third material. In certain embodiments, the groove or grooves in question are filled with a third material to the extent that the third material contacts the first material and/or the second material deposited on the first face and/or the second face. 
     In some embodiments, a portion of the first series of grooves and/or a portion of the second series of grooves may be coated with a first material on a first face, may be coated with a second material on a second face and/or may be at least partially, preferably mostly or entirely, filled with a third material. 
     That is, a first face of a portion, preferably most of or all of, the first series of grooves and/or the second series of grooves is coated with a first material. That is, a second face of a portion, preferably most of or all of, the first series of grooves and/or the second series of grooves is coated with a second material. That is, a portion, preferably most of or all of, the first series of grooves and/or the second series of grooves are at least partially filled with a third material. In certain embodiments, the groove or grooves in question are filled with a third material to the extent that the third material contacts the first material and/or the second material deposited on the first face and/or the second face. 
     In certain embodiments, the first face and/or the second face of the respective groove or grooves are coated with the first material and/or the second material by an off-axis directional coating process. 
     This provides the advantage that certain faces of the groove or grooves can be selectively coated during manufacture. 
     In certain embodiments, the respective groove or grooves are at least partially filled by printing a third material onto the substrate. 
     This provide the advantage that the two-terminal device can be manufactured more efficiently. 
     In certain embodiments, the first material comprises a non-insulating material. 
     In some embodiments, the first material comprises a conductor material, a semiconductor material, an electron transfer layer, carbon-60 (C 60 , also known as Buckminsterfullerene), or a combination thereof. In some examples, there may be a plurality of materials. That is, there may be at least one first material. In some examples, the semiconductor material comprises a metal oxide. In some examples, the metal oxide comprises niobium oxide, that is Nb 2 O 5 , or tin oxide, that is tin (IV) oxide, SnO 2 . The metal oxide may be doped with an appropriate material. 
     In certain embodiments, the second material comprises a non-insulating material. 
     In some embodiments, the second material comprises a conductor material, a semiconductor material, a hole transport layer, or a combination thereof. In some examples, there may be a plurality of materials. That is, there may be at least one second material. In some examples, the semiconductor material comprises a metal oxide. In some examples, the metal oxide comprises nickel oxide, that is nickel (II) oxide or NiO, or copper oxide, that is copper (I) oxide, Cu 2 O. The metal oxide may be doped with an appropriate material. 
     In certain embodiments, the third material comprises a capacitor material, a supercapacitor material, a dielectric material or a perovskite structured material. 
     It may be preferable that the third material comprises a perovskite structured material. A perovskite structured material is a material having a crystal structure corresponding to calcium titanium oxide, CaTiO 3  that is, having a general chemical structure of ABX 3 , for example  XII A 2+ VI B 4+ X 2−   3 , where A and B are two different cations of different sizes, and X is an anion that chemically bonds to both A and B. 
     In preferred examples, the perovskite structured material has an optical bandgap between 1.1 eV and 2.5 eV. 
     In preferred examples, the perovskite structured material comprises an organic lead trihalide, such as methylammonium lead trichloride, tribromide or triiodide, formamidinium lead trihalide, such as formamidinium lead trichloride, tribromide or triiodide, caesium tin trihalide, such as caesium tin triiodide, or another like organic lead or tin halide combination with the general chemical structure of ABX 3  as outlined above. 
     Perovskites are generally earth abundant and thus are inexpensive. Furthermore, perovskites are suitable for low temperature processing and manufacturing, and are also suitable for solution processing, thereby providing manufacturing benefits. Moreover, perovskites are generally highly efficient in terms of converting light energy into electrical energy. 
     Any combination of the first material, the second material and the third material is contemplated herein. 
     In certain embodiments, the channel transects a portion of the first series of grooves and/or a portion of the second series of grooves. 
     That is, in certain embodiments in which there is at least one resistive element comprising a channel, the channel transects, or intersects or cuts across or the like, a portion, that is one of, some of, most of or all of, the first series of grooves, the second series of grooves, or both the first series of grooves and the second series of grooves. 
     In certain embodiments, the first cell comprises a first series of grooves and/or the second cell comprises a second series of grooves, wherein the channel transects a portion of the first series of grooves and/or a portion of the second series of grooves. 
     That is, in certain embodiments in which there is at least one resistive element comprising a channel, the channel transects, or intersects or cuts across or the like, a portion, that is one of, some of, most of or all of, the at least one first groove, the at least one second groove, or both the at least one first groove and the at least one second groove. 
     This provides the advantage that the portion of the first series of grooves and/or the portion of the second series of grooves is or are electrically connected across the web direction, thus allowing for voltage addition, whilst electrically isolating each series of grooves (i.e. the first cell and the second cell). 
     In certain embodiments, the channel transects the entirety of the first series of grooves and/or the entirety of the second series of grooves. 
     That is, in certain embodiments, the channel transects the entirety of, that is all of or each and every one of, the first series of grooves, the second series of grooves or both the first series of grooves and the second series of grooves. 
     In certain embodiments, the channel transects the first series of grooves and/or the second series of grooves towards an end of each groove. 
     That is, in certain embodiments in which there is at least one resistive element comprising a channel, the channel transects the first series of grooves, the second series of grooves, or both the first series of grooves and the second series of grooves, towards an end of each groove. In some examples, the channel transects the first series of grooves, the second series of grooves, or both the first series of grooves and the second series of grooves, at an end of each groove. In some examples, the channel transects the groove or grooves of the first series of grooves towards a proximal end of the respective groove or grooves, and the channel transects the groove or grooves of the second series of grooves towards a distal end of the respective groove or grooves. 
     In certain embodiments, the channel is substantially Z-shaped having a predetermined angle. 
     That is, the channel may form a substantial Z-shape, for example, when viewed from above. The Z-shaped channel may comprise a first region and a second region extending substantially in parallel. The first and second channel regions may extend along the web direction of the substrate. The first channel region may transect a portion of the first series of grooves. The second channel region may transect a portion of the second series of grooves. The channel forming a substantial Z-shape may further comprise a third region extending from one end of the first region to one end of the second region. The third region may extend in the web direction of the substrate. A first predetermined angle may be formed between the first region and the third region. A second predetermined angle may be formed between the second region and the third region. The first predetermined angle may be equal to the second predetermined angle. In such cases, the Z-shaped channel may be regarded as having a predetermined angle. Alternatively, the first predetermined angle may not be equal to the second predetermined angle, in which case the Z-shaped channel may be regarded as having a first predetermined angle and a second predetermined angle. 
     In some embodiments, the predetermined angle is, or the first and the second predetermined angles independently are, in the range of 0 degrees to 90 degrees, excluding 0 degrees and excluding 90 degrees. In some embodiments, the predetermined angle is, or the first and second predetermined angles are, in the range of 0 degrees to 180 degrees, excluding 0 degrees and 180 degrees. In some embodiments, the predetermined angle is, or the first and the second predetermined angles independently are, between 0 degrees and 90 degrees, that is, excluding 0 degrees and 90 degrees. In some embodiments, the predetermined angle is, or the first and the second predetermined angles independently are, in the range of 30 degrees to 60 degrees, including 30 degrees or 60 degrees or including 30 degrees and 60 degrees. In some embodiments, the predetermined angle is, or the first and the second predetermined angles independently are, between 30 degrees and 60 degrees, that is excluding 30 degrees and 60 degrees. In some embodiments, the predetermined angle is, or the first and the second predetermined angles independently are, in the range of 40 degrees to 50 degrees, including 40 degrees or 50 degrees or including 40 degrees and 50 degrees. In some embodiments, the predetermined angle is, or the first and the second predetermined angles independently are, between 40 degrees and 50 degrees, that is excluding 40 degrees and 50 degrees. It may be preferable that the predetermined angle is, or the first and the second predetermined angles independently are, approximately 45 degrees 
     In some embodiments, the predetermined angle, or the first and the second predetermined angles independently, may have a lower limit of 1 degree, 5 degrees, 10 degrees, 15 degrees, 20 degrees, 25 degrees, 30 degrees, 35 degrees, 40 degrees, 45 degrees, 50 degrees, 55 degrees, 60 degrees, 65 degrees, 70 degrees, 75 degrees, 80 degrees, 85 degrees, 90 degrees, 95 degrees, 100 degrees, 105 degrees, 110 degrees, 115 degrees, 120 degrees, 125 degrees, 130 degrees, 135 degrees, 140 degrees, 145 degrees, 150 degrees, 155 degrees, 160 degrees, 165 degrees, 170 degrees, 175 degrees, or any integer therebetween. The upper limit of the predetermined angle, or the first and the second predetermined angles independently, may be 5 degrees, 10 degrees, 15 degrees, 20 degrees, 25 degrees, 30 degrees, 35 degrees, 40 degrees, 45 degrees, 50 degrees, 55 degrees, 60 degrees, 65 degrees, 70 degrees, 75 degrees, 80 degrees, 85 degrees, 90 degrees, 95 degrees, 100 degrees, 105 degrees, 110 degrees, 115 degrees, 120 degrees, 125 degrees, 130 degrees, 135 degrees, 140 degrees, 145 degrees, 150 degrees, 155 degrees, 160 degrees, 165 degrees, 170 degrees, 175 degrees, 179 degrees or any integer therebetween. As will be recognised by the person skilled in the art, any combination of lower limit and upper limit may be used. 
     In other embodiments, the predetermined angle, or the first and the second predetermined angles independently, may have an upper limit of greater than 90 degrees. 
     During the manufacture of two-terminal devices, an off-axis directional coating process is often used, in which one face of the grooves, and the delineation feature, is selectively coated. This is particularly useful for roll-to-roll manufacture of such two-terminal devices, as the manufacturing process can be carried out as a continuous process, rather than batch process. In such cases, the opposing face of the grooves casts a shadow onto the face to be coated, such that only a portion of the face to be coated can be coated by the incoming material. This is known as the “shadowing effect”. Thus, the shadowing effect governs the amount of material deposited on a face of the grooves. The shadowing effect can be modified by increasing or decreasing the angle of the off-axis directional coating. 
     The Z-shaped channel provides the advantage that the shadowing effect, during manufacture of two-terminal devices using such substrates, is increased, thus less material is coated at the interface between a series of grooves and a channel. Thus, the characteristic resistance of the channel, and thus the third characteristic resistance of the substrate, may be increased during the manufacturing process. This may provide the advantage that electrical shorts are prevented across the channel, and thus between the first cell and the second cell. 
     In certain embodiments, the at least one resistive element comprises a plurality of channels in the substrate. 
     That is, the at least one resistive element may comprise, may include, or may be formed by, one, more than one, or two or more, or a multiple, or a plurality, of channels in the substrate. A channel may be formed as an indentation or etch or the like in the substrate. The resistive element may comprise a channel and another type of resistive element as described herein, for example, a non-conductive electrical insulating material, a rutted-bottom or rutted-wall of the channel, or the like. 
     This provides the advantage that if there is an electrical short across one channel, for example created during manufacturing, another channel is present to prevent electrical connection between the first cell and the second cell. Thus, redundancy is provided by way of multiple of resistive elements in the event that one unintentionally provides an electrical short thereacross. Thus, the likelihood of an electrical short being created during manufacture may be reduced. Thus, this may provide the advantage that a more efficient and/or reliable two-terminal device may be provided. 
     In certain embodiments, one or more of the plurality of channels comprises a rutted-base, a rutted-wall and/or a non-conductive electrical insulator material therein. 
     In certain embodiments, one of, some of, most of, or all of the plurality of channels includes a rutted-based, or a rutted-wall, or a non-conductive electrical insulator material therein, or any combination thereof. 
     In some examples, one of, some of, most of, or all of the plurality of channels may include a rutted-bottom or a rutted-base. That is, the bottom, or the base, of one of, some of, most of, or all of the plurality of channels may be rutted. More specifically, the bottom, or the base, is jagged, uneven, undulated or the like. 
     Additionally or alternatively one of, some of, most of, or all of the plurality of channels may include a rutted-wall. That is, the wall of one of, some of, most of, or all of the plurality of channels may be rutted in that the wall is jagged, uneven, undulated or the like. 
     Additionally or alternatively, one of, some of, most of, or all of the plurality of channels may include a non-conductive electrical insulator material within the channel. The non-conductive electrical insulator may partially, mostly, or entirely fill one of, some of, most of, or all of the plurality of channels 
     This provides the advantage that the resistance of the, or each, channel, and thus the third characteristic resistance, is increased thereby reducing the likelihood of an electrical short being formed between the first cell and the second cell. Furthermore, the third characteristic resistance may be tuned based upon the number and type of resistive elements formed as part of, or within, the or each channel. 
     In certain embodiments, one or more of the plurality of channels has an aspect ratio of at least 1:1.6. 
     That is, in certain embodiments, one of, some of, most of, or all of the plurality of channels may have an aspect ratio that may be 1:1.6 or greater than 1:1.6, for example, 1:1.8, 1:1.9, 1:2.0 or the like. The term aspect ratio is used to define a ratio between the width and the depth. Thus, an aspect ratio of at least 1:1.6 may be regarded as a ratio of 1:1.6, referring to the width:depth of one of, some of, most of, or all of the plurality of channels, or greater. That is, the depth of one of, some of, most of, or all of the plurality of channels may be greater than the width of the respective channel. 
     This provides the advantage that, as the aspect ratio increases, the electron transfer path between the first cell and the second cell increases. That is, the electron transfer path between the first cell and the second cell increases as a function of the aspect ratio of the channel or channels. In this way, the third characteristic resistance increases as a function of the aspect ratio of the channel or channels. In this way, the third characteristic resistance may be modified, or tuned, as a function of the aspect ratio of the channel or channels. 
     In certain embodiments, one or more of the plurality of channels has an aspect ratio of at least 1.6:1. 
     In certain embodiments, one of, some of, most of, or all of the plurality of channels may have an aspect ratio that may be 1.6:1 or greater than 1.6:1, for example, 1.8:1, 1.9:1, 2.0:1 or the like. The term aspect ratio is used to define a ratio between the width and the depth. Thus, an aspect ratio of at least 1.6:1 may be regarded as a ratio of 1.6:1, referring to the width:depth of one of, some of, most of, or all of the plurality of channels, or greater. That is, the width of one of, some of, most of, or all of the plurality of channels may be greater than the depth of the respective channel. 
     This provides the advantage that, as the aspect ratio increases, the electron transfer path between the first cell and the second cell increases. That is, the electron transfer path between the first cell and the second cell increases as a function of the aspect ratio of the channel or channels. In this way, the third characteristic resistance increases as a function of the aspect ratio of the channel or channels. In this way, the third characteristic resistance may be modified, or tuned, as a function of the aspect ratio of the channel or channels. In certain embodiments, the first cell comprises at least one first groove and/or the second cell comprises at least one second groove, and each channel transects the at least one first groove and/or the at least one second groove. 
     In certain embodiments, the first cell comprises at least one first groove, the second cell comprises at least one second groove, or both the first cell comprises at least one first groove and the second cell comprises at least one second groove. Further, in certain embodiments, more than one, some, most, each or all of the channels transect the at least one first groove, the at least one second groove or both the at least one first groove and the at least one second groove. 
     This provides the advantage that the third characteristic resistance is tuneable, in addition to redundancy being built into the connecting portion such that electrical shorts between the first cell and the second cell are prevented, even in the event that one of the channels fails in its electrical isolation. Furthermore, such an arrangement may prevent electrical shorts across a transection region between grooves and the terminals. That is, the channel may transect the grooves such that electrical isolation between a series of grooves and an adjacent terminal is achieved. Thus, a more efficient and/or reliable two-terminal device may be provided. 
     In certain embodiments, the first cell comprises a first series of grooves and/or the second cell comprises a second series of grooves, and each channel transects a portion of the first series of grooves and/or a portion of the second series of grooves. 
     In certain embodiments, the first cell comprises a first series of grooves, the second cell comprises a second series of grooves, or both the first cell comprises a first series of grooves and the second cell comprises a second series of grooves. As discussed above, the first and second series of grooves may have any number of grooves and may have terminal grooves. Further, in certain embodiments, more than one, some, most, each or all of the channels transect a portion, that is one, some, most, or all, of the first series of grooves, the second series of grooves or both the first series of grooves and the second series of grooves. Each channel may transect the entirety of the first series of grooves and/or the second series of grooves. 
     This provides the advantage that the third characteristic resistance is tuneable, in addition to redundancy being built into the connecting portion such that electrical shorts between the first cell and the second cell are prevent, even in the event that one of the channels fails in its electrical isolation. Furthermore, such an arrangement may prevent electrical shorts across a transection region between grooves and the terminals. That is, the channel may transect the grooves such that electrical isolation between a series of grooves and an adjacent terminal is achieved. Thus, a more efficient and/or reliable two-terminal device may be provided. 
     In certain embodiments, each channel transects the first series of grooves and/or the second series of grooves towards an end of each groove. 
     In certain embodiments, each channel, that is more than one, some, most or all of the channels, transects the first series of grooves, the second series of grooves, or both the first series of grooves and the second series of grooves towards an end of each respective transected groove. In some examples, each channel transects the first series of grooves and/or the second series of grooves at an end of each groove. 
     In certain embodiments, the plurality of channels comprises a first channel, having a first channel characteristic resistance, and a second channel, having a second channel characteristic resistance, wherein the first channel characteristic resistance and the second channel characteristic resistance provide substantially all of the third characteristic resistance. 
     That is, in certain embodiments, the plurality of channels comprises a first channel and a second channel. The first channel may have a first channel characteristic resistance. The second channel may have a second channel characteristic resistance. The first channel characteristic resistance and the second channel characteristic resistance, that is, a combination thereof, may provide substantially all, or all, of the third characteristic resistance. 
     This provides the advantage that the third characteristic resistance may be tuneable according to the characteristic resistances of the first and second channel. 
     In certain embodiments, the plurality of channels further comprises a third channel, having a third channel characteristic resistance, wherein the first channel characteristic resistance, the second channel characteristic resistance and the third channel characteristic resistance provide substantially all of the third characteristic resistance. 
     In certain embodiments, the plurality of channels comprise a first channel, a second channel and a third channel. The first channel may have a first channel characteristic resistance. The second channel may have a second channel characteristic resistance. The third channel may have a third channel characteristic resistance. The first channel characteristic resistance, the second channel characteristic resistance, and the third channel characteristic resistance that is, a combination thereof, may provide substantially all, or all, of the third characteristic resistance. 
     This provides the advantage that the third characteristic resistance can be further tuned by providing a further channel. Furthermore, the third characteristic resistance may be increased by providing an additional channel. 
     In certain embodiments, the channel, or each channel of the plurality of channels, is substantially Z-shaped having a predetermined angle. 
     In certain embodiments, each channel of the plurality of channels is substantially Z-shaped having a predetermined angle. 
     The Z-shaped channel or channels may include any of the features described above in relation to Z-shaped channels. 
     In certain embodiments, the two-terminal device further comprises: 
     a first transection channel that transects each channel of the plurality of channels at their distal ends and transects the at least one first groove; 
     a second transection channel that transects each channel of the plurality of channels at their proximal ends and transects the at least one second groove. 
     That is, in certain embodiments, the first cell comprises at least one first groove and the second cell comprises at least one second groove, and the substrate further comprises a first transection channel that transects each channel of the plurality of channels at their distal ends and transects the at least one first groove; and a second transection channel that transects each channel of the plurality of channels at their proximal ends and transects the at least one second groove. 
     That is, in certain embodiments, there may be provided a plurality of channels, each channel being transected at their distal ends by a first transection channel, and each channel being transected at their proximal ends by a second transection channel. The first transection channel may transect the at least one first groove. The second transection channel may transect the at least one second groove. The plurality of channels may extend across the transverse direction of the substrate. The first transection channel and the second transection channel may extend across the web direction of the substrate. The first transection channel, the second transection channel, or both the first transection channel and the second transection channel may extend perpendicularly to each channel of the plurality of channels. 
     This provides the advantage that electrical shorts across the end of each grooves are substantially prevented. 
     In certain embodiments, the first transection channel transects each channel of the plurality of channels at their distal ends and transects a portion of the first series of grooves, and/or the second transection channel transects each channel of the plurality of channels at their proximal ends and transects a portion of the second series of grooves. 
     In certain embodiments, the first transection channel transects the entirety of the first series of grooves, and/or the second transection channel transects the entirety of the second series of grooves. 
     In certain embodiments, the first transection channel and/or the second transection channel transect the respective groove or grooves towards an end of each groove. 
     In certain embodiments, the plurality of channels comprise a first channel and a second channel, wherein the first transection channel transects the first channel and the second channel at their distal ends, and wherein the second transection channel transects the first channel and the second channel at their proximal ends. 
     That is, in certain embodiments, the plurality of channels comprises a first channel and a second channel. The first channel and the second channel may extend in parallel to one another. The first transection channel transects the first channel and the second channel at their distal ends. The second transection channel transects the first channel and the second channel at their proximal ends. The distal end and the proximal end may be at, or towards, opposing edges, along the transverse direction, of the substrate. 
     In certain embodiments, the plurality of channels further comprises a third channel, wherein the first transection channel further transects the third channel at its distal end, and wherein the second transection channel further transects the third channel at its proximal end. 
     That is, in certain embodiments, the plurality of channels comprises a first channel, a second channel and a third channel. The first channel, the second channel and the third channel may extend in parallel to one another. The first transection channel transects the first channel, the second channel and the third channel at their distal ends. The second transection channel transects the first channel, the second channel and the third channel at their proximal ends. The distal end and the proximal end may be at, or towards, opposing edges, along the transverse direction, of the substrate. 
     In certain embodiments, each channel, the first transection channel and the second transection channel form a substantial Z-shape having a predetermined angle. The substantially Z-shaped feature formed may include any of the features described above in relation to Z-shaped channels, including predetermined angles. 
     In accordance with another aspect of to the invention, there is provided a method of forming a two-terminal device, comprising:
         providing a substrate;   forming a first cell within the substrate, the first cell having a first characteristic resistance;   forming a second cell within the substrate, spaced apart from the first cell along the web direction of the substrate, the second cell having a second characteristic resistance;   forming a first terminal and a second terminal, each terminal being formed towards or at opposing edges of the substrate across the web direction, one or each terminal being formed in electrical connection with the first cell and the second cell;   forming a connecting portion, between the first cell and the second cell, the connecting portion having a third characteristic resistance;   wherein the third characteristic resistance is greater than or equal to at least one of the first characteristic resistance and the second characteristic resistance, such that an electrical charge from the first or second cell is extracted at the first terminal or the second terminal in preference to transferring from the first cell to the second cell across the connecting portion.       

     This provides the advantage that electrical shorts between the first cell and the second cell are prevented. In particular, manufacturing defects, such as the creation of electrical shorts between the first cell and the second cell, may be minimised. Thus, a more efficient and/or reliable two-terminal device may be formed. 
     In certain embodiments, the step of forming a first cell comprises forming at least one first groove within the substrate. 
     In certain embodiments, the step of forming at least one first groove comprises forming a first series of grooves within the substrate. 
     The first series of grooves, which are connected in series, provides voltage addition as a function of the number of grooves within the series. Thus, this provides the advantage that the voltage of the first cell, that is the first series of grooves, can be modified, or tuned, by varying the number of grooves within the first series of grooves. 
     In certain embodiments, the step of forming a second cell comprises forming at least one second groove within the substrate. 
     In certain embodiments, the step of forming at least one second groove comprises forming a second series of grooves within the substrate 
     The second series of grooves, which are connected in series, provides voltage addition as a function of the number of grooves within the series. Thus, this provides the advantage that the voltage of the second cell, that is the second series of grooves, can be modified, or tuned, by varying the number of grooves within the second series of grooves. 
     In certain embodiments, the step of forming a connecting portion further comprises the step of forming at least one resistive element within the connecting portion between the first cell and the second cell, the at least one resistive element providing the third characteristic resistance. 
     In certain embodiments, the at least one resistive element comprises at least one channel. 
     In certain embodiments, the method further comprises:
         coating a first face of each groove of the first series of grooves, each groove of the second series of grooves and the or each channel with a first material;   coating a second face of each groove of the first series of grooves, each groove of the second series of grooves and the or each channel with a second material; and   at least partially filling each groove of the first series of grooves, each groove of the second series of grooves and the or each channel with a third material.       

     In certain embodiments, wherein the step of forming a first cell comprises forming a first series of grooves within the substrate, the step of forming a second cell comprises forming a second series of grooves within the substrate, and the step of forming a connecting portion comprises forming at least one channel within the connecting portion, the method further comprises:
         coating a first face of each groove of the first series of grooves, each groove of the second series of grooves and the or each channel with a first material;   coating a second face of each groove of the first series of grooves, each groove of the second series of grooves and the or each channel with a second material; and   at least partially filling each groove of the first series of grooves, each groove of the second series of grooves and the or each channel with a third material.       

     In certain embodiments, the step of coating the first face with the first material and/or coating the second face with the second material comprises an off-axis directional coating process. 
     In certain embodiments, the step of at least partially filling the grooves and the, or each, channel with the third material comprises printing the third material over the substrate. In this way, as the third material is printed over the substrate, the third material is partially or fully printed into the, or each, groove. 
     In certain embodiments, the step of at least partially filling each groove of the first series of grooves and the second series of grooves comprises filling each groove with the third material thereby providing an electrical connection across each groove of the first series of grooves, and an electrical connection across each groove of the second series of grooves. 
     In certain embodiments, the step of at least partially filling the or each channel comprises filling the or each channel with the third material thereby providing an electrical connection across the or each channel. 
     In accordance with yet another aspect of the invention, there is also provided a two-terminal device, including a substrate comprising: 
     a first cell having a first characteristic resistance, and a second cell, spaced apart from the first cell along the web direction of the substrate, having a second characteristic resistance; 
     a first terminal and a second terminal, each terminal being formed towards or at opposing edges along the transverse direction of the substrate; 
     a connecting portion, between the first cell and the second cell, comprising a channel, the connecting portion having a third characteristic resistance; 
     wherein the channel has an aspect ratio of at least 1:1.6 such that third characteristic resistance is greater than or equal to at least one of the first characteristic resistance and the second characteristic resistance, such that electrical charge is extracted from the first cell and the second cell at the first terminal and the second terminal in preference to electrical charge transfer from the first cell to the second cell across the connecting portion. 
     That is, the third characteristic resistance may be tuned as a function of the depth of the channel. That is, a deeper channel may provide a larger electron transfer path, and thus a higher third characteristic resistance. As discussed above, this prevents electrical shorts. 
     In accordance with yet another aspect of the invention, there is also provided a two-terminal device, including a substrate comprising: 
     at least one first groove having a terminal groove or a terminal portion, the at least one groove having a first characteristic resistance, and at least one second groove having a terminal groove or a terminal end, spaced apart from the at least one first groove along the web direction of the substrate, having a second characteristic resistance; 
     a first terminal and a second terminal, each terminal being formed towards or at opposing edges along the transverse direction of the substrate; 
     a connecting portion, between the terminal groove or terminal portion of the at least one first groove and the terminal groove or terminal portion of the at least one second groove, comprising a channel, the connecting portion having a third characteristic resistance; 
     wherein the channel has an aspect ratio that greater than, preferably between 20% and 50% greater than, an aspect ratio of at least one of the terminal groove or terminal portion of the at least one first groove and the terminal groove or terminal portion of the at least one second groove, such that the third characteristic resistance is greater than or equal to at least one of the first characteristic resistance and the second characteristic resistance, such that electrical charge is extracted from the at least one first groove and the at least one second groove at the first terminal and the second terminal in preference to electrical charge transfer from the terminal groove or terminal portion of the at least one first groove to the terminal groove or terminal portion of the at least one second groove across the connecting portion. 
     That is, the third characteristic resistance may be tuned as a function of the depth of the channel with respect to the adjacent grooves. That is, a channel having a larger, for example 20% to 50% larger, aspect ratio than the adjacent grooves may provide a larger electron transfer path, and thus a higher third characteristic resistance. As discussed above, this prevents electrical shorts. 
     In accordance with yet another aspect of the invention, there is also provided a two-terminal device, including a substrate comprising: 
     a first cell having a first characteristic resistance, and a second cell, spaced apart from the first cell along the web direction of the substrate, having a second characteristic resistance; 
     a first terminal and a second terminal, each terminal being formed towards or at opposing edges along the transverse direction of the substrate; 
     a connecting portion, between the first cell and the second cell, comprising a channel, the connecting portion having a third characteristic resistance; 
     wherein the channel includes a rutted-base, a rutted-wall and/or a non-conductive electrical insulator therein, such that the third characteristic resistance is greater than or equal to at least one of the first characteristic resistance and the second characteristic resistance, such that electrical charge is extracted from the first cell and the second cell at the first terminal and the second terminal in preference to electrical charge transfer from the first cell to the second cell across the connecting portion. 
     That is, the channel may include a rutted-based, a rutted-wall, a non-conducive electrical insulator therein or any combination thereof. This may provide tuneability of the third characteristic resistance. 
     In accordance with yet another aspect of the invention, there is also provided a two-terminal device, including a substrate comprising: 
     a first cell having a first characteristic resistance, and a second cell, spaced apart from the first cell along the web direction of the substrate, having a second characteristic resistance; 
     a first terminal and a second terminal, each terminal being formed towards or at opposing edges along the transverse direction of the substrate; 
     a connecting portion, between the first cell and the second cell, comprising a plurality of channels, wherein the plurality of channels each have a channel resistance, a combination of the channel resistances forming a third characteristic resistance; 
     wherein the third characteristic resistance that is greater than or equal to at least one of the first characteristic resistance and the second characteristic resistance, such that an electrical charge in the first or second cell is extracted at the first terminal or the second terminal in preference to transferring from the first cell to the second cell across the connecting portion. 
     That is, there may be a plurality of channels formed within the connecting portion. This may provide redundancy in the event that one of the plurality of channels fails in its electrical isolation of the first cell and the second cell. Thus, electrical shorts may be prevented between the first cell and the second cell during manufacture of the two-terminal device. 
     In accordance with yet another aspect of the invention, there is also provided a two-terminal device, including a substrate comprising: 
     a first cell having a first characteristic resistance, and a second cell, spaced apart from the first cell along the web direction of the substrate, having a second characteristic resistance; 
     a first terminal and a second terminal, each terminal being formed towards or at opposing edges along the transverse direction of the substrate; 
     a connecting portion, between the first cell and the second cell, comprising a plurality of channels, wherein the plurality of channels each have a channel resistance, a combination of the channel resistances forming a third characteristic resistance; 
     wherein the third characteristic resistance is equal to one of the first characteristic resistance or the second characteristic resistance, and greater than the other of the first characteristic resistance and the second characteristic resistance, such that electrical charge is extracted from the first cell and the second cell at the first terminal and the second terminal in preference to electrical charge transfer from the first cell to the second cell across the connecting portion. 
     As will be clear to a person skilled in the art, any combination of features discussed above or below may be used, provided that such features are not mutually incompatible. By way of an example illustrating this point, the skilled person would recognise that the first cell could comprise at least one groove, and the second cell could comprise a series of grooves. By way of a further example illustrating this point, the skilled person would recognise that any number of resistive elements and any type of resistive elements could be used within the connecting portion, for example, one or more channels in combination with one or more peaks of the substrate, or the like. 
     Certain terminology is used in the following description for convenience only and is not limiting. The words ‘right’, ‘left’, ‘lower’, ‘upper’, ‘front’, ‘rear’, ‘upward’, ‘down’ and ‘downward’ designate directions in the drawings to which reference is made and are with respect to the described component when assembled and mounted. The words ‘inner’, ‘inwardly’ and ‘outer’, ‘outwardly’ refer to directions toward and away from, respectively, a designated centreline or a geometric centre of an element being described (e.g. central axis), the particular meaning being readily apparent from the context of the description. 
     Further, as used herein, the terms ‘connected’, ‘attached’, ‘coupled’, ‘mounted’ are intended to include direct connections between two members without any other members interposed therebetween, as well as, indirect connections between members in which one or more other members are interposed therebetween. The terminology includes the words specifically mentioned above, derivatives thereof, and words of similar import. 
     Further, unless otherwise specified, the use of ordinal adjectives, such as, “first”, “second”, “third” etc. merely indicate that different instances of like objects are being referred to and are not intended to imply that the objects so described must be in a given sequence, either temporally, spatially, in ranking or in any other manner. 
     Below, there is provided a non-exhaustive list of non-limiting examples. Any one or more of the features of these examples may be combined with any one or more features of another example, embodiment or aspect described herein, provided that they are not mutually incompatible. In particular, any one of examples 1 to 56 can be combined with any one of examples 57 to 96, provided that they are not mutually incompatible. 
     Example 1. A two-terminal device, including a substrate comprising: 
     a first cell having a first characteristic resistance, and a second cell, spaced apart from the first cell along the web direction of the substrate, having a second characteristic resistance; 
     a first terminal and a second terminal, each terminal being formed towards or at opposing edges of the substrate across the transverse direction, and each terminal being in electrical communication with the first cell and the second cell; 
     a connecting portion, between the first cell and the second cell, the connecting portion having a third characteristic resistance; 
     wherein the third characteristic resistance is greater than or equal to at least one of the first characteristic resistance and the second characteristic resistance, such that electrical charge is extractable from the first cell and the second cell at the first terminal and the second terminal in preference to electrical charge transfer between the first cell and the second cell across the connecting portion. 
     Example 2. A two-terminal device according to example 1, wherein the third characteristic resistance is greater than at least one of the first characteristic resistance and the second characteristic resistance. 
     Example 3. A two-terminal device according to example 2, wherein the third characteristic resistance is at least two times, preferably at least five times, most preferably at least ten times, greater than at least one of the first characteristic resistance and the second characteristic resistance. 
     Example 4. A two-terminal device according to any preceding example, wherein the connecting portion comprises at least one resistive element. 
     Example 5. A two-terminal device according to example 4, wherein the at least one resistive element comprises a peak of the substrate, a discontinuous non-insulating coating of the substrate, and/or a rutted portion of the substrate. 
     Example 6. A two-terminal device according to example 4 or 5, wherein the at least one resistive element comprises a channel in the substrate. 
     Example 7. A two-terminal device according to example 6, wherein the channel comprises a rutted-base, a rutted-wall and/or a non-conductive electrical insulator material therein. 
     Example 8. A two-terminal device according to example 6 or 7, wherein the channel has an aspect ratio of at least 1:1.6. 
     Example 9. A two-terminal device according to example 8, wherein the channel has an aspect ratio of at least 1:2. 
     Example 10. A two-terminal device according to any preceding example, wherein the first cell comprises at least one first groove and/or the second cell comprises at least one second groove. 
     Example 11. A two-terminal device according to example 10, wherein the first cell comprises a first series of grooves and/or the second cell comprises a second series of grooves. 
     Example 12. A two-terminal device according to example 10, when dependent upon any one of examples 6 to 9, wherein the channel transects a portion of the at least one first groove and/or a portion of the at least one second groove. 
     Example 13. A two-terminal device according to example 11, when dependent upon example 10 and any one of examples 6 to 9, wherein the channel transects a portion of the first series of grooves and/or a portion of the second series of grooves. 
     Example 14. A two-terminal device according to example 13, wherein the channel transects the entirety of the first series of grooves and/or the entirety of the second series of grooves. 
     Example 15. A two-terminal device according to example 13 or example 14, wherein the channel transects the first series of grooves and/or the second series of grooves towards an end of each groove. 
     Example 16. A two-terminal device according to any one of examples 6 to 15, wherein the channel is substantially Z-shaped having a predetermined angle. 
     Example 17. A two-terminal device according to example 4, wherein the at least one resistive element comprises a plurality of channels in the substrate. 
     Example 18. A two-terminal device according to example 17, wherein one or more of the plurality of channels comprises a rutted-base, a rutted-wall and/or a non-conductive electrical insulator therein. 
     Example 19. A two-terminal device according to example 17 or 18, wherein one or more of the plurality of channels has an aspect ratio of at least 1:1.6. 
     Example 20. A two-terminal device according to example 17 or 18, wherein one or more of the plurality of channels has an aspect ratio of at least 1.6:1. 
     Example 21. A two-terminal device according to any one of examples 17 to 20, wherein the first cell comprises at least one first groove and/or the second cell comprises at least one second groove. 
     Example 22. A two-terminal device according to example 21, wherein the first cell comprises a first series of grooves and/or the second cell comprises a second series of grooves. 
     Example 23. A two-terminal device according to example 21, when dependent upon any one of examples 17 to 20, wherein each channel transects the at least one first groove and/or the at least one second groove. 
     Example 24. A two-terminal device according to example 22, when dependent upon example 21 and any one of examples 17 to 20, wherein each channel transects a portion of the first series of grooves and/or a portion of the second series of grooves. 
     Example 25. A two-terminal device according to example 24, wherein each channel transects the entirety of the first series of grooves and/or the entirety of the second series of grooves. 
     Example 26. A two-terminal device according to example 24 or example 25, wherein each channel transects the first series of grooves and/or the second series of grooves towards an end of each groove. 
     Example 27. A two-terminal device according to any one of examples 17 to 26, wherein the plurality of channels comprises a first channel, having a first channel characteristic resistance, and a second channel, having a second channel characteristic resistance, wherein the first channel characteristic resistance and the second channel characteristic resistance provide substantially all of the third characteristic resistance. 
     Example 28. A two-terminal device according to example 27, wherein the plurality of channels further comprises a third channel, having a third channel characteristic resistance, wherein the first channel characteristic resistance, the second channel characteristic resistance and the third channel characteristic resistance provide substantially all of the third characteristic resistance. 
     Example 29. A two-terminal device according to any one of examples 17 to 28, wherein each channel of the plurality of channels is substantially Z-shaped having a predetermined angle. 
     Example 30. A two-terminal device according to example 21, further comprising: 
     a first transection channel that transects each channel of the plurality of channels at their distal ends and transects the at least one first groove; 
     a second transection channel that transects each channel of the plurality of channels at their proximal ends and transects the at least one second groove. 
     Example 31. A two-terminal device according to example 22, further comprising: 
     a first transection channel that transects each channel of the plurality of channels at their distal ends and transects a portion of the first series of grooves; and 
     a second transection channel that transects each channel of the plurality of channels at their proximal ends and transects a portion of the second series of grooves. 
     Example 32. A two-terminal device according to example 31, wherein the first transection channel transects the entirety of the first series of grooves, and wherein the second transection channel transects the entirety of the second series of grooves. 
     Example 33. A two-terminal device according to example 31 or example 32, wherein the first transection channel and/or the second transection channel transect the grooves towards an end of each groove. 
     Example 34. A two-terminal device according to any one of examples 30 to 33, wherein the plurality of channels comprise a first channel and a second channel, wherein the first transection channel transects the first channel and the second channel at their distal ends, and wherein the second transection channel transects the first channel and the second channel at their proximal ends. 
     Example 35. A two-terminal device according to example 34, wherein the plurality of channels further comprises a third channel, wherein the first transection channel further transects the third channel at its distal end, and wherein the second transection channel further transects the third channel at its proximal end. 
     Example 36. A two-terminal device according to any one of examples 30 to 35, wherein each channel, the first transection channel and the second transection channel form a substantial Z-shape having a predetermined angle. 
     Example 37. A two-terminal device according to any preceding example, wherein the two-terminal device is an optoelectronic device. 
     Example 38. A method of forming a two-terminal device, comprising: providing a substrate;
         forming a first cell within the substrate, the first cell having a first characteristic resistance;   forming a second cell within the substrate, spaced apart from the first cell along the web direction of the substrate, the second cell having a second characteristic resistance;   forming a connecting portion, between the first cell and the second cell, the connecting portion having a third characteristic resistance;   wherein the third characteristic resistance is greater than or equal to at least one of the first characteristic resistance and the second characteristic resistance, such that electrical charge is extracted from the first cell and the second cell at the first terminal and the second terminal in preference to electrical charge transfer from the first cell to the second cell across the connecting portion.       

     Example 39. A method according to example 38, wherein the step of forming a first cell comprises forming at least one first groove within the substrate. 
     Example 40. A method according to example 39, wherein the step of forming at least one first groove comprises forming a first series of grooves within the substrate. 
     Example 41. A method according to any one of examples 38 to 40, wherein the step of forming a second cell comprises forming at least one second groove within the substrate. 
     Example 42. A method according to example 41, wherein the step of forming at least one second groove comprises forming a second series of grooves within the substrate 
     Example 43. A method according to any one of examples 38 to 42, wherein the step of forming a connecting portion further comprises the step of forming at least one resistive element within the connecting portion between the first cell and the second cell, the at least one resistive element providing the third characteristic resistance. 
     Example 44. A method according to example 43, wherein the at least one resistive element comprises at least one channel. 
     Example 45. A method according to example 44, when dependent upon examples 40, 42 and 43, further comprising:
         coating a first face of each groove of the first series of grooves, each groove of the second series of grooves and the or each channel with a first material;   coating a second face of each groove of the first series of grooves, each groove of the second series of grooves and the or each channel with a second material; and   at least partially filling each groove of the first series of grooves, each groove of the second series of grooves and the or each channel with a third material.       

     Example 46. A method according to example 45, wherein the step of coating the first face with the first material and/or coating the second face with the second material comprises an off-axis directional coating process. 
     Example 47. A method according to example 45 or 46, wherein the step of at least partially filling the grooves and the or each channel with the third material comprises printing the third material over the substrate. 
     Example 48. A method according to any one of examples 45 to 47, wherein the step of at least partially filling each groove of the first series of grooves and the second series of grooves comprises filling each groove with the third material thereby providing an electrical connection across each groove of the first series of grooves, and an electrical connection across each groove of the second series of grooves. 
     Example 49. A method according to any one of examples 45 to 48, wherein the step of at least partially filling the or each channel comprises filling the or each channel with the third material thereby providing an electrical connection across the or each channel. 
     Example 50: A two-terminal device obtainable according to any one of examples 38 to 49. 
     Example 51: An optoelectronic device obtainable according to any one of examples 38 to 49. 
     Example 52. A two-terminal device, including a substrate comprising: 
     a first cell having a first characteristic resistance, and a second cell, spaced apart from the first cell along the web direction of the substrate, having a second characteristic resistance; 
     a first terminal and a second terminal, each terminal being formed towards or at opposing edges along the transverse direction of the substrate; 
     a connecting portion, between the first cell and the second cell, comprising a channel, the connecting portion having a third characteristic resistance; 
     wherein the channel has an aspect ratio of at least 1:1.6 such that third characteristic resistance is greater than or equal to at least one of the first characteristic resistance and the second characteristic resistance, such that electrical charge is extracted from the first cell and the second cell at the first terminal and the second terminal in preference to electrical charge transfer from the first cell to the second cell across the connecting portion. 
     Example 53. A two-terminal device, including a substrate comprising: 
     at least one first groove having a terminal groove or a terminal portion, the at least one groove having a first characteristic resistance, and at least one second groove having a terminal groove or a terminal portion, spaced apart from the at least one first groove along the web direction of the substrate, having a second characteristic resistance; 
     a first terminal and a second terminal, each terminal being formed towards or at opposing edges along the transverse direction of the substrate; 
     a connecting portion, between the terminal groove or terminal portion of the at least one first groove and the terminal groove or terminal portion of the at least one second groove, comprising a channel, the connecting portion having a third characteristic resistance; 
     wherein the channel has an aspect ratio that greater than, preferably between 20% and 50% greater than, an aspect ratio of at least one of the terminal groove or terminal portion of the at least one first groove and the terminal groove or terminal portion of the at least one second groove, such that the third characteristic resistance is greater than or equal to at least one of the first characteristic resistance and the second characteristic resistance, such that electrical charge is extracted from the at least one first groove and the at least one second groove at the first terminal and the second terminal in preference to electrical charge transfer from the terminal groove or terminal portion of the at least one first groove to the terminal groove or terminal portion of the at least one second groove across the connecting portion. 
     Example 54. A two-terminal device, including a substrate comprising: 
     a first cell having a first characteristic resistance, and a second cell, spaced apart from the first cell along the web direction of the substrate, having a second characteristic resistance; 
     a first terminal and a second terminal, each terminal being formed towards or at opposing edges along the transverse direction of the substrate; 
     a connecting portion, between the first cell and the second cell, comprising a channel, the connecting portion having a third characteristic resistance; 
     wherein the channel includes a rutted-base, a rutted-wall and/or a non-conductive electrical insulator therein, such that the third characteristic resistance is greater than or equal to at least one of the first characteristic resistance and the second characteristic resistance, such that electrical charge is extracted from the first cell and the second cell at the first terminal and the second terminal in preference to electrical charge transfer from the first cell to the second cell across the connecting portion. 
     Example 55. A two-terminal device, including a substrate comprising: 
     a first cell having a first characteristic resistance, and a second cell, spaced apart from the first cell along the web direction of the substrate, having a second characteristic resistance; 
     a first terminal and a second terminal, each terminal being formed towards or at opposing edges along the transverse direction of the substrate; 
     a connecting portion, between the first cell and the second cell, comprising a plurality of channels, wherein the plurality of channels each have a channel resistance, a combination of the channel resistances forming a third characteristic resistance; 
     wherein the third characteristic resistance that is greater than or equal to at least one of the first characteristic resistance and the second characteristic resistance, such that electrical charge is extracted from the first cell and the second cell at the first terminal and the second terminal in preference to electrical charge transfer from the first cell to the second cell across the connecting portion. 
     Example 56. A two-terminal device, including a substrate comprising: 
     a first cell having a first characteristic resistance, and a second cell, spaced apart from the first cell along the web direction of the substrate, having a second characteristic resistance; 
     a first terminal and a second terminal, each terminal being formed towards or at opposing edges along the transverse direction of the substrate; 
     a connecting portion, between the first cell and the second cell, comprising a plurality of channels, wherein the plurality of channels each have a channel resistance, a combination of the channel resistances forming a third characteristic resistance; 
     wherein the third characteristic resistance is equal to one of the first characteristic resistance or the second characteristic resistance, and greater than the other of the first characteristic resistance and the second characteristic resistance, such that electrical charge is extracted from the first cell and the second cell at the first terminal and the second terminal in preference to electrical charge transfer from the first cell to the second cell across the connecting portion. 
     Example 57: A substrate for a two-terminal device, comprising: a first series of grooves and a second series of grooves, each groove having a proximal end and a distal end across the transverse direction of the substrate, and a channel transecting a portion of the first series of grooves and a portion of the second series of grooves towards the proximal end of each groove, and wherein the depth of each groove tends towards the depth of the channel in a transection region towards the proximal end of each groove. 
     Example 58: A substrate according to example 57, wherein the depth of each groove tends non-linearly towards the depth of the channel. 
     Example 59: A substrate according to example 58, wherein the depth of each groove tends gradually towards the depth of the channel. 
     Example 60: A substrate according to example 58 or example 59, wherein the transection region is substantially arcuate. 
     Example 61: A substrate according to example 57, wherein each groove tends linearly towards the depth of the channel. 
     Example 62: A substrate according to example 61, wherein the depth of each groove tends linearly towards the depth of the channel at an angle of between 0° and 90°, excluding 0° and 90°, formed with respect to an axis extending along the elongate base of each groove. 
     Example 63: A substrate according to any one of examples 57 to 62, wherein the channel is substantially Z-shaped having a predetermined angle. 
     Example 64: A substrate according to any one of examples 57 to 63, wherein each groove has an aspect ratio of at least 1:1, preferably at least 1:1.2, from the distal end to the proximal end, excluding the transection region. 
     Example 65: A substrate according to any one of examples 57 to 64, wherein the channel has an aspect ratio of at least 1:1.6. 
     Example 66: A substrate according to any one of examples 57 to 65, wherein the transection region has an aspect ratio that tends from at least 1:1, preferably 1:1.2, to at least 1:1.6. 
     Example 67: A substrate according to any one of examples 57 to 66, wherein the channel transects each groove of the first series of grooves and/or the second series of grooves. 
     Example 68: A substrate according to any one of examples 57 to 67, comprising a plurality of channels. 
     Example 69: A substrate according to example 68, wherein each channel of the plurality of channels transects a portion of the first series of grooves and a portion of the second series of grooves towards the proximal end of each groove. 
     Example 70: A substrate according to example 68, wherein each channel of the plurality of channels transects each groove of the first series of grooves and each groove of the second series of grooves towards the proximal end of each groove. 
     Example 71: A substrate according to any one of examples 68 to 70, wherein each channel of the plurality of channels is substantially Z-shaped having a predetermined angle. 
     Example 72: A substrate according to example 68, further comprising: 
     a first transection channel transecting each channel of the plurality of channels at their distal ends, the first transection channel transecting the entirety the first series set of grooves towards the proximal end of each groove; and 
     a second transection channel transecting each channel of the plurality of channels at their proximal ends, the second transection channel transecting the entirety of the second series of grooves towards the proximal end of each groove. 
     Example 73: A substrate according to example 72, wherein the first transection channel, the plurality of channels, and the second transection channel substantially form a Z-shape having a predetermined angle. 
     Example 74: A substrate according to example 63, example 71 or example 73, wherein the predetermined angle is between approximately 0 degrees and approximately 90 degrees, preferably between approximately 30 degrees and approximately 60 degrees. 
     Example 75: A substrate according to example 74, wherein the predetermined angle is between approximately 40 degrees and approximately 50 degrees, preferably approximately 45 degrees. 
     Example 76: A two-terminal device comprising the substrate of any one of examples 57 to 75. 
     Example 77: A two-terminal device according to example 76, wherein the two-terminal device is an optoelectronic device. 
     Example 78: A method of forming a substrate for a two-terminal device, comprising:
         providing a web of flexible material; and   forming a first series of grooves within the web of flexible material;   forming a second series of grooves within the web of flexible material;   forming a channel between the first series of grooves and the second series of grooves within the web of flexible material, the channel transecting a portion of the first and second series of grooves towards a proximal end of each groove, wherein the step of forming a channel includes forming a depth of each groove that tends towards the depth of the channel at the proximal end of each groove.       

     Example 79: A method according to example 78, wherein the first series of grooves, the second series of grooves and the channel are formed as a unitary step. 
     Example 80: A method according to example 78 or example 79, wherein the step of forming a first series of grooves within the web of flexible material comprises embossing the web of flexible material to form the first series of grooves. 
     Example 81: A method according to any one of examples 78 to 80, wherein the step of forming a second series of grooves within the web of flexible material comprises embossing the web of flexible material to form the second series of grooves. 
     Example 82: A method according to any one of examples 78 to 81, wherein the step of forming a channel within the web of flexible material comprises embossing the web of material to form the channel. 
     Example 83: A method according to any one of examples 80 to 82, wherein the step of embossing comprises:
         providing one or more shims having at least one protrusion corresponding to at least one of the first series of grooves, the second series of grooves and the channel;   coating a surface of the web of flexible material with a UV-curable coating;   engaging the at least one protrusion of the or each shim with the coated web of flexible material;   at least partially UV curing the UV-curable coating; and   removing the at least one protrusion of the or each shim from the coated web of flexible material before the UV-curable coating has fully cured.       

     Example 84: A method according to example 83, wherein the shim is a master shim comprising at least one protrusion corresponding to the first series of grooves, at least one protrusion corresponding to the second series of grooves, and at least one protrusion corresponding to the channel. 
     Example 85: A method according to example 84, wherein the master shim is a Nickel-plated master shim. 
     Example 86: A method according to any one of examples 83 to 85, wherein the or each shim is formed as a cylindrical stamping roll. 
     Example 87: A method according to any one of examples 83 to 85, wherein the or each shim is formed as a stamping plate. 
     Example 88: A method of forming a two-terminal device, comprising:
         forming a substrate according to a method of any one of examples 78 to 87;   coating a first face of first series of grooves, the second series of grooves and the channel with at least one first material;   coating a second opposing face of the first series of grooves, the second series of grooves and the channel with at least one second material; and   at least partially filling the channel with a third material.       

     Example 89: A method according to example 88, wherein the step of coating the first face with the at least one first material and coating the second face with the at least one second material is before the step of at least partially filling the channel with the third material. 
     Example 90: A method according to example 88 or example 89, wherein the step of coating the first face with at least one first material and/or coating the second face with at least one second material comprises an off-axis directional coating process. 
     Example 91: A method according to any one of examples 88 to 90, wherein the step of at least partially filling the channel with a third material comprises printing the third material over the substrate. 
     Example 92: A method according to any one of examples 88 to 91, wherein the at least one first material comprises a non-insulating material. 
     Example 93: A method according to any one of examples 88 to 92, wherein the at least one second material comprises a non-insulating material. 
     Example 94: A method according to any one of examples 88 to 93, wherein the third material comprises a capacitor material, a supercapacitor material, or a perovskite. 
     Example 95: A substrate obtainable by the method of any one of examples 78 to 87. 
     Example 96: A two-terminal device obtainable by the method of any one of examples 88 to 94. 
     Other examples will be apparent from the aforementioned summary of invention and the detailed description noted below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention are further described hereinafter with reference to the accompanying drawings, in which: 
         FIG.  1    illustrates an electrical diagram of a two-terminal device in accordance with the prior art; 
         FIG.  2    illustrates (a) an electrical diagram of a two-terminal device in accordance with the invention and (b) an enlarged view of a portion of the electrical diagram of (a); 
         FIG.  3    illustrates a plan view of a substrate in accordance with one embodiment of the invention; 
         FIG.  4    illustrates a plan view of a substrate in accordance with one embodiment of the invention; 
         FIG.  5    illustrates a plan view of a substrate in accordance with one embodiment of the invention; 
         FIG.  6    illustrates a plan view of a substrate in accordance with one embodiment of the invention; 
         FIG.  7    illustrates (a) a plan view of a substrate in accordance with one embodiment of the invention and (b) a plan view of another substrate in accordance with one embodiment of the invention; 
         FIG.  8    illustrates (a) an enlarged top view of the substrate of  FIG.  5   , (b) an enlarged perspective view of the substrate of  FIG.  5   , (c) another enlarged top view of the substrate of  FIG.  5   , and (d) an enlarged perspective view of the transection region of the substrate of  FIG.  5   ; 
         FIG.  9    illustrates (a) an enlarged perspective view of the substrate of  FIGS.  7 ( a ) , and ( b ) an enlarged perspective view of the transection region of the substrate of  FIG.  7 ( a ) ; 
         FIG.  10    illustrates a cross-sectional view of a groove, a transection region and a channel of a substrate in accordance with one embodiment of the invention; 
         FIG.  11    illustrates a cross-sectional view of a groove, a transection region and a channel of a substrate in accordance with one embodiment of the invention; 
         FIG.  12    illustrates a method of forming a substrate in accordance with one embodiment of the invention; 
         FIG.  13    illustrates a method of forming a substrate in accordance with one embodiment of the invention; 
         FIG.  14    illustrates a method of forming a two-terminal device in accordance with one embodiment of the invention; 
         FIG.  15    illustrates a coating process of the method of  FIG.  14   ; 
         FIG.  16    illustrates a two-terminal device in accordance with one embodiment of the invention; 
         FIG.  17    illustrates a cross-section view of a two-terminal device according to one embodiment of the present invention; 
         FIG.  18    illustrates a cross-section view of a two-terminal device according to another embodiment of the present invention; 
         FIG.  19    illustrates a cross-section view of a two-terminal device according to a further embodiment of the present invention; 
         FIG.  20    illustrates a cross-section view of a two-terminal device according to another embodiment of the present invention; 
         FIG.  21    illustrates a cross-section view of a two-terminal device according to a still further embodiment of the present invention; 
         FIG.  22    illustrates a cross-section view of a two-terminal device according to another embodiment of the present invention; 
         FIG.  23    illustrates a graph comparing the performances of the two-terminal device of  FIG.  1    with the two-terminal device of  FIGS.  2 ( a )  and  3 ; 
         FIG.  24    illustrates a graph depicting the performance of a two-terminal device as described herein; and 
         FIG.  25    illustrates yet another graph depicting the performance of a two-terminal device as described herein. 
     
    
    
     DETAILED DESCRIPTION 
     Like reference numerals are used to depict like features throughout. 
     Various modifications to the detailed designs are described above are envisaged. For example, any number of grooves within any number of series of grooves may be used. Equally, any number of delineation features, such as channels, transection channels or the like may be used. Moreover, any combination of such delineation features may be used. 
     It will be clear to a person skilled in the art that features described in relation to any of the embodiments described above can be application interchangeably between the different embodiments. The embodiments described above are examples to illustrate various features of the invention. 
     Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of them mean “including but not limited to”, and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps. Through the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise. 
     Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect embodiment, or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract or drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed. 
     The reader&#39;s attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference. 
       FIGS.  2 ( a ) and  2 ( b )  illustrate an example of a two-terminal device  50  having a substrate, in accordance with the present invention. The substrate includes a first cell  54   a , a second cell  54   b  and a third cell  54   c . The first, second and third cells  54   a ,  54   b ,  54   c  may be photovoltaic cells as shown in  FIGS.  2 ( a ) and  2 ( b ) . In this specific example, the first, second and third cells  54   a ,  54   b ,  54   c  are formed as a first series of grooves  54   a , a second series of grooves  54   b  and a third series of grooves  54   c . Each series of grooves  54   a ,  54   b ,  54   c  includes a plurality of grooves. 
     As shown in  FIGS.  2 ( a ) and  2 ( b ) , grooves are connected in series with one another to form a first series of grooves  54   a . Likewise, grooves are connected in series to form a second series of grooves  54   b , and further grooves are connected in series to form a third series of grooves  54   c . In this way, the grooves of a respective series of grooves  54   a ,  54   b ,  54   c  is first connected in series to form each of the respective series of grooves  54   a ,  54   b ,  54   c , and then each series of grooves  54   a ,  54   b ,  54   c  is connected in parallel to one another. Thus, the two-terminal device  50  of  FIGS.  2 ( a ) and  2 ( b )  differs from that of the prior art as illustrated in  FIG.  1   . 
     The two-terminal device  50  of  FIGS.  2 ( a ) and  2 ( b )  provides the advantage that bypass diodes, which are typically required in conventional substrates such as those illustrated in  FIG.  1   , are not necessary. Instead, grooves are placed in series relatively close to one another, in some examples with a spacing of approximately 0.1 mm or less between each groove, such that each groove within a series of grooves  54   a ,  54   b ,  54   c  experiences substantially, or exactly, the same lighting conditions, in use. Moreover, since each series of grooves  54   a ,  54   b ,  54   c  is connected in parallel, shading of grooves of an individual series of grooves  54   a ,  54   b ,  54   c  has a less significant impact on the overall performance of the device. Thus, the prerequisite of bypass diodes is negated in the present invention. 
     Furthermore, as shown in  FIGS.  2 ( a ) and  2 ( b ) , the two-terminal device  50  includes a first connecting portion including a first delineation feature  56   a , and a second connecting portion including a second delineation feature  56   b . The first delineation feature  56   a  is provided between the first series of grooves  54   a  and the second series of grooves  54   b . the second delineation feature  54   b  is provided between the second series of grooves  54   b  and the third series of grooves  54   c . Any number of grooves may be present in any number of series of grooves  54   a ,  54   b ,  54   c  having any number of delineation features  56   a ,  56   b  therebetween, as described herein. Further, the delineation feature  56   a ,  56   b  may take any appropriate form as discussed further herein. 
     Each series of grooves  54   a ,  54   b ,  54   c  provides an electrical connection between a first electrical connection  58  and a second electrical connection  60 . The first electrical connection  58  is a positive electrical connection and the second electrical connection  60  is a negative electrical connection in the depicted embodiment. Alternatively, the first electrical connection  58  may be a negative electrical connection and the second electrical connection  60  may be a positive electrical connection. The positive and negative electrical connections  58 ,  60  may be connected to respective terminals, for example, positive and negative busbars  62 ,  64  of the two-terminal device  50 . In this way, positive electrical charge is carried to the positive busbar  62  and negative electrical charge is carried to the opposing negative busbar  64 . The busbars  62 ,  64  may be connected to another electrical element, such as a capacitor or the like. 
     As described herein, the delineation features typically serve to provide an electrical disconnection, or provide electrical isolation, between adjacent series of grooves. However, as described herein, this is oftentimes not possible, and so an electrical short occurs across one or more of the delineation features during manufacture of such devices. In this case, the inventors have surprisingly found that conductive delineations features  56   a ,  56   b , that is delineation features that provide an electrical connection thereacross, can be modelled upon a resistor in parallel with a reverse-biased diode, as shown in  FIG.  2 ( a ) . In this way, each delineation feature  56   a ,  56   b  provides a resistance such that the electrical pathway from a terminal groove of a series of grooves  54   a ,  54   b ,  54   c  to its adjacent electrical connection  58 ,  60  is favoured over the electrical pathway across the delineation feature  56   a ,  56   b . Thus, electrical charge is extractable at positive and negative busbars  62 ,  64  in preference to electrical charge transfer across the delineation feature  56   a ,  56   b , that is, a short circuit across the delineation feature  56   a ,  56   b.    
     Furthermore, the inventors have surprisingly found that if the delineation feature  56   a ,  56   b  is conductive, said delineation feature  56   a ,  56   b  provides charge blocking and substantive electrical isolation between adjacent series of grooves simultaneously. That is, the delineation feature  56   a ,  56   b  provides charge blocking in the same orientation that would be used for a bypass diode. In this way, a conductive delineation feature  56   a ,  56   b  protects the adjacent series of grooves  54   a ,  54   b ,  54   c  from reverse bias damage, that is, from electrical charge flowing in a direction that is opposite to the flow of electrical charge across each groove within the series of grooves  54   a ,  54   b ,  54   c . For example, referring to  FIG.  2 ( b ) , the delineation feature  56   a  prevents electrical charge flowing from positive electrical connection  58 , connected to positive busbar  62 , through the delineation feature  56   a  and towards the grooves and the negative electrical connection  60 , connected to the negative busbar  64 . Thus, it has been found, much to the surprise of the inventors, that not only does a conductive delineation feature  56   a ,  56   b  allow for charge extraction as in non-conductive delineation features, but also that a conductive delineation feature  56   a ,  56   b  can provide protection against reverse bias damage. 
       FIG.  3    illustrates a plan view of a two-terminal device  100  comprising a substrate  102 . The substrate  102  has a surface comprising a plurality of series of grooves  104   a - 104   d . In particular, the substrate  102  comprises a first series of grooves  104   a , a second series of grooves  104   b , a third series of grooves  104   c  and a fourth series of grooves  104   d . Further series of grooves may be provided in the machine direction MD of the substrate  102 . Each groove of the series of grooves  104   a - 104   d  generally run in parallel to one another across the transverse direction TD of the substrate  102 , extending from a proximal end, for example, proximal to a first terminal  112  as described below, to a distal end, for example, distal to the first terminal  112  as described below. A channel  106  is provided between each series of grooves  104   a - 104   d.    
     The two-terminal device  100  may be an optoelectronic device, such as a solar photovoltaic cell. Such a two-terminal device  100  includes a mixture of interdigitated (parallel connected) and cascaded (series connected) grooves  104   a - 104   d . The operating voltage of such a two-terminal device  100  can be controlled by changing the number of series of grooves  104   a - 104   d . Increasing the number of series of grooves  104   a - 104   d  increases the operating voltage of the two-terminal device  100 . Such a two-terminal device  100  can be operated in parallel or a combination of series and parallel arrangement. It may be an advantage of the two-terminal device  100  that this removes the need for extra process steps to be used to connect the cascaded groove structures in series to achieve the desired output voltage. 
     The channel  106  physically separates the cascaded (series connected) grooves  104   a - 104   d . The channel  106  enables the cascaded grooves  104   a - 104   d  to be connected in parallel via electrical connection to first and second terminals  112 ,  114 . In this way, it is possible to extract the desired electric charge generated at the voltage designed by the number of cascaded groove structures  104   a - 104   d.    
     The channel  106 , also referred to as the delineation or structural delineation feature, first crosses the first series of grooves  104   a  towards one end of the substrate  102  and then crosses a spacer  108  between the first series of grooves  104   a  and the second series of grooves  104   b , and subsequently crosses the second series of grooves  104   b  towards the opposite edge of the substrate  102 . Since many of these channels  106  are used, each series of grooves,  104   a ,  104   b  for example, are crossed toward each edge by elements of two successive individual channels  106 , as shown in  FIG.  3   . The channel  106  crosses towards an end of each groove of the series of grooves  104   a ,  104   b ,  104   c ,  104   d . However, in other embodiments, the channel  106  may terminate an end, i.e. cross at an end, of each groove of the series of grooves  104   a ,  104   b ,  104   c ,  104   d.    
     Together, the spacers  108  and channels  106  divide the substrate  102  into a first area  110   a  and a second area  110   b . The first area  110   a  carries a positive charge and the second area  110   b  carries a negative charge. The first area  110   a  terminates at a first or positive terminal  112  at one edge of the substrate  102 , and the second area  110   b  terminates at a second or negative terminal  114  at the other, opposite, edge of the substrate  102 , referring to the transverse direction TD. The first area  110   a  provides an electrical connection of the first groove of each series of grooves  104   a - 104   d  to the first terminal  112 . The second area  110   b  provides an electrical connection of the last groove of each series of grooves  104   a - 104   d  to the second terminal  114 . Thus, a two-terminal device  100  having a first terminal  112  and a second terminal  114  is formed. 
       FIG.  4    illustrates a plan view of another two-terminal device  200  comprising a substrate  202 . The substrate  202  has a surface comprising a plurality of series of grooves  204   a - 204   d . In particular, the substrate  202  comprises a first series of grooves  204   a , a second series of grooves  204   b , a third series of grooves  204   c  and a fourth series of grooves  204   d . Further series of grooves may be provided in the machine direction MD of the substrate  202 . Each groove of the series of grooves  204   a - 204   d  generally run in parallel to one another across the transverse direction TD of the substrate  202 , extending from a proximal end, for example, proximal to a first terminal  212  as described below, to a distal end, for example, distal to the first terminal  212  as described below. A channel  206 , in this case a plurality of channels  206   a - 206   c , is provided between each series of grooves  204   a - 204   d.    
     The two-terminal device  200  may be an optoelectronic device, such as a solar photovoltaic cell. Such a two-terminal device  200  includes a mixture of interdigitated (parallel connected) and cascaded (series connected) grooves  204   a - 204   d . The operating voltage of such a two-terminal device  200  can be controlled by changing the number of series of grooves  204   a - 204   d . Increasing the number of series of grooves  204   a - 204   d  increases the operating voltage of the two-terminal device  200 . Such a two-terminal device  200  can be operated in parallel or a combination of series and parallel arrangement. It may be an advantage of the two-terminal device  200  that this removes the need for extra process steps to be used to connect the cascaded groove structures in series to achieve the desired output voltage. 
     Each channel of the plurality of channels  206   a - 206   c  physically separates the cascaded (series connected) grooves  204   a - 204   d . Each of the plurality of channels  206   a - 206   c  enables the cascaded (series connected) grooves  204   a - 204   d  to be electrically connected in parallel to first and second terminals  212 ,  214 . In this way, it is possible to extract the desired electric charge generated at the voltage designed by the number of cascaded groove structures  204   a - 204   d.    
     The first channel  206   a , also referred to as the first delineation or structural delineation feature, first crosses the first series of grooves  204   a  towards one end of the substrate  202  and then crosses a space  208  between the first series of grooves  204   a  and the second series of grooves  204   b , and subsequently crosses the second series of grooves  204   b  towards the opposite edge of the substrate  202 . Since many of these channels are used, each series of grooves,  204   a ,  204   b  for example, are crossed toward each edge by elements of two successive individual channels, as shown in  FIG.  4   . The first channel  206   a  crosses towards an end of each groove of the series of grooves  204   a ,  204   b ,  204   c ,  204   d . However, in other embodiments, the first channel  206   a  may terminate an end, i.e. cross at an end, of each groove of the series of grooves  204   a ,  204   b ,  204   c ,  204   d.    
     The second channel  206   b , like the first channel  206   a , first crosses the first series of grooves  204   a  towards one end of the substrate  202  and then crosses a spacer  208  between the first series of grooves  204   a  and the second series of grooves  204   b , and subsequently crosses the second series of grooves  204   b  towards the opposite edge of the substrate  202 . The third channel  206   c  crosses the first series of grooves  204   a , the spacer  208 , and the second series of grooves  204   b , in the same manner as the first channel  206   a  and the second channel  206   b.    
     It may be advantageous to use a plurality of channels  206   a - 206   c  to mitigate the likelihood of an electrical short forming across the interface between the first series of grooves  204   a  and the second series of grooves  204   b , that is, across the plurality of channels  206   a - 206   c . Thus, a plurality of channels  206   a - 206   c  ensure a more efficient and reliable two-terminal device  200 . 
     Together, the spacers  208  and channels  206  divide the substrate  202  into a first area  210   a  and a second area  210   b . The first area  210   a  carries a positive charge and the second area  210   b  carries a negative charge. The first area  210   a  terminates at a first or positive terminal  212  at one edge of the substrate  202 , and the second area  210   b  terminates at a second or negative terminal  214  at the other, opposite, edge of the substrate  202 , referring to the transverse direction TD. The first area  210   a  provides an electrical connection of the first groove of each series of grooves  204   a - 204   d  to the first terminal  212 . The second area  210   b  provides an electrical connection of the last groove of each series of grooves  204   a - 204   d  to the second terminal  214 . Thus, a two-terminal device  200  having a first terminal  212  and a second terminal  214  is formed. 
       FIG.  5    illustrates a plan view of yet another two-terminal device  300  comprising a substrate  302 . The substrate  302  has a surface comprising a plurality of series of grooves  304   a - 304   d . In particular, the substrate  302  comprises a first series of grooves  304   a , a second series of grooves  304   b , a third series of grooves  304   c  and a fourth series of grooves  304   d . Further series of grooves may be provided in the machine direction MD of the substrate  302 . Each groove of the series of grooves  304   a - 304   d  generally run in parallel to one another across the transverse direction TD of the substrate  302 , extending from a proximal end, for example, proximal to a first terminal  312  as described below, to a distal end, for example, distal to the first terminal  312  as described below. A delineation feature ( 306   a ,  306   b ,  306   c ,  316 ,  318 ) is provided between each series of grooves  304   a - 304   d.    
     The two-terminal device  300  may be an optoelectronic device, such as a solar photovoltaic cell. Such a two-terminal device  300  includes a mixture of interdigitated (parallel connected) and cascaded (series connected) grooves  304   a - 304   d . The operating voltage of such a two-terminal device  300  can be controlled by changing the number of series of grooves  304   a - 304   d . Increasing the number of series of grooves  304   a - 304   d  increases the operating voltage of the two-terminal device  300 . Such a two-terminal device  300  can be operated in parallel or a combination of series and parallel arrangement. It may be an advantage of the two-terminal device  300  that this removes the need for extra process steps to be used to connect the cascaded groove structures in series to achieve the desired output voltage. 
     The delineation features ( 306   a ,  306   b ,  306   c ,  316 ,  318 ) physically separates the cascaded (series connected) grooves  304   a - 304   d . The delineation features enables the cascaded (series connected) grooves  304   a - 304   d  to be connected in parallel via electrical connection to first and second terminals  312 ,  314 , In this way, it is possible to extract the desired electric charge generated at the voltage designed by the number of cascaded groove structures  304   a - 304   d.    
     The delineation feature comprises a plurality of channels, specifically a first channel  306   a , a second channel  306   b  and a third channel  306   c . Each channel  306   a - 306   c  is connected at their distal ends to a first transection channel  316 , and connected at their proximal ends to a second transection channel  318 . The first and second transection channels  316 ,  318  form part of the delineation feature and may be substantially channel-like, or may be further channels. The first and second transection channels  316 ,  318  generally connect to each channel  306   a - 306   c  perpendicularly at their respective ends. The first transection channel  316  first crosses the first series of grooves  304   a  towards one end of the substrate  302  and then crosses a spacer  308  between the first series of grooves  304   a  and the second series of grooves  304   b , and subsequently crosses the second series of grooves  304   b  towards the opposite edge of the substrate  302 . Since many of these delineation features are used, each series of grooves,  304   a ,  304   b  for example, are crossed toward each edge by elements of two successive transection channels  316 ,  318 , as shown in  FIG.  5   . The delineation feature, specifically transection channels  316 ,  218  crosses towards an end of each groove of the series of grooves  304   a ,  304   b ,  304   c ,  304   d . However, in other embodiments, the transection channels  316 ,  318  may terminate an end, i.e. cross at an end, of each groove of the series of grooves  304   a ,  304   b ,  304   c ,  304   d.    
     It may be advantageous to use a plurality of channels  306   a - 306   c  between the series of grooves to mitigate the likelihood of an electrical short forming across the interface between the first series of grooves  304   a  and the second series of grooves  304   b , that is, across the delineation feature. Furthermore, the described arrangement, specifically of transection channels  316 ,  318  at each end of each channel  306   a - 306   c , may provide for an easier manufacture of such efficient and reliable substrates. 
     Together, the spacers  308  and the plurality of channels  306   a - 306   c  divide the substrate  302  into a first area  310   a  and a second area  310   b . The first area  310   a  carries a positive charge and the second area  310   b  carries a negative charge. The first area  310   a  terminates at a first or positive terminal  312  at one edge of the substrate  302 , and the second area  310   b  terminates at a second or negative terminal  314  at the other, opposite, edge of the substrate  302 , referring to the transverse direction TD. The first area  310   a  provides an electrical connection of the first groove of each series of grooves  304   a - 304   d  to the first terminal  312 . The second area  310   b  provides an electrical connection of the last groove of each series of grooves  304   a - 304   d  to the second terminal  314 . Thus, a two-terminal device  300  having a first terminal  312  and a second terminal  314  is formed. 
       FIG.  6    illustrates a plan view of yet another two-terminal device  400  comprising a substrate  402 . The substrate  402  has a surface comprising a plurality of series of grooves  404   a - 404   c . In particular, the substrate  402  comprises a first series of grooves  404   a , a second series of grooves  404   b , and a third series of grooves  404   c . Further series of grooves may be provided in the machine direction MD of the substrate  402 . Each groove of the series of grooves  404   a - 404   c  generally run in parallel to one another across the transverse direction TD of the substrate  402 , extending from a proximal end, for example, proximal to a first terminal  412  as described below, to a distal end, for example, distal to the first terminal  412  as described below. A channel  406  is provided between each series of grooves  404   a - 404   c.    
     The two-terminal device  400  may be an optoelectronic device, such as a solar photovoltaic cell. Such a two-terminal device  400  includes a mixture of interdigitated (parallel connected) and cascaded (series connected) grooves  404   a - 404   c . The operating voltage of such a two-terminal device  400  can be controlled by changing the number of series of grooves  404   a - 404   c . Increasing the number of series of grooves  404   a - 404   c  increases the operating voltage of the two-terminal device  400 . Such a two-terminal device  400  can be operated in parallel or a combination of series and parallel arrangement. It may be an advantage of the two-terminal device  400  that this removes the need for extra process steps to be used to connect the cascaded groove structures in series to achieve the desired output voltage. 
     The channel  406  physically separates the cascaded (series connected) grooves  404   a - 404   c . The channel  406  enables the cascaded grooves  404   a - 404   c  to be connected in parallel via electrical connection to first and second terminals  412 ,  414 . In this way, it is possible to extract the desired electric charge generated at the voltage designed by the number of cascaded groove structures  404   a - 404   c.    
     The channel  406 , also referred to as a delineation feature or structural delineation feature, comprises first region, extending along the machine direction MD, a second region extending along the machine direction MD and substantially parallel to the first region, and a third region therebetween extending along the transverse direction TD and connecting the first region to the second region. The channel  406  first crosses the first series of grooves  404   a  towards one end of the substrate  402  and then crosses a spacer  408  between the first series of grooves  404   a  and the second series of grooves  404   b , and subsequently crosses the second series of grooves  404   b  towards the opposite edge of the substrate  402 . Since many of these channels  406  are used, each series of grooves,  404   a ,  404   b  for example, are crossed toward each edge by elements of two successive channels  406 , as shown in  FIG.  6   . The channel  406  terminates, i.e. crosses at, an end of each groove of the series of grooves  404   a ,  404   b ,  404   c . However, in other embodiments, the channel  406  may cross towards an end, i.e. it may not terminate an end, of each groove of the series of grooves  404   a ,  404   b ,  404   c.    
     Moreover, the channel  406  are substantially Z-shaped in the depicted embodiment. As shown in  FIG.  6   , a first predetermined angle, a, is formed between the first region of the channel  406  and the third region of the channel  406 . A second predetermined angle, β, is formed between the second region of the channel  406  and the third region of the channel  406 . In this example, α=β, however, in other examples, α≠β. In this specific example, α and β are approximately 70 degrees. α and β may have a different value in other examples, for example, any value between 1 degree and 179 degrees. 
     It may be desirable to use a Z-shaped channel  406  as this can be advantageous during the manufacture of such substrates. As described further below, such substrates are coated using off-axis directional coating methods. Thus, by providing an angle between the various regions of the channel  406 , the shadowing effect is increased, thereby providing regions of the channel  406  that are not coated with material. In this way, the likelihood of a short circuit across the channel  406  is mitigated, as described further below. 
     Together, the spacers  408  and the channels  406  divide the substrate  402  into a first area  410   a  and a second area  410   b . The first area  410   a  carries a positive charge and the second area  410   b  carries a negative charge. The first area  410   a  terminates at a first or positive terminal  412  at one edge of the substrate  402 , and the second area  410   b  terminates at a second or negative terminal  414  at the other, opposite, edge of the substrate  402 , referring to the transverse direction TD. The first area  410   a  provides an electrical connection of the first groove of each series of grooves  404   a - 404   c  to the first terminal  412 . The second area  410   b  provides an electrical connection of the last groove of each series of grooves  404   a - 404   c  to the second terminal  414 . Thus, a two-terminal device  400  having a first terminal  412  and a second terminal  414  is formed. 
       FIGS.  7 ( a ) and  7 ( b )  illustrates a plan view of yet another two-terminal device  500  comprising a substrate  502 . The two-terminal device  500  of  FIGS.  7 ( a ) and  7 ( b )  is similar in construction to the two-terminal device of  FIG.  6   . That is, the two-terminal device  500  includes a substrate  502 , a plurality of series of grooves  504   a - 504   d , a channel  506 , a spacer  508 , a first area  510   a  carrying a positive charge, a second area  510   b  carrying a negative charge, and first and second terminals  512 ,  514 . These features are described in relation to  FIG.  6    and are not discussed further here. 
     The two-terminal device  500  of  FIGS.  7 ( a ) and  7 ( b )  differs from  FIG.  6    in that the first and second predetermined angles α, β are formed differently. In  FIG.  6   , the third region of the channel  406  is angled and the first and second regions are substantially perpendicular to the series of grooves  404   a - 404   c . However, as shown in  FIG.  7 ( a ) , in the present example of the two-terminal device  500 , the third region of the channel  506  extends substantially in parallel to the series of grooves  504   a - 504   d , and the first and second regions are formed at an angle with respect to the third region. In the depicted example, α=β, however, in other examples, α≠β. In this specific example, α and β are approximately 45 degrees. In some examples (not shown), α and β may be greater than 90 degrees, for example, up to, but not including, 180 degrees. As shown in  FIG.  7 ( b ) , the delineation feature may take any shape, having any angle, disposed in any appropriate manner on the substrate. 
     It may be desirable to use a Z-shaped channel  506  as this can be advantageous during the manufacture of such substrates. As described further below, such substrates are coated using off-axis directional coating methods. Thus, by providing an angle between the various regions of the channel  506 , the shadowing effect is increased, thereby providing regions of the channel  506  that are not coated with material. In this way, the likelihood of a short circuit across the channel  506  is mitigated, as described further below. Moreover, the Z-shaped channel  506  may be preferred as it allows for a more efficient use of space between the series of grooves  504   a - 504   d.    
       FIGS.  8 ( a ) to  8 ( d )  illustrate various views of the two terminal device  300  as shown in  FIG.  5   . Like numerals denote like features in  FIGS.  8 ( a ) to  8 ( d ) . As best shown in  FIGS.  8 ( c ) and  8 ( d ) , the two-terminal device  300  includes a series of grooves  304 , each groove having a groove base  350 . The delineation feature, specifically the transection channels  316 ,  318  of the delineation feature, each includes a channel base  354 . As can be seen in  FIGS.  8 ( a ) to  8 ( d ) , and with further reference to  FIGS.  10  and  11    as discussed below, the groove base  350  has a substantially constant depth across the elongate width of the grooves  304 . Additionally, the groove base  350  tends towards the channel base  354  in a transection region  352 . That is, the depth of each groove of the grooves  304  tends towards the depth of the delineation feature, or channel, in this example the transection channels  316 ,  318 , within a transection region  352 . This is described in further detail below, with reference to  FIGS.  10  and  11   . 
       FIGS.  9 ( a ) and  9 ( b )  illustrate various views of the two-terminal device  500  as shown in  FIG.  7 ( a ) . Like numerals denote like features in  FIGS.  9 ( a ) and  9 ( b ) . The two-terminal device  500  includes a series of grooves  504 , each groove having a groove base  550 . The delineation feature, specifically the channel  506 , includes a channel base  554 . As best shown in  FIG.  9 ( b ) , and with further reference to  FIGS.  10  and  11    as discussed below, the groove base  550  has a substantially constant depth across the elongate width of the grooves  504 . Additionally, the groove base  550  tends towards the channel base  554  in a transection region  552 . That is, the depth of each groove of the grooves  504  tends towards the depth of the delineation feature, in this example, the channel  506 , within a transection region  552 . This is described in further detail below, with reference to  FIGS.  10  and  11   . 
       FIG.  10    illustrates a cross-sectional view of one example of a transection region between a groove and a channel that can be applied to any of the examples discussed herein. Specifically,  FIG.  10    shows a substrate  602  having a groove  604  of a series of grooves, and a channel  606 . The channel  606  transects the groove  604  at its proximal end. The groove  604  includes a groove base  650 , and the channel  606  includes a channel base  654 . 
     The groove  604 , specifically the groove base  650 , tends towards the channel  606 , specifically the channel base  654 , in a transection region  652 . The transection region  652  has a transection region base  656  that is substantially arcuate in the example shown. That is, the transection region base  656  has a variable depth as it tends from the groove base  650  to the channel base  654 . The variable depth is non-linear in the depicted example. 
       FIG.  11    illustrates another example of a transection region between a groove and a channel that can be applied to any of the examples discussed herein. Specifically,  FIG.  11    shows a substrate  702  having a groove  704 , of a series of grooves, and a channel  706 . The channel  706  transects the groove  704  at its proximal end. The groove  704  includes a groove base  750 , and the channel  706  includes a channel base  754 . 
     The groove  704 , specifically the groove base  750 , tends towards the channel  706 , specifically the channel base  754 , in a transection region  752 . The transection region  752  has a transection region base  756  that is substantially linear, or straight, in the example shown. That is, the transection region base  756  has a variable depth as it tends from the groove base  750  to the channel base  754 . The variable depth is linear in the depicted example. 
     As shown in  FIG.  11   , the linear transection region  752  forms an angle γ with respect to an imaginary axis, formed as a continuation of the groove base  750 . The angle γ is shown as approximately 45 degrees in the depicted example. However, other angles may be used. 
       FIG.  12    illustrates a method  800  of forming a substrate as described herein. The method  800  includes the step of providing  810  a web of flexible material, forming  820  a first series of grooves within the web of flexible material, forming  830  a second series of grooves within the web of flexible material, and forming  840  a channel between the first series of grooves and the second series of grooves within the web of flexible material. 
     The respective steps  810 ,  820 ,  830 ,  840  may be carried out sequentially, that is in an order. For example, the steps  810 ,  820 ,  830 ,  840  may be carried out in the order as described in  FIG.  12   . Alternatively, the steps  810 ,  820 ,  830 ,  840  may be carried out in any other order. For example, the step of forming  840  the channel may take place between forming  820  the first series of grooves and forming  830  the second series of grooves. Further, two or more, or all, of steps  810 ,  820 ,  830 ,  840  may be carried out simultaneously, or concurrently, that is at the same time. For example, the steps of forming  820  the first series of grooves, forming  830  the second series of grooves, and forming  840  the channel may all take place simultaneously. 
     The step of forming  840  the channel further includes forming the channel such that the channel transects a portion of the first series of grooves and the second series of grooves towards a proximal end of each groove. Furthermore, the step of forming  840  the channel includes forming a depth of each groove that tends towards the depth of the channel at the proximal end of each groove. 
     In some examples, one or more of the steps of forming  820  a first series of grooves, forming  830  a second series of grooves and forming  840  a channel therebetween includes an embossing process, as described in relation to  FIG.  13   . 
       FIG.  13    illustrates a specific method  900  of forming a substrate as described herein. The method  900  may be a specific example of the method  800  of  FIG.  12   , for example, the method  900  may represent an embossing process. The method  900  starts by providing  910  a web of flexible material  902 . The method  900  also includes the step of coating  920  the web of flexible material  902  with a UV-curable composition, thereby forming a UV-curable coating  904  on at least one surface of the web of flexible material  902 . The method may also include the step of engaging  930  the coated web of flexible material ( 902 ,  904 ) with a shim, shown in this particular example as a master shim being a cylindrical stamping roll  906 . In other examples, there may be a plurality of shims, a single master shim, or a stamping plate formed as one or more of the plurality of shims or as the single master shim. That is, the skilled person would recognise that the shim need not be a master shim, nor need it be a cylindrical stamping roll  906 . In the example shown, the cylindrical stamping roll  906  includes a series of protrusions  908 . The protrusions  908  correspond to the first series of grooves, the second series of grooves and the channel, as described further below. 
     As the protrusions  908  engage the coated web of flexible material ( 902 ,  904 ), the UV-curable coating  904  is at least partially UV-cured  940  during the engagement step  930 . The protrusions  908  are then removed  950  from the coated web of flexible material ( 902 ,  904 ). As the protrusions  908  are removed  950 , the coated web of flexible material ( 902 ,  904 ) is caused to be drawn towards the protrusions  908  of the cylindrical stamping roll  906  as they are removed  950 , due to the partial UV-curing of the UV-curable coating  904 . However, since the UV-curable coating  904  is only partially UV-cured, that is not fully cured, the coated web of flexible material ( 902 ,  904 ) then relaxes as the protrusions  908  of the cylindrical stamping roll  906  are fully removed. In this way, the transection region between the first series of grooves or the second series of grooves and the channel is first caused to be drawn upwardly, towards the cylindrical stamping roll  906 , and then relaxes, such that the transection region is formed in a manner such that the depth of the grooves tends towards the depth of the channel, as described above. 
     The cylindrical stamping roll  906  is continually rolled  960  across the machine direction MD of the coated web of flexible material ( 902 ,  904 ). Thus, the process is repeated along the machine direction MD. It may also be desirable to cut the formed substrate at various intervals along the machine direction MD. In such cases, the method  900  may optionally include the step of cutting the master substrate into a plurality of substrates. 
       FIG.  14    illustrates a method  1000  of forming a two-terminal device having a substrate as described herein. The method  1000  may be a continuation of method  800  of  FIG.  12    or method  900  of  FIG.  13   . The method  1000  starts by providing, or forming,  1010  a substrate  1001  as described herein. The method  1000  may also include coating  1020  a first face  1002  of a first series of grooves  1006 , a second series of grooves  1008  and a channel  1011  with a first material  1012 . The method  1000  may also include coating  1040  a second face  1004  of the first series of grooves  1006 , the second series of grooves  1008  and the channel  1010  with a second material  1014 . The first material  1012  and the second  1014  may be different. 
     The coating steps  1020 ,  1040  may comprise an off-axis directional coating as best shown in  FIGS.  14 , and  15   ( a ) to  15 ( c ). That is, the coating steps  1020 ,  1040  may comprise coating at an angle formed with respect to the plane of the substrate  1001 . As shown in  FIG.  15   , such an angle δ may be in the range of 30 to 70 degrees, for example approximately 45 degrees. 
       FIGS.  15 ( a ) and  15 ( b )  illustrate a coating process, of the substrates  FIGS.  10  and  11   , respectively.  FIG.  15 ( c )  further illustrates a comparison coating process without having the transection regions of  FIGS.  10  and  11    as described.  FIGS.  15 ( a ) and  15 ( b )  illustrate a coating process having an incident coating angle θ. The arrow C illustrates the incoming coating of a material. As shown, the transection region  652 ,  752 , tending from the groove depth  650 ,  750  to the channel depth  654 ,  754 , as described above, ensures that a large proportion of the transection region  652 ,  752 , that is the region connecting the grooves  604 ,  704  to the channel  606 ,  706 , is shadowed, indicated by the region below arrow C, by the wall W of the channel  606 ,  706  during the coating process. In this way, during the coating process, a large proportion of the transection region  652 ,  752  is not coated with an incoming material. Thus, once the grooves  604 ,  704  and the channel  606 ,  706  are filled with a material that allows for an electrical pathway, as described below, the lack of coated material in the transection region  652 ,  752  ensures that there is no electrical connection between the grooves  604 ,  704  and the channel  606 ,  706 . 
     In comparison, referring to  FIG.  15 ( c ) , without the transection regions  652 ,  752  that tend from the groove depth to the channel depth as described, the interface between an adjacent series of grooves  780  and the channel  790  is coated with material at the same incident coating angle δ as in  FIGS.  15 ( a ) and  15 ( b ) . That is, in the example of  FIG.  15 ( c ) , the creation of an electrical short during manufacture is solely dependent upon the amount of material to be filled in the grooves  780  and the channel  790 . This is known to be difficult to control. Whereas, electrical shorts are mitigated through the use of a transection region in which the groove depth tends to the channel depth, thus increasing the shadowing of the region between the grooves and the channel during manufacture. 
     The method  1000  further includes the step of at least partially filling  1060  the channel  1010  with a third material  1016 . The third material  1016  may be different to the first material  1012  and the second material  1014 . In some examples, the step of at least partially filling  1060  the channel  1010  may comprise a printing process. In addition to the channel  1010  being filled with a third material  1016 , the first series of grooves  1006 , the second series of grooves  1008 , or both the first and second series of grooves  1006 ,  1008  may be at least partially filled with the same third material  1016 , as shown in  FIG.  14   .  FIG.  14    illustrates an embodiment in which the channel  1004  is filled, or completely filled, with the third material  1016 . 
     The first material  1012 , the second material  1014  and the third material  1016  vary depending on the intended use of the two-terminal device that is to be formed. For example, in some cases it may be desirable to produce a solar photovoltaic device that can supply electricity to a device. In this example, the first material  1012  may be a non-insulating material, such as a conductor or a semiconductor, the second material  1014  may be a non-insulating material, such as a conductor or a semiconductor, and the third material  1016  may be a perovskite structured material. As would be recognised by the person skilled in the art, the two-terminal device can be produced with the appropriate coatings that are suitable for the intended final use of the two-terminal device to be produced. 
       FIG.  16    illustrates a two-terminal device  1100  including a substrate  1102  as described herein. The substrate  1102  includes a first series of grooves  1104 , a second series of grooves  1106  and a channel  1108  therebetween. The channel  1108  may have a greater depth than that of the grooves  1104 ,  1106 , as shown. 
     The first series of grooves  1104  include a first face  1104   a , a second, opposing, face  1104   b , and a cavity  1104   c  therebetween. The second series of grooves  1106  include a first face  1106   a , a second, opposing, face  1106   b , and a cavity  1106   c  therebetween. The channel  1108  includes a first face  1108   a , a second, opposing, face  1108   b , and a cavity  1108   c  therebetween. The first faces  1104   a ,  1106   a ,  1108   a  are coated with a first material  1110 . The second face  1104   b ,  1106   b ,  1108   b  are coated with a second material  1112 . Additionally, a third material  1114  is provided within the cavities  1104   c ,  1106   c ,  1108   c . As shown in  FIG.  16   , the cavities  1104   c ,  1106   c  of the first and second series of grooves  1104 ,  1106  are filled to the extent that the first material  1110  and the second material  1112  on opposing faces ( 1104   a ,  1104   b  and  1106   a ,  1106   b ) are in contact with the third material  1114 . In this way, an electrical pathway is formed across the first series of grooves  1104  and the second series of grooves  1106 . 
     As can be seen in  FIG.  16   , the cavity  1108   c  of the channel  1108  is filled with the third material  1114  such that the third material  1114  is in contact with the first material  1110  on the first face  1108   a  or the second material  1112  on the second face  1108   b . Thus, an electrical pathway is provided. However, due to the nature of the substrate described herein and the methods of formation thereof, the cavity  1108   c  of the channel  1108  could be filled with the third material  1114  to a lesser extent. Thus, even if the cavity  1108   c  is filled to a large extent as shown, it would not make contact with the first material  1110  or the second material  1112  within the transection region in which the grooves  1104 ,  1106  meet with the channel  1108 . In this way, an electrical pathway, and thus an electrical short, is prevented across the channel  1108 , whilst allowing for a more simple manufacturing process. 
       FIG.  17    illustrates a two-terminal device  1200 . The two-terminal device  1200  includes a substrate  1202 . The substrate  1202  has a first cell and a second cell that is spaced apart from the first cell. The second cell is spaced from the first cell along the substrate  1202  along the web direction of the substrate  1202 . The first cell is provided with a first series of grooves  1204 . Each of the first series of grooves  1204  include a first face  1204   a , a second, opposing, face  1204   b , and a cavity  1204   c  therebetween. The second cell is provided with a second series of grooves  1206 . Each of the second series of grooves  1206  include a first face  1206   a , a second, opposing, face  1206   b , and a cavity  1206   c  therebetween. A connecting portion including a first channel  1208  and a second channel  1209  is provided between the first cell and the second cell. The first channel  1208  has a first face  1208   a , a second, opposing, face  1208   b , and a cavity  1208   c  therebetween. The second channel  1209  is provided between the first channel  1208  and the second cell. The second channel  1209  has a first face  1209   a , a second, opposing, face  1209   b , and a cavity  1209   c  therebetween. In other examples, one channel  1208  is provided between the first cell and the second cell. In other additional examples, more than two channels  1208 ,  1209  are provided between the first cell and the second cell. The substrate  1202  is provided with a first terminal and a second terminal. The first and second terminals are formed at opposing edges of the substrate  1202  across the transverse direction of the substrate  1202 . The first and second terminals are electrically connected to the first cell and the second cell in a manner similar to that described in relation to  FIGS.  3  to  7   . That is, the first and second terminals are in electrical communication with each of the first cell and the second cell. In some examples, one, or both, of the cavities  1208   c ,  1209   c  may be filled to the extent that the third material  1214  within those cavities  1208   c ,  1209   c  contact the first material  1210  and the second material  1212  to provide an electrical connection thereacross. However, due to the combined resistance of the channels  1208 ,  1209 , as discussed further below, charge from the first or second cell is extracted at the first and second terminals of the device rather than being transferred across the connecting portions  1208 ,  1209 . 
     The first faces  1204   a ,  1206   a ,  1208   a ,  1209   a  are coated with a first material  1210 . The second faces  1204   b ,  1206   b ,  1208   b ,  1209   b  are coated with a second material  1212 . Additionally, a third material  1214  is provided within the cavities  1204   c ,  1206   c ,  1208   c ,  1209   c . The cavities  1204   c ,  1206   c  of the first and second series of grooves  1204 ,  1206  are filled to the extent that the first material  1210  and the second material  1212  on opposing faces ( 1204   a ,  1204   b  and  1206   a ,  1206   b ) are in contact with the third material  1214 . This forms an electrical pathway across the first series of grooves  1204  of the first cell, and between the second series of grooves  1206  of the second cell. 
     The cavity  1208   c  of the first channel  1208  is partially filled with the third material  1214  such that the third material  1214  in the cavity  1208   c  does not contact the first material  1210  on the first face  1208   a  and the second material  1212  on the second face  1208   b . No electrical pathway is provided between the third material  1214  and the first material  1210  on the first face  1208   a . No electrical pathway is provided between the third material  1214  and the second material  1212  on the second face  1208   b . The cavity  1209   c  of the second channel  1209  is partially filled with the third material  1214  such that the third material  1214  in the cavity  1209   c  does not contact the first material  1210  on the first face  1209   a  and the second material  1212  on the second face  1209   b . No electrical pathway is provided between the third material  1214  and the first material  1210  on the first face  1209   a . No electrical pathway is provided between the third material  1214  and the second material  1212  on the second face  1209   b . The first and second channels  1208 ,  1209  ensure there is an electrical resistance from one side of the connecting portion to the other. 
     In use, the combined resistance across the first and second channels  1208 ,  1209 , that is the resistance across the connecting portion, is greater than the resistance across the first cell. The combined resistance across the first and second channels  1208 ,  1209  is greater than the resistance across the second cell. More specifically, the first cell has a first characteristic resistance. The second cell has a second characteristic resistance. The combined resistance across the first and second channels  1208 ,  1209  is a third characteristic resistance that is greater than the first characteristic resistance across the first cell. The third characteristic resistance is greater than the second characteristic resistance across the second cell. By having a combined resistance across the first and second channels  1208 ,  1209  that is greater than the resistance across the first cell and the second cell, charge is extracted from the first and second terminals, rather than being transferred across between the first cell and the second cell, across the connecting portion. In this particular example, the resistance value of the first characteristic resistance and the value of the second characteristic resistance are the same. It is envisaged that in some examples, the third characteristic resistance across the connecting portion is equal to at least one of the first characteristic resistance and the second characteristic resistance. It is envisaged that more than two channels  1208 ,  1209  may be provided between the first cell and the second cell. By providing multiple channels between the first cell and the second cell, the combined resistance is increased with the number of channels. The space between the channels may be increased to further increase the combined resistance across the connecting portion. In this particular example, the combined resistance across the connecting portion is five times the resistance across the first cell. In this particular example, the resistance across the connecting portion is also five times the resistance across the second cell. The resistance across the first cell and across the second cell are the same in this particular example. 
       FIG.  18    illustrates a two-terminal device  1300 . The two-terminal device  1300  includes a substrate  1302 . The substrate  1302  has a first cell  1304 , a second cell  1306 , a first terminal and a second terminal as previous described with reference to  FIG.  17    and thus will not be described again in detail. Like numerals apply with respect to  FIG.  17   , except in that in  FIG.  18    they begin with the digits “13” instead of “12”. A connecting portion is provided between the first cell  1304  and the second cell  1306 . The connecting portion includes a number of channels. In this particular example, the connecting portion is provided with two channels  1308 ,  1309  that are filled with the third material  1314  as described in relation to  FIG.  17   . As will be noted,  FIG.  18    is identical to that of  FIG.  17   , except in that the channels within the connecting portion are filled, such that an electrical connection is made between the first material  1310  on one side of each channel, and the second material  1312  on the other side of each channel. Thus, an electrical pathway is formed thereacross. 
     In use, the resistance across the connecting portion is greater than the resistance across the first cell  1304 . The resistance across the connecting portion is also greater than the resistance across the second cell  1306 . More specifically, the first cell has a first characteristic resistance. The second cell has a second characteristic resistance. The resistance across the connecting portion is a third characteristic resistance that is greater than the first characteristic resistance across the first cell  1304 . The third characteristic resistance is also greater than the second characteristic resistance across the second cell  1306 . By having an arrangement where the resistance across the connecting portion is greater than the first characteristic resistance across the first cell  1304  and greater than the second characteristic resistance across the second cell  1306 , charge is extracted from the first and second terminals, rather than being transferred across the first and second terminals. In this particular example, the third characteristic resistance is three times the first characteristic resistance across the first cell  1304 . The third characteristic resistance is there times the second characteristic resistance across the second cell  1306 . In some examples, the connecting portion is additionally provided with a resistive element (not shown) that increases the resistance across the connecting portion. 
       FIG.  19    illustrates a two-terminal device  1400 . The two-terminal device  1400  includes a substrate  1402  that has a first cell  1404  and a second cell  1406  substantially as previously described with reference to  FIG.  17   , and therefore will not be described here again in detail. Substrate  1402  is provided with a first terminal and a second terminal substantially as previously described with reference to  FIG.  17   , and therefore will not be described here again in detail. A connecting portion  1408  is provided between the first cell  1404  and the second cell  1406 . In this particular example, the connecting portion  1408  is a planar element extending from and between the first series of grooves forming the first cell  1404  and the second series of groves forming the second cell  1406 . The connecting portion  1408  extends between the first cell  1404  and the second cell  1406  in the direction along the web direction of the substrate  1402 . The first series of grooves include a first face  1404   a , a second, opposing, face  1404   b , and a cavity  1404   c  therebetween. The second series of grooves include a first face  1406   a , a second, opposing, face  1406   b , and a cavity  1406   c  therebetween. The first faces  1404   a ,  1406   a  are coated with a first material  1410 . The second faces  1404   b ,  1406   b  are coated with a second material  1412 . The second material  1412  coating the second face  1404   b  of the groove  1404  proximal the connecting portion  1408  partially coats the connecting portion  1408 . 
     The first material  1410  coating the first face  1406   a  of the groove  1404  proximal the connecting portion  1408  partially coats the connecting portion  1408 . In this way, the connecting portion  1408  provided between the first cell  1404  and the second cell  1406  is partially coated with a second material  1412  on the end of the connecting portion  1408  proximal the first cell  1404 . The connecting portion  1408  provided between the first cell  1404  and the second cell  1406  is partially coated with a first material  1410  on the end of the connecting portion  1408  proximal the second cell  1406 . The connecting portion  1408  is therefore provided between the first cell  1404  and the second cell  1406 , partially coated with a second material  1412  on a first end proximal the first cell  1404 , and is partially coated with a first material  1410  on a second end proximal the second cell  1406 . The first material  1410  and the second material  1412  partially coating the connecting portion  1408  are electrically separated from one another. The connecting portion  1408  ensures an electrical resistance from one side to the other. 
     In use, the resistance across the connecting portion  1408  is greater than the resistance across the first cell  1404 . The resistance across the connecting portion  1408  is greater than the resistance across the second cell  1406 . The first cell  1404  has a first characteristic resistance. The second cell  1406  has a second characteristic resistance. The resistance across the connecting portion  1408  is a third characteristic resistance that is greater than the first characteristic resistance across the first cell  1404 . The third characteristic resistance is greater than the second characteristic resistance across the second cell  1406 . The arrangement of having a greater resistance across the connecting portion  1408  between the first cell  1404  and the second cell  1406  allows charge from the first or second cell to be extracted from the first and second terminals, rather than being transferred between the first cell  1404  and the second cell  1406 , across the connecting portion  1408 . 
       FIG.  20    illustrates a two-terminal device  1500 . The two-terminal device  1500  includes a substrate  1502 . The substrate  1502  has a first cell  1504  and a second cell  1504  spaced apart from the first cell  1504  along the substrate  1502  along the web direction of the substrate  1502 . The first cell  1504  and the second cell  1506  are as previously described with reference to  FIG.  17   , and therefore will not be described here again in detail. The substrate  1502  is provided with a first terminal and a second terminal as described with reference to  FIG.  17   , and therefore will also not be described here again in detail. A connecting portion is provided between the first cell  1504  and the second cell  1506 . The connecting portion includes a channel  1508  provided with a first face  1508   a , a second, opposing, face  1508   b , and a cavity  1508   c  therebetween. The channel  1508  has a depth that is greater than the grooves of each of the first cell  1504  and the second cell  1506 . 
     The first faces  1504   a ,  1506   a ,  1508   a  are coated with a first material  1510 . The second faces  1504   b ,  1506   b ,  1508   b  are coated with a second material  1512 . Additionally, a third material  1514  is provided within the cavities  1504   c ,  1506   c ,  1508   c . The cavities  1504   c ,  1506   c  of the first cell  1504  and second cell  1506  respectively are filled to the extent that the first material  1510  and the second material  1512  on opposing faces ( 1504   a ,  1504   b  and  1506   a ,  1506   b ) are in contact with the third material  1514 . This forms an electrical pathway across the first cell  1504 , and across the second cell  1506 . 
     Unlike the two-terminal device shown in  FIG.  14   , in which the cavity is fully filled by a material  1016 , the walls, formed by faces  1508   a ,  1508   b , of the cavity  1508   c  are coated with the third material  1514 . The coating of the cavity  1508   c  is such that the third material  1514  in the cavity  1508   c  is electrically connected to the first material  1510  on the first face  1508   a , and the second material  1512  on the second face  1508   b . An electrical pathway is therefore provided between the first material  1510  on the first face  1508   a  of the connecting portion  1508 , and the second material  1512  on the second face  1508   b  of the connecting portion  1508 . The channel  1508  creates an electrical connection from one side to the other. That is, the channel  1508  electrically connects one side, proximal the first cell  1504 , from the other side, proximal the second cell  1506 . 
     In use, the resistance across the connecting portion is greater than the resistance across the first cell  1504 . The resistance across the connecting portion is greater than the resistance across the second cell  1506 . The first cell  1504  has a first characteristic resistance. The second cell  1506  has a second characteristic resistance. The resistance across the connecting portion is a third characteristic resistance that is greater than the first characteristic resistance across the first cell  1504 . The third characteristic resistance is greater than the second characteristic resistance across the second cell  1506 . This arrangement allows charge from the first or second cell to be extracted from the first and second terminals, rather than being transferred between the first cell  1504  and the second cell  1506 , across the connecting portion  1508 . 
       FIG.  21    illustrates a two-terminal device  1600 . The two-terminal device  1600  includes a substrate  1602  having a first cell  1604 , a second cell  1606 , a first terminal and a second terminal, as hereinbefore described with reference to  FIG.  20   , and therefore will not be described here again in detail. A connecting portion including channel  1608  is provided between the first cell  1604  and the second cell  1606 . The channel  1608  is provided with a first face  1608   a  proximal the first cell  1604 , and a second, opposing face  1608   b  proximal the second cell  1606 . The channel  1608  is provided with a cavity  1608   c  between the first face  1608   a  and the second face  1608   b . The first face  1608   a  of the channel  1608  and the second face  1608   b  of the channel  1608  extend a depth into the substrate  1602  greater than the depth of the grooves of the first cell  1604  and second cell  1606 . In this particular example, the channel  1608  is substantially U-shaped, having the first face  1608   a , the second face  1608   b , and a bottom rutted portion. In this example, the bottom rutted portion is formed of eight undulations. The cavity  1608   c  of the channel  1608  is larger in size in comparison to the cavities  1604   c ,  1606   c  of the first cell  1604  and the second cell  1606  respectively. The greater size and the depth of the channel  1608  in comparison with the grooves of the first cell  1604  and the second  1606  provide a greater resistance across the connecting portion relative to the resistance across the first cell  1604  and the second cell  1606  respectively. 
     The first faces  1604   a ,  1606   a ,  1608   a  are coated with a first material  1610 . The second faces  1604   b ,  1606   b ,  1608   b  are coated with a second material  1612 . Additionally, a third material  1614  is provided within the cavities  1604   c ,  1606   c ,  1608   c . The cavities  1604   c ,  1606   c  of the first cell  1604  and the second cell  1606  respectively, are filled to the extent that the first material  1610  and the second material  1612  on opposing faces ( 1604   a ,  1604   b  and  1606   a ,  1606   b ) are in contact with the third material  1614 . This forms an electrical pathway across the grooves of the first cell  1604 , and between the grooves of the second cell  1606 . 
     In this particular example, each of the grooves of the bottom rutted portion, forming the cavity  1608   c , is partially filled, for example coated, with the third material  1614 . In this way, the third material  1614  forms a coating, or a conformed coating or a film, of the third material  1614  within the undulations of the channel  1608 . Thus, the third material  1614  is in contact with the first material  1610  on the first face  1608   a . The third material  1614  also contacts the second material  1612  on the second face  1608   b . An electrical pathway is provided between the third material  1614  and the first material  1610  on the first face  1608   a . An electrical pathway is provided between the third material  1614  and the second material  1612  on the second face  1608   b . The connecting portion provides an electrical connection from one side to the other. That is, the connecting portion provides an electrical connection from one side of the connecting portion proximal the first cell  1604 , to the other side of the connecting portion proximal the second cell  1606 . 
     In use, the resistance across the connecting portion is greater than the resistance across the first cell  1604 . The resistance across the connecting portion is also greater than the resistance across the second cell  1606 . The first cell  1604  has a first characteristic resistance. The second cell  1606  has a second characteristic resistance. The resistance across the connecting portion has a third characteristic resistance that is greater than the first characteristic resistance across the first cell  1604 . The third characteristic resistance across the connecting portion is greater than the second characteristic resistance across the second cell  1606 . By having a resistance across the connecting portion that is greater than the resistance across the first cell  1604  and the second cell  1606 , charge from the first or second cell is extracted from the first and second terminals, rather than being transferred across between the first cell  1604  and the second cell  1606 . 
       FIG.  22    illustrates a two-terminal device  1700 . The two-terminal device  1700  includes a substrate  1702 . The substrate  1702  has a first cell  1704  and a second cell  1706  spaced apart from the first cell  1704  along the substrate  1702  along the web direction of the substrate  1702 . The first cell  1704  and the second cell  1706  are as previously described with reference to  FIG.  20   , and therefore will not be described here again in detail. The substrate  1702  is provided with a first terminal and a second terminal. The first and second terminals are formed at opposing edges of the substrate  1702  across the transverse direction of the substrate  1702 . The first and second terminals are electrically connected to the first cell  1704  and the second cell  1706 . That is, the first and second terminals are in electrical communication with each of the first cell  1704  and the second cell  1706 . 
     A connecting portion, including a peak  1708  of the substrate  1702  is provided between the first cell  1704  and the second cell  1706 . The peak  1708  is provided with a first face  1708   a  and a second, opposing, face  1708   b . In this example, the peak  1708  is directed upwards, in a direction opposite to the direction of the grooves of the first cell  1704  and the second cell  1706 . The first face  1708   a  of the peak  1708  is provided on a side proximal the first cell  1704 . The second face  1708   b  of the peak  1708  is provided on a side proximal the second cell  1706 . The peak  1708  has a height that is greater than the depth of the grooves of each of the first cell  1704  and the second cell  1706 . In this particular example, the peak  1708  is formed from a block material. having a first material disposed on the first face  1708   a  and a second material disposed on the second face  1708   b . This first and second materials disposed thereon may be the same as the first and second material  1710 ,  1712  disposed on the faces  1704   a ,  1704   b ,  1706   a ,  1706   b  of the cells  1704 ,  1706  as described below. In particular, the first face  1708   a  may be coated with non-insulating material, such as a conductor. In particular, the second face  1708   b  may be coated with non-insulating material, such as a conductor. There may be a region between the first face  1708   a ,  1708   b  in which no material is provided, such as a gap. This may be provided by removing a portion of the materials provided on the first face  1708   a  and the second face  1708   b . Alternatively, such a portion may be masked during manufacturing. Further, in other embodiments, the upper portion of the block material may be removed after coating the first face  1708   a  and the second face  1708   b , thereby providing an electrical resistance, between the respective faces. In this example, the connecting portion does not have a cavity. The connecting portion includes a peak at an end distal the grooves of the first cell  1704  and the second cell  1706 . 
     The first faces  1704   a ,  1706   a  of the first cell  1704  and second cell  1706  respectively, are coated with a first material  1710 . The second faces  1704   b ,  1706   b  of the first cell  1704  and second cell  1706  respectively, are coated with a second material  1712 . Additionally, a third material  1714  is provided within the cavities  1704   c ,  1706   c  of the first cell  1704  and second cell  1706  respectively. The cavities  1704   c ,  1706   c  are filled to the extent that the first material  1710  and the second material  1712  on opposing faces ( 1704   a ,  1704   b  and  1706   a ,  1706   b ) are in contact with the third material  1714 . This forms an electrical pathway across the first cell  1704 , and across the second cell  1706 . 
     In use, the resistance across the connecting portion is greater than the resistance across the first cell  1704 . The resistance across the connecting portion is greater than the resistance across the second cell  1706 . The first cell  1704  has a first characteristic resistance and the second cell  1706  has a second characteristic resistance. The resistance across the connecting portion is a third characteristic resistance that is greater than the first characteristic resistance across the first cell  1704 . The third characteristic resistance is greater than the second characteristic resistance across the second cell  1706 . This arrangement allows charge from the first or second cell to be extracted from the first and second terminals, rather than being transferred between the first cell  1704  and the second cell  1706 , across the connecting portion. 
       FIG.  23    illustrates a comparison between the two-terminal device described in relation to  FIG.  1    (“parallel first”) and the two-terminal device described in relation to  FIGS.  2 ( a )  and  3  (“series first (with delin)”).  FIG.  23    illustrates the performance of each device as a function of electrical short probability per groove section. The performance of a device is defined as a percentage or a fraction of incoming light energy converted into electrical energy (PCE). As can be seen in  FIG.  23   , the performance of the two-terminal device described in  FIGS.  2 ( a )  and  3  is far superior to that of the two-terminal device described in  FIG.  1   . In particular, the device of  FIGS.  2 ( a )  and  3  remains at a high operational performance even at high short probabilities per groove section. On the other hand, the operational performance of the device of  FIG.  1    rapidly decreases with an increasing short probability per groove section. In this way, the two-terminal device as described herein has a superior performance over the prior art. 
       FIG.  24    illustrates the performance, specifically the fraction of optimal performance with respect to a two-terminal device without a delineation feature, as a function of the resistance of the delineation feature, specifically measured as a multiple of the characteristic resistance of the delineation feature with respect to the characteristic resistance of the adjacent grooves, for a two-terminal device described herein. As shown in  FIG.  24   , as the characteristic resistance of the delineation feature, that is the connecting portion, is increased with respect to the characteristic resistance of the adjacent grooves, the performance of the device tends towards the expected ideal performance. 
       FIG.  25    illustrates the performance, specifically the fraction of optimal performance with respect to a two-terminal device without a delineation feature, as a function of the delineation short-circuit current, as a fraction of the current within a series of grooves. In particular, as described herein, the delineation feature acts as a reverse biased diode, and so the open-circuit voltage created is unimportant, as the operating voltage flows in the opposite direction. This is shown by the linear relationship between these functions, as demonstrated in  FIG.  25   . 
     It will be appreciated by persons skilled in the art that the above embodiment(s) have been described by way of example only and not in any limitative sense, and that various alterations and modifications are possible without departing from the scope of the invention as defined by the appended claims. Various modifications to the detailed designs as described above are possible, for example, variations may exist in number, shape, size, arrangement, assembly or the like. For example, any number of grooves and any number of series of grooves may be used, any number of channels, or delineation features, may be used. Further, the channel(s) may intersect the grooves at any appropriate angle and may be shaped in any appropriate way. Further, various grooves, channels, connecting portions or the like may be partially filled, filled, completely filled, or coating, as described herein. Mere reference to coating or filling in one embodiment does not preclude the possibility of filling or coating, respectively, the feature of said embodiment.