Patent ID: 12249664

DETAILED DESCRIPTION

Photovoltaic devices can be formed from a stack of functional layers formed over a substrate. One or more of the functional layers can include a thin film of material, i.e., the photovoltaic device can be a thin film photovoltaic device. Thin film photovoltaic devices can include an absorber layer for converting light into charge carriers, and conductive layers for collecting the charge carriers. In some instances, a conducting layer can be formed towards an back side of the module with respect to the absorber layer. In single junction devices, the conductive layer can be disposed at the back side of the module and can use non-transparent metal layers as constituents. However, such non-transparent layers may be unsuitable for use as a conducting layer disposed between junctions in multi junction photovoltaic devices or tandem photovoltaic devices. The embodiments provided herein relate to transparent conductive layers and photovoltaic devices including the same. The disclosed transparent conductive layers can improve reliability and durability of current collecting portions of photovoltaic devices, while allowing the use of the photovoltaic devices in applications that require transparency, like windows, skylights, and tandem devices.

Referring now toFIG.1, an embodiment of a photovoltaic device100is schematically depicted. The photovoltaic device100can be configured to receive light and transform light into electrical energy, e.g., photons can be absorbed from the light and transformed into electrical current via the photovoltaic effect. Thus, for sake of discussion and clarity, the photovoltaic device100can define a front side102configured to face a primary light source such as, for example, the sun. Additionally, the photovoltaic device100can also define a back side104offset from the front side102such as, for example, by a plurality of functional layers of material. It is noted that the term “light” can refer to various wavelengths of the electromagnetic spectrum such as, but not limited to, wavelengths in the ultraviolet (UV), infrared (IR), and visible portions of the electromagnetic spectrum. “Sunlight,” as used herein, refers to light emitted by the sun.

The photovoltaic device100can include a plurality of layers disposed between the front side102and the back side104. As used herein, the term “layer” refers to a thickness of material provided upon a surface. Each layer can cover all or any portion of an adjacent surface. In some embodiments, the layers of the photovoltaic device100can be divided into an array of photovoltaic cells200. For example, the photovoltaic device100can be scribed according to a plurality of serial scribes202and a plurality of parallel scribes204. The serial scribes202can extend along a length Y of the photovoltaic device100and demarcate the photovoltaic cells200along the length Y of the photovoltaic device100. Neighboring cells of the photovoltaic cells200can be serially connected along a width X of the photovoltaic device100. In other words, a monolithic interconnect of the neighboring cells200can be formed, i.e., adjacent to the serial scribe202. The parallel scribes204can extend along the width X of the photovoltaic device100and demarcate the photovoltaic cells200along the width X of the photovoltaic device100. Under operations, current205can predominantly flow along the width X through the photovoltaic cells200serially connected by the serial scribes202. Under operations, parallel scribes204can limit the ability of current205to flow along the length Y. Parallel scribes204are optional and can be configured to separate the photovoltaic cells200that are connected serially into groups206arranged along length Y.

Referring still toFIG.1, the parallel scribes204can electrically isolate the groups206of photovoltaic cells200that are connected serially. In some embodiments, the groups206of the photovoltaic cells200can be connected in parallel such as, for example, via electrical bussing. Optionally, the number of parallel scribes204can be configured to limit a maximum current generated by each group206of the photovoltaic cells200. In some embodiments, the maximum current generated by each group206can be less than or equal to about 200 milliamps (mA) such as, for example, less than or equal to about 100 mA in one embodiment, less than or equal to about 75 mA in another embodiment, or less than or equal to about 50 mA in a further embodiment.

Referring now toFIG.2, the layers of the photovoltaic device100can include a thin film stack provided over a substrate110. The substrate110can be configured to facilitate the transmission of light into the photovoltaic device100. The substrate110can be disposed at the front side102of the photovoltaic device100. Referring collectively toFIGS.2and3, the substrate110can have a first surface112substantially facing the front side102of the photovoltaic device100and a second surface114substantially facing the back side104of the photovoltaic device100. One or more layers of material can be disposed between the first surface112and the second surface114of the substrate110.

Referring toFIG.3, the substrate110can include a transparent layer120having a first surface122substantially facing the front side102of the photovoltaic device100and a second surface124substantially facing the back side104of the photovoltaic device100. In some embodiments, the second surface124of the transparent layer120can form the second surface114of the substrate110. The transparent layer120can be formed from a substantially transparent material such as, for example, glass. Suitable glass can include soda-lime glass, or any glass with reduced iron content. The transparent layer120can have any suitable transmittance range, including about 250 nm to about 1,300 nm in some embodiments. The transparent layer120may also have any suitable transmittance percentage, including, for example, more than about 50% in one embodiment, more than about 60% in another embodiment, more than about 70% in yet another embodiment, more than about 80% in a further embodiment, or more than about 85% in still a further embodiment. In one embodiment, transparent layer120can be formed from a glass with about 90% transmittance, or more. Optionally, the substrate110can include a coating126applied to the first surface122of the transparent layer120. The coating126can be configured to interact with light or to improve durability of the substrate110such as, but not limited to, an antireflective coating, an antisoiling coating, or a combination thereof.

Referring again toFIG.2, the photovoltaic device100can include a barrier layer130configured to mitigate diffusion of contaminants (e.g., sodium) from the substrate110, which could result in degradation or delamination of other layers of the photovoltaic stack. The barrier layer130can have a first surface132substantially facing the front side102of the photovoltaic device100and a second surface134substantially facing the back side104of the photovoltaic device100. In some embodiments, the barrier layer130can be provided adjacent to the substrate110. For example, the first surface132of the barrier layer130can be provided upon the second surface114of the substrate100. The phrase “adjacent to,” as used herein, means that two layers are disposed contiguously and without any intervening materials between at least a portion of the layers.

Generally, the barrier layer130can be substantially transparent, thermally stable, with a reduced number of pin holes and having high sodium-blocking capability, and good adhesive properties. Alternatively or additionally, the barrier layer130can be configured to apply color suppression to light. The barrier layer130can include one or more layers of suitable material, including, but not limited to, tin oxide, silicon dioxide, aluminum-doped silicon oxide, silicon oxide, silicon nitride, or aluminum oxide. The barrier layer130can have any suitable thickness bounded by the first surface132and the second surface134, including, for example, more than about 100 Å in one embodiment, more than about 150 Å in another embodiment, or less than about 200 Å in a further embodiment.

Referring still toFIG.2, the photovoltaic device100can include a transparent conductive oxide (TCO) layer140configured to provide electrical contact to transport charge carriers generated by the photovoltaic device100. The TCO layer140can have a first surface142substantially facing the front side102of the photovoltaic device100and a second surface144substantially facing the back side104of the photovoltaic device100. In some embodiments, the TCO layer140can be provided adjacent to the barrier layer130. For example, the first surface142of the TCO layer140can be provided upon the second surface134of the barrier layer130. Generally, the TCO layer140can be formed from one or more layers of n-type semiconductor material that is substantially transparent and has a wide band gap. Specifically, the wide band gap can have a larger energy value compared to the energy of the photons of the light, which can mitigate undesired absorption of light. The TCO layer140can include one or more layers of suitable material, including, but not limited to, tin dioxide, doped tin dioxide (e.g., F—SnO2), indium tin oxide, or cadmium stannate (Cd2SnO4). In embodiments where the TCO layer140comprises cadmium stannate, the cadmium stannate can be provided in a crystalline form. For example, the cadmium stannate can be deposited as a film and then subjected to an annealing process, which transforms the thin film into a crystallized film.

The photovoltaic device100can include a buffer layer150configured to provide an insulating layer between the TCO layer140and any adjacent semiconductor layers. The buffer layer150can have a first surface152substantially facing the front side102of the photovoltaic device100and a second surface154substantially facing the back side104of the photovoltaic device100. In some embodiments, the buffer layer150can be provided adjacent to the TCO layer140. For example, the first surface152of the buffer layer150can be provided upon the second surface144of the TCO layer140. The buffer layer150can include material having higher resistivity than the TCO later 140, including, but not limited to, intrinsic tin dioxide, zinc magnesium oxide (e.g., Zn1−xMgxO), silicon dioxide (SiO2), aluminum oxide (Al2O3), aluminum nitride (AlN), zinc tin oxide, zinc oxide, tin silicon oxide, or any combination thereof. In some embodiments, the material of the buffer layer150can be configured to substantially match the band gap of an adjacent semiconductor layer (e.g., an absorber). The buffer layer150may have any suitable thickness between the first surface152and the second surface154, including, for example, more than about 100 Å in one embodiment, between about 100 Å and about 800 Å in another embodiment, or between about 150 Å and about 600 Å in a further embodiment.

Referring still toFIG.2, the photovoltaic device100can include an absorber layer160configured to cooperate with another layer and form a p-n junction within the photovoltaic device100. Accordingly, absorbed photons of the light can free electron-hole pairs and generate carrier flow, which can yield electrical energy. The absorber layer160can have a first surface162substantially facing the front side102of the photovoltaic device100and a second surface164substantially facing the back side104of the photovoltaic device100. A thickness of the absorber layer160can be defined between the first surface162and the second surface164. The thickness of the absorber layer160can be between about 0.5 μm to about 10 μm such as, for example, between about 1 μm to about 7 μm in one embodiment, or between about 1.5 μm to about 4 μm in another embodiment.

According to the embodiments described herein, the absorber layer160can be formed from a p-type semiconductor material having an excess of positive charge carriers, i.e., holes or acceptors. The absorber layer160can include any suitable p-type semiconductor material such as group II-VI semiconductors such as, for example, cadmium and tellurium. Further examples include, but are not limited to, semiconductor materials comprising cadmium, zinc, tellurium, selenium, or any combination thereof. In some embodiments, the absorber layer160can include ternaries of cadmium, selenium and tellurium (e.g., CdSexTe1−x), or a compound comprising cadmium, selenium, tellurium, and one or more additional element (e.g., CdZnSeTe). The absorber layer160may further comprise one or more dopants. The photovoltaic devices100provided herein may include a plurality of absorber materials.

In embodiments where the absorber layer160comprises tellurium and cadmium, the average atomic percent of the tellurium in the absorber layer160can be greater than or equal to about 25 atomic percent and less than or equal to about 50 atomic percent such as, for example, greater than about 30 atomic percent and less than about 50 atomic percent in one embodiment, greater than about 40 atomic percent and less than about 50 atomic percent in a further embodiment, or greater than about 47 atomic percent and less than about 50 atomic percent in yet another embodiment. Alternatively or additionally, average atomic percent of the tellurium in the absorber layer160can be greater than about 45 atomic percent such as, for example, greater than about 49% in one embodiment. It is noted that the average atomic percent described herein is representative of the entirety of the absorber layer160, the atomic percentage of material at a particular location within the absorber layer160can be graded through the thickness compared to the overall composition of the absorber layer160. For example, the absorber layer160can have a graded composition.

In embodiments where the absorber layer160comprises selenium and tellurium, the average atomic percent of the selenium in the absorber layer160can be greater than 0 atomic percent and less or equal to than about 25 atomic percent such as, for example, greater than about 1 atomic percent and less than about 20 atomic percent in one embodiment, greater than about 1 atomic percent and less than about 15 atomic percent in another embodiment, or greater than about 1 atomic percent and less than about 8 atomic percent in a further embodiment. It is noted that the concentration of tellurium, selenium, or both can be graded through the thickness of the absorber layer160. For example, when the absorber layer160comprises a compound including selenium at a mole fraction of x and tellurium at a mole fraction of 1−x (SexTe1−x), x can vary in the absorber layer160with distance from the first surface162of the absorber layer160.

Referring still toFIG.2, the absorber layer160can be doped with a dopant configured to manipulate the charge carrier concentration. In some embodiments, the absorber layer160can be doped with a Group V dopant such as, for example, arsenic, phosphorous, antimony, or a combination thereof. Alternatively or additionally, the absorber layer160can be doped with a Group IB dopant such as, for example, copper, silver, gold, or a combination thereof. The total density of the dopant within the absorber layer160can be controlled. Moreover, the amount of the dopant can vary with distance from the first surface162of the absorber layer160.

According to the embodiments provided herein, the p-n junction can be formed by providing the absorber layer160sufficiently close to a portion of the photovoltaic device100having an excess of negative charge carriers, i.e., electrons or donors. In some embodiments, the absorber layer160can be provided adjacent to n-type semiconductor material. Alternatively, one or more intervening layers can be provided between the absorber layer160and n-type semiconductor material. In some embodiments, the absorber layer160can be provided adjacent to the buffer layer150. For example, the first surface162of the absorber layer160can be provided upon the second surface154of the buffer layer150.

The photovoltaic device100can include a back contact layer170configured to mitigate undesired alteration of the dopant and to provide electrical contact to the absorber layer160. The back contact layer170can have a first surface172substantially facing the front side102of the photovoltaic device100and a second surface174substantially facing the back side104of the photovoltaic device100. A thickness of the back contact layer170can be defined between the first surface172and the second surface174. The thickness of the back contact layer170can be between about 5 nm to about 200 nm such as, for example, between about 10 nm to about 50 nm in one embodiment.

In some embodiments, the back contact layer170can be provided adjacent to the absorber layer160. For example, the first surface172of the back contact layer170can be provided upon the second surface164of the absorber layer160. In some embodiments, the back contact layer170can include combinations of materials from Groups I, II, VI, such as for example, one or more layers containing zinc and tellurium in various compositions. Further exemplary materials include, but are not limited to, a bilayer of cadmium zinc telluride and zinc telluride, or zinc telluride doped with a group V dopant such as, for example, nitrogen. A thin film junction176can be defined as the thin film stack primarily contributing to the photovoltaic effect. For example, in some embodiments, the thin film junction176can include the transparent conductive oxide layer140, the buffer layer150, the absorber layer160, the back contact layer170, or combinations thereof.

Referring collectively toFIGS.2, and4, the photovoltaic device100can include a transparent conducting layer180configured to provide electrical contact with the back contact layer170, the absorber layer160, or both. The transparent conducting layer180can have a first surface182substantially facing the front side102of the photovoltaic device100and a second surface184substantially facing the back side104of the photovoltaic device100. In some embodiments, the transparent conducting layer180can be provided adjacent to the back contact layer170or the absorber layer160. For example, the first surface182of the transparent conducting layer180can be provided upon the second surface174of the back contact layer170or the second surface162of the absorber layer160. A thickness of the transparent conducting layer180can be defined between the first surface182and the second surface184. The thickness of the transparent conducting layer180can be less than about 500 nm such as, for example, between about 40 nm and about 400 nm in one embodiment, or between about 60 nm and about 350 nm.

According to the embodiments provided herein, the transparent conducting layer180can include one or more functional layers of material. In some embodiments, the conducting layer180can have an average transmittance greater than about 50% to light having a wavelength between 300 nm and 1300 nm. Optionally, the conducting layer180can have an average transmittance greater than about 50% to light having a wavelength 800 nm to 1300 nm such as, for example, greater than about 85% in one embodiment, or greater than about 90% in another embodiment, or greater than about 95% in further embodiment. The transparent conducting layer180can include a diffusion barrier layer210operable to limit diffusion of metal species into active areas of the cell200such as, for example, the absorber layer160. Diffusion of metal species into the absorber layer160can degrade conversion efficiency of the cell200. Such degradation and decreased performance can be particularly associated with hot and/or humid environments. Accordingly, the use of a suitable diffusion barrier210can improve performance of the photovoltaic device100.

The diffusion barrier layer210can have a first surface212substantially facing the front side102of the photovoltaic device100and a second surface214substantially facing the back side104of the photovoltaic device100. A thickness of the diffusion barrier layer210can be defined between the first surface212and the second surface214. The thickness of the diffusion barrier layer210can be less than about 125 nm such as, for example, between about 2 nm and about 100 nm in one embodiment, or between about 5 nm and about 50 nm in another embodiment.

In some embodiments, the diffusion barrier layer210can be provided adjacent to the back contact layer170. For example, the first surface212of the diffusion barrier layer210can be provided upon the second surface174of the back contact layer170. Thus, in some embodiments, the first surface182of the back contact layer180can be formed by the first surface212of the diffusion barrier layer210. Generally, the diffusion barrier layer210can be formed by a material with suitable transmittance capable of being doped “+” type. For example, charge densities of greater than about 1×1016cm−3can be considered to be “+” type. In some embodiments, the diffusion barrier layer210can be doped n+. In alternative embodiments, the the diffusion barrier layer210can be doped p+. Although the boundaries are not rigid, a material can be considered n-type if electron donor carriers are present in the range of about 1×1011cm−3to about 1×1016cm−3, and n+ type if donor carrier density is greater than about 1×1016cm−3. Similarly, a material is generally considered p-type if electron acceptor carriers (i.e. “holes”) are present in the range of about 1×1011cm−3to about 1×1016cm−3, and p+ type if acceptor carrier density is greater than about 1×1016cm−3. The boundaries are not rigid and may overlap because a layer may be p+ relative to a layer that is p-type (or n+ relative to a layer that is n-type) if the carrier concentration is at least two orders of magnitude (i.e. 100-fold) higher, regardless of the absolute carrier density. Additionally, charge densities of greater than about 1×1018cm−3can be considered to be “++” type; and thus a layer of either n-type or p-type can be “++” relative to a layer of the same type that is itself “+” relative to yet a third layer, if the ++ layer has a same-type carrier density more than 100 fold that of the + layer.

Suitable materials for the diffusion barrier layer210can include refractory oxy-nitrides such as, for example, titanium oxy-nitrides (TiNxOy) or molybdenum oxy-nitrides (MoNxOy). Without being bound to theory, applicant has discovered that oxy-nitrides can exhibit improved optical properties, i.e., increased transmittance, with increased amounts of oxygen in the alloys. However, it is further believed that the electrical conductivity can degrade with the increased oxygen. Another group of materials suitable for use in the transparent diffusion barrier310include are transparent conductive oxides such as, for example, tin oxide (SnO2) zinc oxide (ZnO), indium-tin oxide (In(2−x)SnxO3), cadmium oxide (CdO), and cadmium stannate (Cd2SnO4). These transparent conductive oxides can be doped with impurities such as F, Al, In, Ga, Ti, and others to alter their electrical and optical properties.

Unexpectedly, it was discovered that cadmium stannate (Cd2SnO4) demonstrated a superior combination of diffusion-blocking, optical properties, and electrical properties relative to other transparent conductive oxides. It was further discovered that amorphous cadmium stannate can be utilized for the diffusion barrier layer210. As used herein, the term “amorphous” refers to a solid that lacks a long range order. Generally, amorphous cadmium stannate can be formed by depositing a layer of material without converting the morphology of the layer via a heat treatment process. For example, the amorphous cadmium stannate can be deposited at relatively low temperatures and without annealing after deposition. In some embodiment, amorphous cadmium stannate can be formed from CdxSnO4material where 0.5≤x≤2.

Referring still toFIGS.2and4, the transparent conducting layer180can include a high conductivity layer220configured to provide low device series resistance. The high conductivity layer220can have a first surface222substantially facing the front side102of the photovoltaic device100and a second surface224substantially facing the back side104of the photovoltaic device100. A thickness of the high conductivity layer220can be defined between the first surface222and the second surface224. The thickness of the high conductivity layer220can be less than about 300 nm such as, for example, between about 30 nm and about 300 nm in one embodiment, between about 50 nm and about 250 nm in another embodiment, or between about 100 nm and about 250 nm in a further embodiment.

In some embodiments, the high conductivity layer220can be positioned further away from the absorber layer160or the back contact layer170relative to the diffusion barrier layer210. Accordingly, the diffusion barrier layer210can be positioned between the absorber layer160and the high conductivity layer220or the back contact layer170and the high conductivity layer220. Specifically, in some embodiments, the high conductivity layer220can be provided adjacent to the high-conductivity layer. For example, the first surface222of the high conductivity layer220can be provided upon the second surface214of the diffusion barrier layer210. Generally, the high conductivity layer220can be formed by a material with suitable transmittance capable of being doped “++” type. In some embodiments, the diffusion barrier layer210can be doped n++. Accordingly, the high conductivity layer220can include a degneratively doped transparent conductive oxide. In some embodiments, the high conductivity layer220can be doped n++ intrinsically or with an oxide dopant. Suitable oxide dopants include, but are not limited to, In2O3, Ga2O3, TiO2, Dy2O3, SnO2, Y2O3, Al2O3, or any combination thereof. Applicants discovered that cadmium oxide (CdO) such as, for example, indium oxide doped cadmium oxide (CdO:In2O3) or gallium oxide doped cadmium oxide (CdO:Ga2O3) had relatively high electrical mobility compared to other transparent conductive oxides of suitable optical properties. Accordingly, embodiments of the high conductivity layer220including cadmium oxide demonstrated a relatively high fill factor, and improved photovoltaic performance.

According to the embodiments provided herein, the transparent conducting layer180can include a capping layer230operable to mitigate corrosion of the high conductivity layer220in hot and humid environments. The capping layer230can have a first surface232substantially facing the front side102of the photovoltaic device100and a second surface234substantially facing the back side104of the photovoltaic device100. A thickness of the capping layer230can be defined between the first surface232and the second surface234. The thickness of the capping layer230can be less than about 125 nm such as, for example, between about 2 nm and about 100 nm in one embodiment, or between about 5 nm and about 50 nm in another embodiment.

In some embodiments, the capping layer230can be positioned further away from the absorber layer160or the back contact layer170relative to the high conductivity layer220. Accordingly, the high conductivity layer220can be positioned between the diffusion barrier layer210and the capping layer230. Specifically, in some embodiments, the capping layer230can be provided adjacent to the high conductivity layer220. For example, the first surface232of the capping layer230can be provided upon the second surface224of the high conductivity layer220. The capping layer230can include a transparent conductive oxide, such as, for example, cadmium stannate. In some embodiments, the capping layer can include amorphous cadmium stannate.

Referring again toFIG.2, the photovoltaic device100can include a back support190configured to cooperate with the substrate110to form a housing for the photovoltaic device100. The back support190can be disposed at the back side104of the photovoltaic device100. The back support190can include any suitable material, including, for example, borosilicate glass, float glass, soda lime glass, carbon fiber, or polycarbonate. Alternatively, the back support190may be any suitable material such as a polymer-based back sheet. The back support190and substrate110can protect the various layers of the photovoltaic device100from exposure to moisture and other environmental hazards.

Referring toFIG.5, a tandem photovoltaic device300is schematically depicted. The tandem photovoltaic device300can include a tandem cell302, which can be formed via scribing as disclosed above with respect to the photovoltaic cells200of the photovoltaic device100. The tandem cell300can include the thin film junction176. The thin film junction176can be electrically connected via the transparent conducting layer180and, optionally, an electrical bus236, to a second junction310. As used herein, the phrase “electrically connected” can mean that constituents cooperate to form a substantially ohmic contact directly with one another or indirectly via one or more additional components. Accordingly, current can flow between the second junction310and the thin film junction176via the electrical connection. In some embodiments, the second junction310and the thin film junction176can be electrically connected in series. Alternatively, the second junction310and the thin film junction176can be electrically connected in parallel such as, for example, via one or more additional components or conductors. In some embodiments, the thin film junction176can be positioned nearer to the front side102of the tandem photovoltaic device300than the second junction310. The transparent conducting layer180can be positioned between the thin film junction176and the second junction310.

The second junction310can be configured to convert light into electrical energy via the photovoltaic effect. The second junction310can include a different semiconductor than the absorber layer160of the thin film junction176such as, for example, amorphous silicon (a-Si), crystalline silicon (c-Si), or copper indium gallium selenide (CIGS). The thin film junction176and the second junction310can be configured to absorb different ranges of wavelengths. For example, the thin film junction176can be configured to absorb shorter wavelengths of light than the second junction310. In some embodiments, the average quantum efficiency between 800 nm and 1,300 nm of the thin film junction176can be less than about 20% such as, for example, less than about 10% in one embodiment, or less than about 5% in another embodiment. Additionally, the average quantum efficiency between 800 nm and 1,300 nm of the second junction310can be greater than about 50% such as, for example, greater than about 60% in one embodiment, or greater than about 65% in another embodiment.

It should now be understood that the functional layers of the transparent conducting layer can provide improved transmittance of light, while providing comparable electrical functionality and reliability relative to known non-transparent electrical contacts. Accordingly, the embodiments provided herein can improve the utility of photovoltaic devices. For example, a stack of the diffusion barrier, the high conductivity layer, and the capping layer described herein can be used as a tunnel junction in a tandem photovoltaic device. Alternatively, a stack of the diffusion barrier, the high conductivity layer, and the capping layer described herein can be used as a transparent back electrical contact for a transparent module or for a bifacial module.

According to embodiments described herein, a tandem photovoltaic device can include a thin film junction, a second junction, and a transparent conducting layer. The thin film junction can include an absorber layer including cadmium and tellurium. The second junction can be electrically connected with the thin film junction. Current can flow between the second junction and the thin film junction. The transparent conducting layer can be disposed between the thin film junction and the second junction. The current can flow through the transparent conducting layer. The transparent conducting layer can include a high conductivity layer and an adjacent layer. The high conductivity layer can include cadmium oxide doped “++” type intrinsically or with an oxide dopant. The adjacent layer that is in contact with the high conductivity layer.

In another embodiment, a tandem photovoltaic device can include a thin film junction, a second junction, and a transparent conducting layer. The thin film junction can include an absorber layer including cadmium and tellurium. The second junction can be electrically connected with the thin film junction. Current can flow between the second junction and the thin film junction. The transparent conducting layer can be disposed between the thin film junction and the second junction. The current can flow through the transparent conducting layer. The transparent conducting layer can include a high conductivity layer and an adjacent layer. The high conductivity layer can be doped n++. The adjacent layer is in contact with the high conductivity layer. The adjacent layer comprises amorphous cadmium stannate.

In yet another embodiment, a tandem photovoltaic device can include a thin film junction, a second junction, and a transparent conducting layer. The thin film junction can include an absorber layer including cadmium and tellurium. The second junction can be electrically connected with the thin film junction. Current can flow between the second junction and the thin film junction. The transparent conducting layer can be disposed between the thin film junction and the second junction. The current can flow through the transparent conducting layer. The transparent conducting layer can include amorphous cadmium stannate.

In a further embodiment, a photovoltaic device can include a thin film junction and a transparent conducting layer. The thin film junction can include an absorber layer including cadmium and tellurium. The transparent conducting layer can form at least a part of a series connection with the thin film junction. The transparent conducting layer can include a high conductivity layer and an adjacent layer. The high conductivity layer can be doped “++” type. The adjacent layer can be in contact with the high conductivity layer.

In another embodiment, photovoltaic device can include a thin film junction and a transparent conducting layer. The thin film junction can include an absorber layer including cadmium and tellurium. The transparent conducting layer can form at least a part of a series connection with the thin film junction. The transparent conducting layer can include a high conductivity layer and an adjacent layer. The high conductivity layer can include indium oxide doped cadmium oxide. The adjacent layer can be in contact with the high conductivity layer. The adjacent layer can include cadmium stannate.

In yet another embodiment, a photovoltaic device can include a thin film junction and a transparent conducting layer. The transparent conducting layer can conduct charge carriers from the thin film junction. The transparent conducting layer can include a high conductivity layer and an adjacent layer. The adjacent layer can be in contact with the high conductivity layer. The high conductivity layer comprises indium oxide doped cadmium oxide.

It is noted that the terms “substantially” and “about” may be utilized herein to represent the inherent degree of uncertainty that may be attributed to any quantitative comparison, value, measurement, or other representation. These terms are also utilized herein to represent the degree by which a quantitative representation may vary from a stated reference without resulting in a change in the basic function of the subject matter at issue.

While particular embodiments have been illustrated and described herein, it should be understood that various other changes and modifications may be made without departing from the spirit and scope of the claimed subject matter. Moreover, although various aspects of the claimed subject matter have been described herein, such aspects need not be utilized in combination. It is therefore intended that the appended claims cover all such changes and modifications that are within the scope of the claimed subject matter.