Dye-sensitized solar cell and a method for manufacturing the solar cell

Abstract

The present invention relates to a dye-sensitized solar cell including a light absorbing layer (1), a first conducting layer (2) for extracting photo-generated electrons from the light absorbing layer, a counter electrode including a second conducting layer (3), a porous insulating layer (5b) disposed between the first and second conducting layers, and a conducting medium for transferring charges between the counter electrode and the working electrode. The solar cell further comprises a third conducting layer (6b) disposed between the porous insulating layer (5b) and the second conducting layer (3) and in electrical contact with the second conducting layer, and the third conducting layer includes a porous substrate (8) made of an insulating material and conducting particles accommodated in the pores of the porous substrate and forming a conducting network (9) through the insulating material.

Claims

1. A method for manufacturing a dye-sensitized solar cell comprising a first and a second conducting layer (2,3) and a porous insulating layer (5b) disposed between the first and second conducting layer, wherein the method comprises: depositing a blocking agent on a top side of a porous substrate (8) made of an insulating material, to form a blocking layer (10) in a portion (8b) of the substrate, infiltrating the porous substrate from a bottom side of the substrate with conducting particles having a size smaller than the pore size of the substrate to form a third conducting layer (6b) in another portion (8a) of the substrate, depositing a porous conductive layer on the top side of the porous substrate to form the first conducting layer, depositing a light absorbing layer comprising TiO.sub.2 on the first conducting layer, depositing an ink comprising conductive particles on the bottom side of the porous substrate to form the second conducting layer, and heat treating the substrate to burn off the blocking layer thus forming the porous insulating layer.

2. The method according to claim 1, wherein said portion (8b) of the porous substrate containing said blocking layer (10) is thinner than said another portion (8a) of the porous substrate.

3. The method according to claim 1, wherein the blocking layer comprises at least one of polymers, ceramic particles, glass fibers, polymer fibers, carbon nanotubes (CNT), nanocellulose, and micro fibrillated cellulose.

4. The method according to claim 1, wherein the depositing of the porous conductive layer is made by depositing an ink comprising conductive particles on the top side of the porous substrate to form the first conducting layer.

5. The method according to claim 1, wherein the light absorbing layer comprises perovskite.

6. The method according to claim 1, wherein the porous substrate comprises woven microfibers.

7. The method according to claim 1, wherein the thickness (t1) of the third conducting layer (6b) is less than 1 mm.

8. The method according to claim 1, wherein the thickness (t2) of the porous insulating layer (5b) is between 0.1 μm and 20 μm.

9. The method according to claim 1, wherein said conducting particles are made of the same material as is used in the second conducting layer (3).

10. The method according to claim 1, wherein said conducting particles are made from a material selected from the group consisting of titanium, titanium alloys, nickel, nickel alloys, carbon based materials, conducting oxides, conducting nitrides, conducting carbides, conducting silicides, and mixtures thereof.

11. The method according to claim 7, wherein the thickness (t1) of the third conducting layer (6b) is less than 100 μm.

12. The method according to claim 8, wherein the thickness (t2) of the porous insulating layer (5b) is between 0.5 μm and 10 μm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will now be explained more closely by the description of different embodiments of the invention and with reference to the appended figures.

(2) FIG. 1 shows a prior art dye-sensitized solar cell.

(3) FIG. 2 shows an example of a dye-sensitized solar cell according to the invention.

(4) FIG. 3 shows another example of a dye-sensitized solar cell according to the invention.

(5) FIG. 4 illustrates an example of a method for manufacturing a dye-sensitized solar cell according to the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

(6) FIG. 2 shows a first example of a dye-sensitized solar cell according to the invention. The dye-sensitized solar cell comprises a working electrode in the form of a light absorbing layer 1, a first conducting layer 2 for extracting photo-generated electrons from the light absorbing layer 1, a counter electrode including a second conducting layer 3, a porous insulating layer 5a arranged between the first and second conducting layers, and a conducting medium (not shown) for transferring charges between the counter electrode and the working electrode. The dye-sensitized solar cell further comprises a third conducting layer 6a disposed between the porous insulating layer 5a and the second conducting layer 3 and in electrical contact with the second conducting layer 3.

(7) The third conducting layer 6a includes a porous substrate 4 made of an insulating material and conducting particles 7 forming a conducting network through the porous substrate 4. The conducting particles are disposed in pores of the porous substrate 4. The porous insulating layer 5a is suitably formed by printing a layer of insulating material on a top side of the porous substrate 4. The insulating material is, for example, an inorganic material that is positioned between the first and third conducting layers and insulates the first and third conducting layers from each other and creates a porous insulating layer between the first and third conducting layer after heat treatment. The porous substrate 4 extends from the second conducting layer 3 to the porous insulating layer 5a. In this embodiment, the porous insulation layer 5a is a separate layer disposed on one side of the porous substrate 4. The first conducting layer 2 is, for example, formed by printing conducting particles on the porous insulating layer 5a. Suitably, all of the layers 1,2,3 and 5a are formed by printing. The porous insulating layer 5a is, for example, made of ceramic microfibers, or materials derived by delaminating layered crystals such 2D materials or nanosheets.

(8) FIG. 3 shows a second example of a dye-sensitized solar cell according to the invention. The dye-sensitized solar cell comprises a working electrode in the form of a light absorbing layer 1, a first conducting layer 2, a counter electrode including a second conducting layer 3, and porous substrate 8 made of an insulating material. The porous substrate 8 comprises a first portion 8a including conducting particles 9 forming a conducting network in the insulating material of the porous substrate, and a second portion 8b without any conducting particles and forming a porous insulating layer 5b. Thus, the first portion 8a forms a third conducting layer 6b, and the second portion 8b forms a porous insulating layer 5b. In this embodiment, the porous insulating layer 8b is formed as an integral part of the porous substrate 8.

(9) The conducting layers 2,3,6a,6b are porous to allow a conducting medium to penetrate through the conducting layers. Suitably, the conducting medium is a solid state hole conductor, or an ionic liquid based electrolyte or a cobalt complex based electrolyte.

(10) However, the conducting medium can be any suitable conducting medium. The conducting medium can be a liquid, a gel, or a solid material such as a semiconductor. Examples of electrolytes are liquid electrolytes (such as those based on the I-/I3-, redox couple or cobalt complexes as redox couple), gel electrolytes, dry polymer electrolytes and solid ceramic electrolytes. Examples of semiconductors are inorganic semiconductors, such as CuSCN or CuI, and organic semiconductors, such as, e.g., Spiro-OMeTAD.

(11) The porous substrate 4, 8 is, for example, made of microfibers. A microfiber is a fibre having a diameter less than 10 μm and length larger than 1 nm. Suitably, the porous substrate comprises woven microfibers. Ceramic microfibers are fibres made of a refractory and inert material, such as glass, SiO2, Al2O3 and aluminosilicate. Organic microfibers are fibres made of organic materials such as polymers such as, e.g., polycaprolactone, PET, PEO etc, or cellulose such as, e.g., nanocellulose (MFC) or wood pulp. The porous substrate 4, 8 may comprise woven microfibers and non-woven microfibers disposed on the woven microfibers. The thickness of the porous substrate 4, 8 is suitably between 10 μm and 1 mm. Such a layer provides the required mechanical strength.

(12) The porous substrate 4, 8 is infiltrated by conducting particles 7 so that a conducting network is formed through the insulating material and by that the third conducting layer 6a, 6b is achieved. The network of electrical particles in the third layer is in electrical contact with the second conducting layer 3. The porous insulating layer 5a, 5b prevents short circuit between the first and second conducting layers. The conducting particles must be smaller than the pore size of the substrate 4, 8 in order to be infiltrated effectively. The conducting particles form a conducting network 7,9 through the insulating material of the substrate. The conducting network 7,9 is in direct physical and electrical contact with the second conducting layer 3 of the counter electrode. The conducting particles serve the function of transferring electrons from the counter electrode to the conducting medium. The resistive losses in the conducting medium are reduced due to the conducting network in the substrate. Thus, it possible to use a thick porous substrate, and still achieve minimum electrical resistive losses in the conducting medium.

(13) Since the network of conducting particles is in direct physical and electrical contact with the counter electrode and in the same time are infiltrated a certain distance into the substrate, it is possible for the counter electrode to transfer electrons via the conducting particles to the conducting medium effectively closer to the light absorbing layer resulting in a smaller effective distance between the counter electrode and the light absorbing layer. Therefore the electrical losses in the conducting medium can be reduced by infiltrating conducting particles into the substrate. In the case of using a semiconductor with low electronic conductivity as a conducting medium, it is necessary to infiltrate the semiconductor through the light absorbing layer and through the current collecting layer and into the porous substrate deep enough such that the semiconductor is brought into direct physical and electrical contact with the infiltrated conducting particles.

(14) Preferably, the thickness t1 of the third conducting layer 6a, 6b is less than 1 mm, and most preferably less than 100 μm. In this example, the porous substrate 4 has been infiltrated with conducting particles from a bottom side. The conducting particles can also be catalytic. The conducting particles can be made of metal, metal alloy, metal oxide, or other conducting materials, for example, titanium, titanium alloys, nickel, nickel alloys, carbon based materials, conducting oxides, conducting nitrides, conducting carbides, conducting silicides, or mixtures thereof.

(15) Electrical contact between the first and second conducting layers is prevented by the porous insulating layer 5a,5b. For example, the thickness t2 of the porous insulating layer is between 0.1 μm and 20 μm, and preferably between 0.5 μm and 10 μm.

(16) The conducting layers 2,3,6a,6b are porous to allow the conducting medium to penetrate through the conducting layers. The material forming the conducting layer 2, 3 must have a suitable corrosion resistance as to withstand the environment in the solar cell, and preferably also be resistant to temperatures above 500° C. in air without losing adequate conductivity. Preferably, the conducting layers 2, 3 are made of a material selected from a group consisting of titanium, titanium alloys, nickel, nickel alloys, graphite, and amorphous carbon, or mixtures thereof. Most preferably, the conducting layers 2, 3 are made of titanium or a titanium alloy or mixtures thereof.

(17) Preferably, the thickness t) of the first conducting layer 2 is between 0.1 and 40 μm, or preferably between 0.3 and 20 μm.

(18) The light absorbing layer 1 of the working electrode may include a porous TiO2 electrode layer deposited onto the first conducting layer 2. The TiO2 electrode layer may comprise TiO2 particles dyed by adsorbing dye molecules on the surface of the TiO2 particles. Alternatively, the first conductive layer has a surface layer of TiO2 and the light absorbing layer is a perovskite layer. The porosity of the porous substrate will enable charge transport through the substrate.

(19) In the following, an example of a method for manufacturing the first example of a solar cell according to the invention is described.

(20) A porous substrate 4 made of an insulating material is infiltrated with conducting particles having a size smaller than the pore size of the substrate to form a third conducting layer. The substrate is infiltrated so that a network of conduction particles is formed through the entire substrate. A layer of insulating material is deposited on one side of the porous substrate to form a porous insulating layer. The insulating material is, for example, microfibers made of a ceramic or organic material. An ink comprising conductive particles are deposited on the porous insulating layer to form the first conducting layer, and an ink comprising conductive particles are deposited on an opposite side of the porous substrate to form the second conducting layer. The porous insulating layer is, for example, deposited on the porous substrate by screen printing, slot die coating, spraying, or wet laying. The porous first and second conducting layers are, for example, deposited on the porous substrate by screen printing or any other suitable printing technique.

(21) In the following an example of a method for manufacturing the second example of a solar cell according to the invention is described with reference to FIG. 4. FIG. 4 illustrates the deposition sequence in the manufacturing method.

(22) Step 1: A blocking agent is deposited on a top side of a substrate 8 made of an insulating material, to form a blocking layer 10 in a second portion 8b of the substrate 8. The blocking layer is deposited in order to physically prevent the conducting particles from being infiltrated all the way to other side of the substrate. Therefore, the blocking layer 10 prevents direct physical and electrical contact between the first conducting layer and the conducting particles. The blocking layer may consist of polymers, ceramic particles, polymer fibres, glass fibers, carbon nanotubes (CNT), nanocellulose or microfibrillated cellulose (MFC). It is advantageous to use fibers as a blocking agent in the blocking layer. It is advantageous to use fibers with very small diameter.

(23) Step 2: The porous substrate 8 is infiltrated from a bottom side of the substrate with conducting particles having a size smaller than the pore size of the substrate to form a third conducting layer 6b in a first portion 8a of the substrate. The conducting particles may consist of the same material as is used in the second conducting layer. It is also possible to use other types of particles such as carbon based materials (graphite, carbon black, CNT, graphene, etc). It is also possible to use other types of particles such as conducting oxides (ITO, FTO, ATO etc) or carbides, nitrides or silicides.

(24) Step 3: An ink comprising conductive particles is printed on the top side of the porous substrate 8 to form the first conducting layer 2.

(25) Step 4: An ink comprising conductive particles is printed on the bottom side of the porous substrate 4 to form the second conducting layer 3.

(26) Step 5: A TiO2 electrode layer is deposited onto the first conducting layer 2 to form the working electrode 1.

(27) Step 6: The substrate is heat treated to burn off the blocking layer 10 thus forming the porous insulating layer 5b.

(28) In the following two more detailed examples of methods for manufacturing a solar cell according to the invention will be described.

Example 1

(29) Liquid Redox Electrolyte Based Dye-Sensitized Solar Cell (DSC)

(30) In the first step a 28 μm thin glass fabric (MS1037, Asahi Kasei E-materials), was wet laid with a glass microfiber stock solution containing C-glass microfiber, fiber diameter: 0.5 μm) and water based colloidal silica.). The wet laid glass fabric was then dried at 110° C. 5 min in air in a belt oven.

(31) Subsequently in a second step the glass microfiber deposited glass fabric was then wet laid with a solution containing dispersed glass microfibers and nanocellulose on the other side in order to create a blocking layer: The nanocellulose which was added to the second glass fiber stock serves the function of creating a blocking layer that prevents conducting particles from passing through the blocking layer. The blocking effect can be enhanced by increasing the amount of added nanocellulose to the glass fiber stock. Thus, infiltrated particles in the third conducting layer can therefore be blocked by the blocking layer.

(32) A variation of the second step is to omit adding glass microfiber to the solution that contains nanocellulose and is used to create the blocking layer. Another variation of the second step is to print or spray a solution of nanocellulose onto one of the sides of the dried glass microfiber treated glass fabric in order to create a blocking layer. Another variation of the second step is to use dispersed carbon nanotubes or a dispersed 2D material instead of nanocellulose in order to create a blocking layer.

(33) Subsequently in a third step, an ink containing platinized FTO particles was prepared by first mixing FTO particles of 80 nm diameter with an isopropanol solution of hexachloroplatinic acid and then drying the mixture at 60 C for 30 min and then heating the treated powder in air to 400 C for 15 min. After the heat treatment the platinized FTO powder was grinded together with terpineol in a ball mill to create the final ink containing platinized FTO particles in terpineol. In the next step the double sided deposited glass fabric with a blocking layer was infiltrated with conducting catalytic particles by printing, for example, screen printing, the ink containing platinized FTO particles on the non-woven glass microfiber side opposite to the blocking layer side. The printed ink was then allowed to dry in air at 120 C for 10 min.

(34) A variation of the third step is to use other types of platinized conducting particles instead of FTO, such as, e.g., ATO, ITO, graphite, carbon black, graphene, or carbon nanotubes. Another variation of the third step is to use particles that are both conducting and catalytic such as metal carbides, metal nitrides and metal silicides.

(35) Subsequently in a fourth step an ink was prepared by mixing TiH2 with terpineol using 50:50 ratio by weight. The ink was then bead milled for 25 minutes at 5000 RPM using 0.3 mm zirconia beads. The zirconia beads were then separated from the ink by filtration. The filtered ink was then printed onto the double sided deposited glass fabric having a blocking layer and layer of infiltrated platinized FTO particles and then dried at 200° C. for 5 minutes. Subsequently the filtered ink was printed onto the other side of the glass fabric and then dried at 200° C. for 5 minutes. Subsequently the deposited glass fabric was vacuum sintered at 600° C. The pressure during sintering was lower than 0.0001 mbar. Consequently a first conducting layer and a second conducting layer and a third conducting layer was formed after the vacuum heating process.

(36) Subsequently in a fifth step a TiO2 based ink (Dyesol 18NR-T) was screen printed on top of the first conducting layer and then dried at 120 C for 10 min.

(37) Subsequently in a sixth step the treated glass fabric was heated in air to 500 C for 20 minutes. Consequently the deposited TiO2 layer was sintered and the nanocellulose based blocking layer was removed by combustion.

(38) Subsequently in a seventh step the treated glass fabric was immersed in a solution of 1 mM Z907 dye in methoxy-propanol and heat treated at 70° C. for 120 minutes and then rinsed in methoxy propanol and dried. Consequently the sintered TiO2 film was dye-sensitized.

(39) Subsequently in an eighth step an iodide/triiodide (I-/I3)-based redox electrolyte containing polymer was deposited on top of the TiO2 layer in the form of a gel.

(40) Subsequently in a ninth step the cell was sealed by infiltrating a polymer at the edges around the DSC and covering the both sides with glass in the same time allowing for external electrical connection to the first and second conducting layer.

Example 2

Solid State Hole Conductor Based DSC

(41) In the first step same materials and procedure as the first step in example 1 is used.

(42) Subsequently in a second step same materials and procedure as in the second step in example 1 is used.

(43) Subsequently in a third step an ink containing carbon particles was prepared by mixing 75 grams graphite and 25 grams carbon black (Super P-Li) and 15 grams of TiO2 (20 nm diameter) with terpineol then grinding the mixture in a ball mill to produce the final ink. In the next step the double sided deposited glass fabric with a blocking layer was infiltrated with conducting carbon particles by printing, for example screen printing, the ink on the non-woven glass microfiber side opposite to the blocking layer side. The printed ink was then allowed to dry in air at 120° C. for 10 min. A variation of the third step is to use carbon particles that are gold plated.

(44) Another variation of the third step is to use other types of particles that have both sufficient conductivity and also low ohmic resistance to the hole conductor such as FTO or ITO.

(45) Subsequently in a fourth step an ink was prepared by mixing TiH2 with terpineol using 50:50 ratio by weight. The ink was then bead milled for 25 minutes at 5000 RPM using 0.3 mm zirconia beads. The zirconia beads were then separated from the ink by filtration. The filtered ink was then printed onto the double sided deposited glass fabric having a blocking layer and layer of infiltrated carbon particles and then dried at 200° C. for 5 minutes. Subsequently the filtered ink was printed onto the other side of the glass fabric and then dried at 200° C. for 5 minutes. Subsequently the deposited glass fabric was vacuum sintered at 600° C. The pressure during sintering was lower than 0.0001 mbar. Consequently a first conducting layer and a second conducting layer and a third conducting layer was formed after the vacuum heating process.

(46) Subsequently in a fifth step a TiO2 based ink (Dyesol 18NR-T) was screen printed on top of the first conducting layer and then dried at 120 C for 10 min. The TiO2 based ink was diluted 5 times with terpineol before printing. A variation is to omit the fifth step and therefore to omit the deposition of the TiO2 based ink.

(47) Subsequently in a sixth step the treated glass fabric was heated in air to 500 C for 20 minutes. Consequently the deposited TiO2 layer was sintered and the nanocellulose blocking layer was removed by combustion.

(48) In the case the deposition of TiO2 was omitted in the fifth step there is no deposited TiO2 layer to be sintered and the nanocellulose will be removed by combustion.

(49) Subsequently in a seventh step a thin layer of a dimethylformamide solution of organic-inorganic perovskite (CH.sub.3NH.sub.3PbI.sub.3) was ultrasonically sprayed onto the TiO2 layer and dried at 125 C for 30 min.

(50) In the case the deposition of TiO2 was omitted in the fifth step the organic-inorganic perovskite is sprayed directly onto the first conducting layer after sintering of the first conducting layer.

(51) A variation of the seventh step is to use mixed halides such as (CH.sub.3NH.sub.3PbI.sub.3xCl.sub.x).

(52) Another variation of the seventh step is to use tin based perovskite such as CH.sub.3NH.sub.3SnI.sub.3

(53) Another variation of the seventh step is to deposit the solution of the perovskite by the ink jet method or by slot die coating.

(54) Another variation of the seventh step is to deposit the perovskite in a sequential two-step process by first depositing PbI2 solution and then drying and then depositing CH3NH3I solution and then drying and then heating the two dried deposits in order to complete the reaction between PbI2 and CH3NH3I to form CH3NH3PbI3.

(55) Another variation of the seventh step is to deposit the perovskite in a two-step process by first depositing SnI2 and then drying and then depositing CH3NH3I and then drying and then heating the two deposits in order to complete the reaction between SnI2 and CH3NH3I to form CH3NH3SnI3.

(56) Subsequently in an eighth step a solution of spiro-MeOTAD (84 mg spiro-OMeTAD in 1 ml chlorobenzene, mixed with 7 microliters of tert-butyl pyridine and 15 microliters of LiTFSI (lithium bis(trifle romethanesulfonyl)imide) in acetonitrile) was ultrasonically sprayed on top of the TiO2 layer and dried 5 min at 50 C.

(57) A variation of the eighth step is to deposit solutions of CuI, CuSCN or P3HT instead of spiro-OMeTAD as a hole conductor.

(58) Subsequently in a ninth step the cell was sealed by infiltrating a polymer at the edges around the DSC and covering both sides with glass and in the same time allowing for external electrical connection to the first and second conducting layer.

(59) The porous insulating layer 5a can be deposited on the porous substrate by any of screen printing, slot die coating, spraying, or wet laying.

(60) The invention is not limited to the above described embodiment and can be varied within the scope of the claims. For example, the method for manufacturing a dye-sensitized solar cell can be carried out in many different ways.