Patent Application: US-200913133127-A

Abstract:
the presently disclosed subject matter describes a new sealing process of a specific type of photovoltaic cells named dye - sensitized solar cells . currently , the sealing of these cells is made by means of a polymer , which connects the two electrode substrates made of glass , isolating the cell &# 39 ; s inner content from the outside . the glass - based sealing method has the advantage of enhancing the cell &# 39 ; s lifetime . however , glass sealing should not lead to the heating of the whole cell , which may cause its degradation . the process here unveiled employs a string of a glass precursor , a powder or a paste , that bounds the cell &# 39 ; s entire external perimeter . the glass precursor string is then heated to its melting point with a laser beam , allowing the two substrates of the cell to stick together .

Description:
sealing plays an important role in the stability / aging of dscs because it makes the cell &# 39 ; s inner components isolated from external contaminants and avoids the loss of important chemicals . the ideal sealing material should be : i ) stable at working conditions — under great solar irradiance and outdoor ambient conditions ; ii ) inert to all the chemical components of the cell , mainly the electrolyte redox couple ; iii ) impermeable to the cell &# 39 ; s chemical compounds and to the atmospheric oxygen and moisture , as well as to other atmospheric contaminants ; iv ) an electric insulator ; v ) a low - cost material and vi ) suitable for simple deposition , which does not affect the correct operation of the cell . the fabrication method of dscs is well known and is described in many bibliographic references [ 3 ][ 14 ][ 24 ][ 26 ][ 27 ][ 28 ] . two sheets of glass coated with an electric conducting material ( p . e . sno 2 : f ), usually denoted as tco ( transparent conducting oxide ), are used as substrates for both the photoelectrode and the counter - electrode . the coated glass plates have high optical transmission (& gt ; 80 %) and low ohmic resistance (& lt ; 10ω ). in the photoelectrode a layer of tio 2 paste is applied and sintered at 450 ° c . on the other hand , the counter - electrode is heated to a temperature between 385 ° c . and 420 ° c ., for about 20 to 30 minutes , allowing the sintering of the catalyst . an electric current collector grid is also deposited onto the glass substrates in order to harvest the produced power . after all these steps , the photoelectrode is sealed together with the counter - electrode . the sealing process here unveiled is performed by the deposition of a glass string on a grooved perimeter at the cell &# 39 ; s photoelectrode . the furrow facilitates the deposition of the glass precursor and ensures a greater mechanical stability across the sealing area . in this area , the tco can be removed to make the sealing process more effective . the glass precursor deposition is performed after print - screening the titanium dioxide . after sintering the titanium dioxide , the temperature is maintained at a certain desired level , but not above the maximum resistance limit of all components of the electrodes [ 15 ][ 29 ] . therefore , the photoelectrode is cooled down to a temperature close to that of the counter - electrode , between 385 ° c . and 420 ° c . the sealing glass precursor , at room temperature , is then deposited over the photoelectrode &# 39 ; s glass sheet and the adhesion process between the sealant material and the electrode substrate starts . the counter - electrode , coated with the catalyst and the current collector grid , is placed on top of the photoelectrode glass substrate at a high temperature . the tco can also be removed in the sealing perimeter of the counter - electrode . the initial heating of both glass substrates , caused by the semiconductor and the platinum catalyst sintering step , facilitates the glass precursor adhesion to the mentioned glass sheets . this dsc manufacturing process optimization avoids a long heating step suggested in patent wo / 2007 / 067402 . the union of the photoelectrode and the counter - electrode is made in such a way that allows the two electrodes to be spaced by a predefined constant distance along the entire sealing perimeter , normally achieved with a metallic frame . in order to perform the soldering process with permanent adhesion of the sealant glass precursor to the glass sheets of the two electrodes it is necessary that , after the contact between the two glass sheets , the temperature raises up to the soldering temperature . however , the cell &# 39 ; s inner components cannot be destroyed . this extra temperature raise is then achieved by using a laser that strikes the counter - electrode perpendicularly . when crossing the counter - electrode , the beam strikes the glass precursor string causing its fusion and avoiding the over - heating of the remaining part of the cell . the sealing glass precursor must have some particular features including a low melting point . the electrodes glass has a melting point between 1000 ° c . and 1200 ° c . [ 30 ] , depending on its composition . however , it is possible to obtain glass with much lower melting points ( between 350 ° c . and 700 ° c .) and lower melting points ( 650 ° c . and 990 ° c .) [ 31 ] . the glass precursor deposition can be performed in two ways : using a glass paste [ 31 ][ 32 ] or a glass powder [ 31 ] . the first strategy is based on a simple deposition method but has the disadvantage of possible contamination of the cell . the contaminants can be removed using a nitrogen flow through the holes performed in the counter - electrode — fig2 . in order to achieve an effective soldering of the glass string to the glass substrate by the laser beam , the laser has to emit a radiation with wavelength at which the glass string is opaque . this strategy allows that the laser beam crosses the counter - electrode and heats the glass string , according to a temperature program advised by the glass manufacturer . on the other hand , if the sealing glass has a quite low melting point , the glass does not need to be fully opaque to the laser beam since even a low or a medium absorbance level is enough to cause the desired heating . after soldering the electrodes , the cell should cool down , after what the dye and the electrolyte are introduced in the cell through the small holes in the counter - electrode side [ 26 ] . these holes need to be closed after the entire addition of the cell &# 39 ; s components . for that , a small amount of glass sealing precursor is deposited over the holes and the subsequent fusion using a laser beam is performed . in this step is better to use a glass opaque to the laser beam wavelength . it also important to mention that the thermal expansion coefficients of the sealing glass precursor and the electrodes &# 39 ; glass should be quite similar , i . e . about ( 8 . 6 − 9 . 2 )× 10 − 6 /° c . ( in the temperature range of 50 ° c . to 350 ° c .). example 1 — dsc sealing with a glass paste of very low melting point this example shows the use of a specific kind of glass precursor and the respective application strategy . the selected glass sealing precursor is an aluminum - borosilicate which contains lead . it has a melting point of 566 ° c . and a medium viscosity of 10 3 pa · s . a string of this glass paste , with a diameter of 1 mm , was applied along the external perimeter of a dsc with 7 cm long and 5 cm wide . in the photoelectrode glass substrate was created a small incision for a better definition of the glass paste string . after sintering the titanium dioxide semiconductor deposited onto the photoelectrode glass plate , this was quickly heated from 450 ° c . up to 520 ° c ., at a rate of 10 ° c . per minute . the sealing glass precursor is immediately deposited along the entire incision made at the glass plate kept at 520 ° c . a constant temperature period , between 385 ° c . and 420 ° c ., should be achieved after the deposition . this cooling step is crucial to avoid an overheating of the counter - electrode when it contacts the photoelectrode glass substrate . the counter - electrode , also prepared with an incision along the soldering line , was then placed on top of the photoelectrode at a temperature of 385 ° c . a small aluminum frame guarantees a constant 30 μm distance between the photoelectrode and counter - electrode glass sheets . from the counter - electrode &# 39 ; s side , a 120 w medium power laser diode of 1064 nm wavelength strikes perpendicularly the sealing glass precursor . the laser beam passes through the dsc perimeter several times until all the gas bubbles formed during the glass fusing process disappear and , consequently , the correct soldering of the cell takes place . at the end of the procedure the cell is left to cool down to room temperature , while a nitrogen flow is used to remove potential contaminants introduced during the sealing process . this nitrogen flow was introduced in the cell through the holes previously made in the counter - electrode glass plate for the subsequent introduction of dye and electrolyte . example 2 — dsc sealing with a glass paste of low melting point and absorption at 1100 nm this example shows the use of a glass precursor of low melting point and opaque to infra - red radiation . the glass precursor paste is a silicate that contains iron oxide ( fe 2 o 3 ), has no lead compounds , has a melting point of about 990 ° c . ( medium viscosity of 10 3 pa · s ) and presents an absorption peak at 1100 nm . a string made of this glass paste , with a diameter of 1 mm , was applied along the external perimeter of a dsc with 7 cm long and 5 cm wide . in the photoelectrode glass substrate was created a small incision for a better definition of the glass paste string . after sintering the titanium dioxide semiconductor deposited onto the photoelectrode glass plate , this was quickly heated from 450 ° c . up to 520 ° c ., at a rate of 10 ° c . per minute . the sealing glass precursor is immediately deposited along the entire incision made at the glass plate kept at 520 ° c . a constant temperature period , between 385 ° c . and 420 ° c ., should be achieved after the deposition . this cooling step is crucial to avoid an overheating of the counter - electrode when it contacts the photoelectrode glass substrate . the counter - electrode , also prepared with an incision along the soldering line , was then placed on top of the photoelectrode at a temperature of 385 ° c . a small aluminum frame guarantees a constant 30 μm distance between the photoelectrode and counter - electrode glass sheets . from the counter - electrode &# 39 ; s side , a 120 w medium power laser diode of 1064 nm wavelength strikes perpendicularly the sealing glass precursor . the laser beam passes through the dsc perimeter several times until all the gas bubbles formed during the glass fusing process disappear and , consequently , the correct soldering of the cell takes place . at the end of the procedure the cell is left to cool down to room temperature , while a nitrogen flow is used to remove potential contaminants introduced during the sealing process . this nitrogen flow was introduced in the cell through the holes previously made in the counter - electrode glass plate for the subsequent introduction of dye and electrolyte . fig1 presents , in a non limitative way , a scheme of an exemplary embodiment of a sealing method . in particular the referred figure shows : 1 . a transparent conducting sheet of glass ( tco ), the dsc photoelectrode substrate ; 2 . a transparent conducting sheet of glass ( tco ), the dsc counter - electrode substrate ; 4 . the sealant of the two electrodes ( material : glass precursor , a glass paste or a glass powder , of low or very low melting point ); fig2 presents a longitudinal cut of a sealed dsc , in addition to what was described in fig1 : 5 . the sealant of the hole made at the counter - electrode side for the injection of dye and electrolyte . ( material : glass precursor , a glass paste or a glass powder , of low and very low melting point ). the process of sealing the photoelectrode ( 1 ), containing the semiconductor ( 11 ), and the counter - electrode ( 2 ) occurs by means of a sealant ( 4 ) applied in the external perimeter of the glass sheet of the photoelectrode ( 1 ). the counter - electrode ( 2 ) is placed on the top of the photoelectrode ( 1 ) substrate . the sealing process occurs when the laser crosses the counter - electrode perpendicularly ( 2 ) causing the fusion of the sealant ( 4 ) placed between the electrodes ( 1 ) and ( 2 ). the sealing of the hole , created to inject the electrolyte and the dye into the cell , is made by depositing a small amount of glass sealant ( 5 ) in the hole area and then fusing this material ( 5 ) with a laser beam . the glass precursor with very low melting point can be the paste 8596 ( devitrifying solder glass ) or the powder glass 8465 ( vitreous solder glass ) from schott [ 31 ] . the glass precursor with low melting point can be the glass paste 8516 ( ir - absorbing sealing glass ), also from schott [ 31 ] . the laser used to perform the sealing process has a maximum power higher than 100 w in the wavelength range between 1000 nm and 1200 nm . in order to use the referred glass materials , the respective operational limitations , reported by the manufacturer , should be taken into account . this way , the photoelectrode has to be heated between 450 ° c . and 520 ° c . ; the counter - electrode has to be heated between 385 ° c . and 420 ° c . ; the glass precursor string has to be applied in the photoelectrode ; and the laser beam has to be applied from the counter - electrode glass substrate side . b . o &# 39 ; regan , m . grätzel ; “ a low - cost , high - efficiency solar - cell based on dye - sensitized colloidal tio 2 films ”; nature , 353 , pg . 737 , 1991 . a . kay , m . grätzel , b . o &# 39 ; regan ; “ process for producing a photoelectrochemical cell and a cell thus produced ”; wo9318532 , 1993 . s . s . hegedus , a . luque ; “ status , trends , challenges and the bright future of solar electricity from photovoltaics ” em handbook of photovoltaic science and engineering , editado por s . s . hegedus e a . luque , john wiley & amp ; sons , ltd , 2003 . k . hara , h . arakawa ; “ dye - sensitized solar cells ”, em handbook of photovoltaic science and engineering , editado por s . hegedus e a . luque , john wiley & amp ; sons , ltd , 2003 . m . grätzel , k . kalyanasundaram ; “ artificial photosynthesis : efficient dye - sensitized photoelectrochemical cells for direct conversion of visible light to electricity ”; current science , 66 ( 10 ), 706 - 714 , 1994 . f .- t . kong , s .- y . dai , and k .- j . wang ; “ review of recent progress in dye - sensitized solar cells ”; advances in optoelectronics , vol . 2007 , 13 pp ., 2007 . 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