A DYE-SENSITIZED SOLAR CELL UNIT, A PHOTOVOLTAIC CHARGER INCLUDING THE DYE-SENSITIZED SOLAR CELL UNIT AND A METHOD FOR PRODUCING THE SOLAR CELL UNIT

Abstract

The present invention relates to a dye-sensitized solar cell unit (1) comprising:—a working electrode comprising a porous light-absorbing layer (10),—a porous first conductive layer (12) including conductive material for extracting photo-generated electrons In from the light-absorbing layer (10),—a porous insulating layer (105) made of an insulating material,—a counter electrode comprising a porous catalytic conductive layer (106) formed on the opposite side of the porous insulating layer (105), and—an ionic based electrolyte for transferring electrons from the counter electrode to the working electrode and arranged in pores of the porous first conductive layer (12), the porous catalytic conductive layer (106), and the porous insulating layer (105), wherein the first conductive layer (12) comprises an insulating oxide layer (109) formed on the surfaces of the conductive material, and the porous catalytic conductive layer (106) comprises conductive material (107′) and catalytic particles (107″) distributed in the conductive material for improving the transfer of electrons from the conductive material (107″) to the electrolyte.

Claims

1. A dye-sensitized solar cell unit (1″) comprising: a working electrode comprising a light-absorbing layer (10), a porous first conducting layer (12, 12′) for extracting photo-generated electrons from the light-absorbing layer (10), wherein the light-absorbing layer (10) is arranged on top of the first conducting layer (12, 12′), a porous insulating layer (105a, 105b, 105c) made of an insulating material, wherein the porous first conducting layer (12′) is arranged on top of the porous insulating layer (105a, 105b, 105c), a counter electrode comprising: i. a second conducting layer (16) including conducting material, and ii. a porous third conducting layer (106a, 106b, 106c) disposed between the porous insulating layer (105a, 105b,105c) and the second conducting layer (16), and in electrical contact with the second conducting layer (16), and a liquid electrolyte for transferring electrons from the counter electrode to the working electrode, wherein the second conducting layer (16) is essentially non-catalytic and the third conducting layer (106a, 106b, 106c) comprises catalytic particles (107, 107″) for improving the transfer of electrons to the liquid electrolyte.

2. The dye-sensitized solar cell unit according to claim 1, wherein said catalytic particles (107, 107″) comprises carbon.

3. The dye-sensitized solar cell unit according to claim 1, wherein said catalytic particles (107″) comprises platinized carbon particles.

4. The dye-sensitized solar cell unit according to claim 1, wherein the third conducting layer (106a, 106b, 106c) comprises a mixture of conducting particles (107′) and said catalytic particles (107″), and the conducting particles (107′) is in electrical contact with the second conducting layer (16).

5. The dye-sensitized solar cell unit according to claim 4, wherein said conducting particles (107′) of the third conducting layer (106c) are made of titanium.

6. The dye-sensitized solar cell unit according to claim 4, wherein said third conducting layer (105c) comprises a mixture of titanium particles and platinized carbon particles.

7. The dye-sensitized solar cell unit according to claim 4, wherein said mixture comprises at least 10% by weight of catalytic particles (107″), and preferably at least 20% by weight of catalytic particles (107″).

8. The dye-sensitized solar cell unit according to claim 1, wherein the catalytic particles (107″) are substantially evenly distributed in the third conducting layer (106c).

9. The dye-sensitized solar cell unit according to claim 1, wherein at least 80% of said catalytic particles have a diameter less than 50 nm.

10. The dye-sensitized solar cell unit according to claim 1, wherein the first conducting layer (12) comprises porous titanium, and a titanium oxide layer (109) is formed on the surfaces of the porous titanium.

11. The dye-sensitized solar cell unit according to claim 10, wherein the thickness of said titanium oxide layer (109) is larger than 5 nm, preferably larger than 10 nm, and more preferably larger than 20 nm.

12. The dye-sensitized solar cell unit according to claim 10, wherein the thickness of said titanium oxide layer (109) is between 10 and 200 nm, and preferably between 20-50 nm.

13. The dye-sensitized solar cell unit according to claim 1, wherein the thickness of the third conducting layer (106c) is at least 1 μm, preferably at least 5 μm and most preferably at least 10 μm.

14. The dye-sensitized solar cell unit according to claim 1, wherein the electrolyte is any of a liquid iodide/triiodide electrolyte, a liquid copper complex, or a liquid cobalt complex based electrolyte, or a combination thereof.

15. The dye-sensitized solar cell unit according to claim 1, wherein the solar cell unit (2) produces at least 5 μW/cm.sup.2 when the light intensity received by the light-absorbing layer is 200 Lux, and at least 600 μW/cm.sup.2 when the light intensity received by the light-absorbing layer is 20 000 Lux.

16. The dye-sensitized solar cell unit according to claim 1, wherein the solar cell unit (2) produces at least 150 μW/cm.sup.2 when the light intensity received by the light-absorbing layer is 5 000 Lux.

17. The dye-sensitized solar cell unit according to claim 1, wherein the solar cell unit (2) generates a voltage varying less than 40% when the light intensity received by the light-absorbing layer is varying between 200 and 50 000 Lux.

18. The dye-sensitized solar cell unit according to claim 1, wherein the solar cell unit (2) produces a current of at least 15 μA/cm.sup.2 when the light intensity received by the light-absorbing layer is 200 Lux, and the current produced by the solar cell unit is linearly increasing when the light intensity received by the light-absorbing layer increases from 200 to 20 000 Lux.

19. A photovoltaic charger specially adapted for charging an electronic device, comprising: a dye-sensitized solar cell unit (1″) according to claim 1, an encapsulation (5) encapsulating the solar cell unit, a first conductor (18) electrically connected to the first conducting layer (12), and at least one second conductor (20) electrically connected to the second conducting layer (16), wherein the photovoltaic charger contains only one single solar cell unit (1″) and a boost converter (22) electrically connected to the first and second conductors (12, 16), and the boost converter is adapted to step up the voltage from the solar cell unit while stepping down the current from the solar cell unit.

20. The photovoltaic charger according to claim 19, wherein the boost converter (22) is configured to convert the voltage from the solar cell unit (2) to a voltage that lies between 1 and 10 V.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0118] FIG. 1 shows a first example of a dye-sensitized solar cell unit.

[0119] FIG. 2 shows a second example of a dye-sensitized solar cell unit.

[0120] FIG. 3 shows a view from above on a photovoltaic charger in accordance with one or more embodiments of the invention.

[0121] FIG. 4 shows a cross section through the photovoltaic charger shown in FIG. 3 in an enlarged view.

[0122] FIG. 5 shows a diagram of measured values for generated voltage (mV) for light intensities between 200 and 20 000 Lux for the third example of a solar cell unit having an electrolyte comprising iodide and triiodide ions.

[0123] FIG. 6 shows a diagram based on measured values for generated current (μA/cm.sup.2) for light intensities between 200 and 20 000 Lux for the third example of the solar cell unit.

[0124] FIG. 7 shows a diagram based on measured values for generated power per area (μW/cm.sup.2) for light intensities between 200 and 20 000 Lux for the third example of the solar cell unit having an electrolyte comprising iodide and triiodide ions.

[0125] FIG. 8 shows a diagram of measured values for generated voltage (mV) for light intensities between 200 and 50 000 Lux for a third example of a solar cell unit having an electrolyte comprising copper ions.

[0126] FIG. 9 shows a diagram based on measured values for generated current (μA/cm.sup.2) for light intensities between 200 and 50 000 Lux for the third example of the solar cell unit having an electrolyte comprising copper ions.

[0127] FIG. 10 shows a diagram based on measured values for generated power per area (μW/cm.sup.2) for light intensities between 200 and 50 000 Lux for the third example of solar cell unit having an electrolyte comprising copper ions.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

[0128] Aspects of the present disclosure will be described more fully hereinafter with reference to the accompanying drawings. The dye-sensitized solar cell unit and the photovoltaic charger disclosed herein can, however, be realized in many different forms and should not be construed as being limited to the aspects set forth herein. Like numbers in the drawings refer to like elements throughout.

[0129] The terminology used herein is for the purpose of describing particular aspects of the disclosure only and is not intended to limit the invention.

[0130] Unless otherwise defined, all terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs.

[0131] FIG. 1 shows an example of a dye-sensitized solar cell unit 1. The solar cell unit 1 comprises a working electrode comprising a light-absorbing layer 10 and a porous first conductive layer 12 for extracting photo-generated electrons from the light-absorbing layer 10. Preferably, the light-absorbing layer 10 is porous. The light-absorbing layer 10 is arranged on top of the first conductive layer 12. The solar cell unit 1 further comprises a porous insulating layer 105 made of an insulating material, wherein the first conductive layer 12 is arranged on top of the porous insulating layer 105. For example, the porous insulating layer 105 is a porous substrate.

[0132] The solar cell unit 1 has a counter electrode comprising a porous catalytic conductive layer 106 comprising porous conductive material 107′ and catalytic particles 107″ distributed in the porous conductive material 107′ for improving the transfer of electrons to an electrolyte 110 disposed in pores of the porous catalytic conductive layer 106. In one aspect, the conductive material 107′ of the porous catalytic conductive layer 106 comprises conductive particles 107′. For example, the porous catalytic conductive layer 106 comprises a mixture of conductive particles 107′ and catalytic particles 107″, as shown in the enlarged figure to the right in FIG. 1. Preferably, the catalytic particles 107″are substantially evenly distributed in the conductive material 107′ of the catalytic conductive layer 106.

[0133] The porous catalytic conductive layer 106 is arranged adjacent to the porous insulating layer 105 on an opposite side of the insulating layer compared to the first conductive layer.

[0134] In one aspect, the counter electrode of the solar cell unit 1 comprises a second conductive layer 16 including a conductive material. The porous catalytic conductive layer 106 is disposed between the porous insulating layer 105 and the second conductive layer 16. The catalytic conductive layer 106 is in electrical contact with the second conductive layer 16. The second conductive layer 16 is essentially non-catalytic. The first conductive layer 12, the catalytic conductive layer 106, and the insulating layer 105 are porous to allow the electrolyte to penetrate through the layers to reach the light-absorbing layer 10. In one aspect, the second conductive layer is also porous. In an alternative embodiment, the second conductive layer 16 can be omitted.

[0135] The solar cell unit 1 also comprises an ionic based electrolyte 110 for transferring charges between the counter electrode and the working electrode. For example, the ionic based electrolyte is a liquid or a gel. The ionic based electrolyte is located in pores of the porous layers, such as the porous first conductive layer 12, the catalytic conductive layer 106, the porous insulating layer 105, and the light-absorbing layer 10. The ionic based electrolyte may also be located in pores of the second conductive layer 16, if the second conductive layer is porous.

[0136] The conductive material in the porous catalytic conductive layer 106 is a part of the counter electrode. Consequently, since the catalytic conductive layer 106 and second conductive layer 16 are in electrical contact, the effective distance between the light-absorbing layer 10 and the second conductive layer 16 is shorter and the resistive losses in the conductive medium are therefore reduced. Further, the catalytic particles 107″ facilitating the transfer of electrons from the conductive material 107′ in the porous catalytic conductive layer to the electrolyte 110.

[0137] In one aspect, the catalytic conductive layer 106 comprises a mixture of conductive particles 107′ and catalytic particles 107″. The conductive particles are in electrical contact with the second conductive layer 16. Preferably, the conductive particles are non-catalytic and exclude catalytic material. The mixture of conductive particles and catalytic particles will result in efficient transfer of electrons from the catalytic conductive layer to the electrolyte.

[0138] The conductive particles of the catalytic conductive layer include conductive material and are in electrical contact with the second conductive layer 16. The catalytic particles are distributed among the conductive particles. The conductive particles act as a holder for the catalytic particles and keep them in place. The conductive particles may form a matrix for housing the catalytic particles and keeping them in place. For example, the matrix comprises sintered metal particles.

[0139] In one aspect, the catalytic particles are substantially evenly distributed among the conductive particles. By distributing the catalytic particles substantially evenly in the catalytic conductive layer, transfer of electrons from the conductive particles to the electrolyte is improved. In one aspect, the conductive particles are attached to each other, for example, by sintering. The conductive particle may form a matrix housing the catalytic particles. The catalytic particles are embedded in the matrix of conductive particles. For example, the catalytic conductive layer comprises sintered conductive particles, and catalytic particles are disposed between the conductive particles. The conductive particles act as a glue between catalytic particles and keep the catalytic particles in position between the conductive particles.

[0140] In one aspect, at least 80% of the catalytic particles 107″ have a diameter less than 50 nm. Such small particles have a large surface/volume ratio and will provide an efficient catalyzation with a reduced volume of catalytic material. If the catalytic material is platina, this will reduce the cost for the catalytic material. In one aspect, at least 80% of the conductive particles have a diameter larger than 100 nm. Preferably, the size of conductive particles is between 0.1-15 μm.

[0141] The conductive material of the first and second conductive layers 12, 16 can, for example, be metal, metal alloy, metal oxide, or other conductive materials, for example, titanium, titanium alloys, nickel, or nickel alloys. Suitably, the first and second conductive layers 12, 16 comprise titanium or an alloy thereof. For example, the conductive material of the first and second conductive layers is titanium. For example, the first conductive layer 12 may comprise sintered titanium particles in order to be porous. It is advantageous to use titanium since it is highly corrosion resistant, and ionic based electrolytes often are very corrosive.

[0142] The conductive material 107′ in the catalytic conductive layer 106 can, for example, be made of metal, metal alloy, metal oxide, or other conductive materials, for example, titanium, titanium alloys, nickel, or nickel alloys, indium or indium oxide. The catalytic particles 107″ are, for example, made of carbon-based materials such as graphene or graphite or carbon black or carbon nanotubes, platina or a combination thereof.

[0143] In one aspect, the catalytic particles 107″ comprise carbon particles. Carbon is inexpensive and environmentally friendly. More preferably, the catalytic particles 107″ include platinized carbon particles. Platina is a better catalyst than carbon, but it is expensive. By using a combination of platina and carbon, a good catalyst is achieved at a lower cost. The catalytic particles can be electrically conductive as well as catalytic. For example, carbon is electrically conductive as well as catalytic. However, carbon is a poor conductor in comparison to other conductive material, such as titanium.

[0144] The electrical conductivity of the first and second conductive layer 12, 16 can be higher than the electrical conductivity of the catalytic conductive layer 106. The combination of a catalytic conductive layer 106 with a mixture of conductive material and catalytic particles, and a second conductive layer 16 essentially without catalytic particles, will result in efficient transfer of electrons from the conductive particles 107′ of the counter electrode to the electrolyte as well as high electrical conductivity of the counter electrode.

[0145] Preferably, the catalytic conductive layer comprises between 1-50% by weight of catalytic particles. The % by weight of catalytic particles needed to achieve an efficient transfer of electrons from the conductive material to the electrolyte depends on the size and shape of the catalytic particles and the type of material in the catalytic particles and the type of conductive material. For example, the catalytic conductive layer may comprise between 5-30% by weight of catalytic particles. This range is, for example, suitable when the conductive particles consist of titanium and the catalytic particles consist of platinized carbon. However, as mentioned before, the % by weight of catalytic particles depends on the size of the particles.

[0146] For example, if the conductive material 107′ in the catalytic conductive layer 106 is titanium, the catalytic particles 107″ comprise platinized carbon, and the size of the catalytic particles 107″ is less than the size of the conductive particles 107′, the catalytic conductive layer 106 may comprise between 5-30% by weight of catalytic particles 107″ to provide an efficient transfer of electrons to the electrolyte. For example, the catalytic conductive layer comprises between 50 and 90% by weight of titanium, at least 5% by weight of carbon, and at least 0.001% by weight of platina. Titanium has good mechanical strength and keeps the platinized carbon particles in their positions in the catalytic conductive layer. Thus, carbon, platina and titanium together provide a catalytic conducting layer with high mechanical strength and a high ability to transfer electrons to the electrolyte.

[0147] In one aspect, the thickness t1 of the catalytic conductive layer 106 is at least 1 μm, preferably at least 5 μm and most preferably at least 10 μm. In one aspect, the thickness t1 of the catalytic conductive layer 106 is less than 100 μm, and preferably less than 20 μm. In one aspect, the thickness t2 of the porous insulating layer 105 is between 0.1 μm and 20 μm, and preferably between 0.5 μm and 10 μm. In one aspect, the thickness t4 of the second conductive layer 16 is at least 1 μm, preferably at least 10 μm and preferably at least 20 μm.

[0148] The first conductive layer 12 comprises an insulating oxide layer 109 formed on the surface of the conductive material, as shown in the enlarged figure to the left in FIG. 1. This oxide layer 109 is, for example, formed by oxidizing the conductive material of the first conductive layer.

[0149] The conductive material suitably comprises a metal or a metal alloy, for example, titanium. The surface of the conductive material is oxidized when it is exposed to air. The oxide layer 109 can be formed by performing a heat treatment of the first conductive layer in an oxidizing environment so that the conductive material becomes oxidized. The insulating oxide layer 109 provides an electrically insulating layer on the conductive material, which at least partly prevents transfer of electrons between the first conductive layer 12 and the electrolyte disposed in the pores of the first conductive layer 12.

[0150] In one aspect, the first conductive layer 12 comprises porous titanium, and a titanium oxide layer 109 formed on the surfaces of the porous titanium so that the oxide layer 109 electrically insulates the porous titanium of the first conductive layer and by that prevents electrons from leaking from the porous titanium in the first conductive layer to the electrolyte in the pores of the first conductive layer. Thus, the efficiency of the solar cell unit is increased. For example, the first conductive layer 12 comprises sintered titanium particles 107, and the surfaces of the sintered titanium particles 107 are covered by the titanium oxide layer 109, as shown in the enlarged figure to the left in FIG. 1. In one aspect, the thickness of the titanium oxide layer is larger than 5 nm, preferably larger than 10 nm, and more preferably larger than 20 nm. In one aspect, the thickness of the titanium oxide layer is between 10 and 200 nm, and preferably between 20-50 nm.

[0151] In particular, the combination of the insulating oxide layer 109 that prevents electrons from leaking from the first conductive layer to the liquid based electrolyte, and a counter electrode comprising a catalytic conductive layer 106 including catalytic particles 107″ distributed in a porous conductive material 107, and a non-catalytic conductive layer 16 that improves the efficiency of the counter electrode, will result in an efficient solar cell unit which is capable of producing power in a wide range of different light conditions. The solar cell unit works during poor as well as excellent lighting conditions, for example, indoors in artificial light, and outdoors in the shadow and when exposed to strong sunlight.

[0152] In one aspect, the electrolyte is any of a iodide/triiodide electrolyte, a copper complex-based electrolyte, or a cobalt complex-based electrolyte, or a combination thereof. In one aspect, the electrolyte comprises iodide (I.sup.−) and triiodide (I.sub.3.sup.−) and the content of triiodide in the conductive medium is between 1 mM and 20 mM. This embodiment makes it possible to achieve high power generation at low light intensities.

[0153] The insulating material of the porous insulating layer 105, is, for example, an inorganic material that is positioned between the first conductive layer 12 and the catalytic conductive layer 106, and insulates the first conductive layer 12 and the catalytic conductive layer 106 from each other. The porous insulating layer 105 is, for example, made of glass fibers, ceramic microfibers, or materials derived by delaminating layered crystals such 2D materials or nanosheets.

[0154] The solar cell unit 1 may comprise a porous substrate. The porous insulating layer 105 may comprise the whole substrate, as shown in FIG. 1, or only a part 114a of the porous substrate 114 as shown in FIG. 2. According to one aspect, the porous substrate is a sheet comprising woven microfibers extending through the entire solar cell unit. For example, the woven microfibers are made of glass fibers.

[0155] FIG. 2 shows an example of a dye-sensitized solar cell 1′ comprising a porous substrate 114 made of an insulating material. Like or corresponding parts in the FIGS. 1 and 2 are indicated with like numerals. The difference between the solar cells 1′ and 1 is that the porous catalytic conductive layer 106′ comprises a first part 114a of a porous substrate 114, and the porous insulating layer 105 comprises a second part 114b of the porous substrate 114. The catalytic conductive layer 106′ comprises conductive particles 107′ and catalytic particles 107″ disposed in pores of the first part 114a of the porous substrate 114. The conductive particles 107′ of the catalytic conductive layer 106′ form a conductive network 209 through the insulating material of the part 114a of the porous substrate 114. The conductive network 209 form one or more electrically conductive paths through the insulating material of the first part 114a of porous substrate. The conductive particles 107′ and the catalytic particles 107″ are disposed in pores of the porous substrate 114. Preferably, the size of the particles is less than the size of the pores in the porous substrate to be able to be infiltrated into the substrate during production of the solar cell. The conductive network 209 provides an extension of the second conductive layer, which extends into the porous substrate 114. Due to the conductive network in the porous substrate, the distance between the counter electrode and the light-absorbing layer does no longer depend on the thickness of the porous substrate. Thus, the thickness of the insulating layer can be reduced, and by that the distance between the counter electrode and the light-absorbing layer can be reduced. Accordingly, the resistive losses in the electrolyte are reduced.

[0156] In the following an example of a method for manufacturing the solar cell unit 1 is briefly described. [0157] 1) Preparing a first ink comprising conductive particles made of an electrically conductive material. The conductive particles are, for example, made of titanium hydride. [0158] 2) Preparing a second ink comprising a mixture of conductive particles and catalytic particles. The conductive particles are, for example, made of titanium hydride (TiH.sub.2) and the catalytic particles are, for example, platinized carbon particles. [0159] 3) Providing a porous insulating substrate, for example, a glass fabric. [0160] 4) Depositing conductive particles on one side of the porous insulating substrate, for example, by printing the first ink including the titanium hydride particles on one side of the porous insulating substrate. [0161] 5) The printed first ink is then allowed to dry in air, [0162] 6) Depositing a mixture of catalytic particles and conductive particles on the other side of the porous insulating substrate, for example, by printing the second ink including the titanium hydride particles and platinized carbon particles on the other side of the porous insulating substrate. [0163] 7) The printed second ink is then allowed to dry in air, [0164] 8) Depositing conductive particles on top pf the catalytic conductive layer, for example, by printing the first ink including the titanium hydride particles on the layer of mixture of catalytic particles and conductive particles. [0165] 9) The printed first ink is then allowed to dry in air, [0166] 10) The porous insulating substrate with the printed layers is then vacuum sintered, for example, at 600° C. for an hour. During the sintering process, the titanium hydride is transformed into titanium. Consequently, a first conductive layer including sintered titanium, a second conductive layer including sintered titanium, and a catalytic conductive layer including sintered titanium and platinized carbon particles disposed in pores between the sintered titanium are formed during the sintering process. [0167] 11) The porous insulating substrate with the sintered conductive layers is heated in air to form titanium oxide on the surfaces of the sintered titanium of the first conductive layer. [0168] 12) A TiO.sub.2 based ink is printed on top of the first conductive layer and then dried. The glass fabric with the layers is heated, for example, to 600° C. Consequently, the deposited TiO2 layer is sintered. [0169] 13) The sintered TiO2 layer is dye-sensitized to form a light-absorbing layer, [0170] 14) An ionic electrolyte, for example, an iodide/triiodide (I-/I3)-based redox electrolyte, is infiltrated in the porous layers. [0171] 15) The solar cell is sealed, for example, by a transparent encapsulation.

[0172] Alternatively, step 11 can be done simultaneously as sintering the TiO2 layer in step 12.

[0173] The porous conductive layers can be deposited on the porous substrate by any of screen printing, slot die coating, spraying, or wet laying.

[0174] During the heat treatment of step 11, titanium oxide is also formed on the catalytic conductive layer. It could be assumed that the oxide layer on the catalytic conductive layer would prevent the electrons from being transferred between the conductive material and the electrolyte disposed in the pores of the catalytic conductive layer. Surprisingly, it has been discovered that the catalytic particles, for example, platinized carbon particles, enable transfer of electrons from the conductive material to the electrolyte despite the oxide layer on the conductive material of the catalytic conductive layer.

[0175] FIG. 3 shows a view from above of an example of a photovoltaic charger 200. The photovoltaic charger 200 is specially adapted for powering portable electronic devices that can be used indoors as well as outdoors, such as earphones, laptops, tablets, mobile phones, and remote-control units. The photovoltaic charger 200 can also be used for powering small electronic devices embedded in other physical devices, such as vehicles, and home appliances, called Internet of Things (IoT).

[0176] The photovoltaic charger 200 comprises a solar cell unit 1, an encapsulation 5 enclosing the solar cell unit 1, a first conductor 18, and a second conductor 20. The photovoltaic charger may further comprise connection elements (not shown) for connecting the photovoltaic charger 200 to the electronic device. The solar cell unit 200 is a monolithic type DSC. The monolithic type of DSC differs from the standard DSC in that it is created on a single substrate, with multiple layer disposed on the substrate.

[0177] The encapsulation comprises a plurality of penetrations in connection to the first and second conductors for connecting the photovoltaic device to the external device. In other words, there are penetrations in the encapsulation for accessing the power produced by the photovoltaic device. Some kind of wiring will be going through the penetrations. For example, the first and second conductors may extend out of the encapsulation through the penetrations to connect to wiring for powering the external device. Alternatively, wires from the outside of the encapsulation are going through the penetrations and electrically connect to the first and second conductors. The penetrations are tightly fit around the wiring passing through the encapsulation such that no gas or liquid can pass through penetrations. For example, the penetrations are openings in the encapsulation tightly fit around wiring passing through the encapsulation.

[0178] The encapsulation 5 comprises a plurality of penetrations 7a-b arranged in connection to the first conductor 18 and the second conductor 20 for connecting the photovoltaic device 1 to the external device and by that accessing the power produced by the photovoltaic device. For example, the penetrations are lead trough openings in the encapsulation. Some kind of wiring will be going through the openings. For example, the first and second conductors 18, 20 may extend out of the encapsulation through the penetrations 7a-b to connect to wiring for powering the external device, as shown in FIG. 3. Alternatively, wires from the outside of the encapsulation are going through the penetrations and are electrically connected to the first and second conductors. The penetrations are tightly fit around the wiring such that no gas or liquid can pass through them. The penetrations can be made by having the wires or conductors that should go through the holes in place when the encapsulation is arranged on the solar cell unit 1. The encapsulation consists of top sheet 5a and bottom sheet 5b, which are, for example, adhesive films that are put together over the solar cell unit 1. Alternatively, the top and bottom sheets are made of a flexible plastic material, and the edges of the top and bottom sheets are bonded to each other by melting the plastic material. If the wires/conductors are already in place between sheets before the bonding and protrude at the edges of the sheets, the penetrations will be created during the bonding. Alternatively, the penetrations comprise through holes in the encapsulation made after encapsulation of the solar cell unit. The through holes are sealed after the wires/conductors have been arranged in the through holes. The locations of the penetrations will depend on the position of the first and second conductors. The number of penetrations can vary. There is at least one penetration for each of the first and second conductor. However, it is also possible to have a plurality of penetrations for each of the first and second conductors.

[0179] FIG. 4 shows an enlargement of a cross section through a part of the photovoltaic charger 200 shown in FIG. 3. The photovoltaic charger 200 comprises one solar cell unit 1, or solar cell unit 1′, which is described in more details with reference to FIGS. 1 and 2. For example, the light-absorbing layer 10 comprises dyed TiO.sub.2. Conventional dyes known in the art can be used. A dye is chosen to give good efficiency of the solar cell, especially in combination with a copper-based conductive medium. The light-absorbing layer 10 is arranged on top of the first conductive layer 12. The porous light-absorbing layer 10 is a porous TiO.sub.2 layer deposited onto the first conductive layer 12. The TiO.sub.2 layer comprises TiO.sub.2 particles dyed by absorbing dye molecules on the surface of the TiO.sub.2 particles. The light-absorbing layer 10 is positioned on a top side of the solar cell unit 1. The top side should be facing the light to allow the light to hit the dye molecules of the working electrode.

[0180] The first conductive layer 12 is in direct electrical contact with the light-absorbing layer 10. In this example, the second conductive layer 16 is porous. However, in an alternative embodiment, the second conductive layer 16 does not have to be porous. For example, the second conductive layer can be made of a metal foil. In this example, the porous insulating layer 105 comprises at least a part of a porous substrate. The porous substrate provides electrical insulation between the first conductive layer 12 and the catalytic conductive layer 106. The first conductive layer 12 and the catalytic conductive layer 106 are separated physically and electrically by the porous substrate. The porosity of the porous substrate will enable ionic transport through the insulating layer 105. The porosity of the first conductive layer 12 and the catalytic conductive layer 106 will enable ionic transport between the counter electrode and the working electrode.

[0181] The photovoltaic charger 200 contains only one single solar cell unit 1. At least the first conductive layer 12 and the porous substrate are continuously extending through the entire solar cell unit. The light-absorbing layer 10 and the second conductive layer 16 extend continuously at least through a main part of solar cell unit.

[0182] The solar cell unit 1 is filled with an electrolyte for transferring charges between the counter electrode and the light-absorbing layer 10. The electrolyte is, for example, a conventional I.sup.−/I.sup.−3 electrolyte or a similar electrolyte, or a copper (Cu) based electrolyte, or cobalt (Co) complex based electrolyte. The electrolyte comprises ions, for example, iodide ions (I.sup.−) and triiodide ions (I.sub.3.sup.−) or copper ions (Cu.sup.3+ and Cu.sup.+). Sunlight is harvested by the dye, producing photo-excited electrons that are injected into the conduction band of the TiO.sub.2 particles and further collected by the first conductive layer. At the same time, ions in the electrolyte transport the electrons from the second conductive layer to the light-absorbing layer 10. The first conductor 18 collects the electrons from the first conductive layer and the second conductor provides electrons to the second conductive layer such that the solar cell unit can continuously produce power from the incoming photons.

[0183] The electrolyte penetrates the pores of the light-absorbing layer 10, the first conductive layer 12, the porous insulating layer 105, the second conductive layer 16 and the catalytic conductive layer 106 to allow the ions to be transferred between the light-absorbing layer 10 and the second conductive layer 16 and by that transfer electrons from the working electrode to the light-absorbing layer.

[0184] There are many dyes that may be used and according to some aspects, the dye comprises triarylamine organic dye comprising any of, or a mixture of, dyes in the class Donor-π bridge-Acceptor (D-π-A) and in the class Donor-Acceptor-π bridge-Acceptor (D-A-π-A). Such dyes give good efficiency of the solar cell, especially in combination with a copper-based conductive medium. Of the first class photosensitizer are, for example, substituted (diphenylaminophenyl)-thiophene-2-cyanoacrylic acids or substituted (diphenylaminophenyl)cyclopenta-dithiophene-2-cyanoacrylic acids. Of the second class are, for example, substituted (((diphenylaminophenyl)benzothia-diazolyl)-cyclopentadithiophenyl)aryl/heteroaryl-2-cyanoacrylic acids or (((diphenyl-aminophenyl)-cyclopentadithiophenyl)benzothiadiazolyl)aryl/heteroaryl-2-cyano-acrylic acids.

[0185] The first conductor 18 is electrically connected to the first conductive layer 12, and the second conductor 20 is electrically connected to the second conductive layer 16. For example, the first and second conductors are made of metal to achieve high electrical conductivity.

[0186] The encapsulation 5 comprises a top sheet 5a covering a top side of the solar cell unit 1, and a bottom sheet 5b covering a bottom side of the solar cell unit. The encapsulation 5 encloses the solar cell unit and the electrolyte and acts as liquid barrier for the electrolyte and prevents the electrolyte from leaking from the photovoltaic charger 200. The top sheet 5a is transparent, or at least the part covering the active area of the solar cell unit 1 is transparent. The top sheet 5a on the top side of the solar cell unit covers the light-absorbing layer 10 and allows light to pass through. The top and bottom sheets 5a-b are, for example, made of a polymer material. A polymer material is robust and impact resistant, and flexible. The top and bottom sheets 5a-b are sealed at the edges in order to protect the solar cell unit against the surrounding atmosphere, and to prevent the evaporation or leakage of the electrolyte from the inside of the solar cell unit.

[0187] In one example, the porous substrate is a sheet comprising a fabric of woven microfibers. A microfiber is a fibre having a diameter less than 10 μm and larger than 1 nm. A fabric of woven microfibers can be made very thin and mechanically very strong. The fabric of woven microfibers contains holes between the woven yarns. The porous substrate may further comprise one or more layers of non-woven microfibers disposed on the woven microfibers to at least partly block the holes between the yarns. Further, the non-woven layer provides a smooth surface on the substrate, suitable for applying a smooth conductive layer on the substrate by printing. The substrate is, for example, made of glass, silica (SiO.sub.2), alumina (Al.sub.2O.sub.3), aluminosilicate or quartz. Suitably, the non-woven and woven microfibers of the porous substrate are made of glass fibres, which provides a robust and flexible substrate. The thickness of the fabric of woven microfibers is suitably between 4 μm and 30 μm, preferably between 4 μm and 20 μm to provide the required mechanical strength at the same time as it is thin enough to enable a fast transport of ions between the counter electrode and working electrode.

[0188] In one aspect, light-absorbing layer 10, and the first conductive layer 12 are non-transparent. In this example, the upper surface of the solar cell unit 1 is homogeneously black, as shown in FIG. 3. The TiO.sub.2 of the light-absorbing layer is black. There are no conductors extending across the surface of the solar cell unit 1 as it is in the prior art solar cell panels. This is because the photovoltaic charger 200 only contains one single solar cell unit, and not a plurality of series connected solar cell units, as in the solar panels used in the prior art photovoltaic chargers.

[0189] The size of the solar cell unit, i.e. the length and width of the solar cell unit, may vary depending on which device it is adapted to charge. Accordingly, the active area of the solar cell unit may vary depending on the need of power for the device to charge. There is no limit to the possible shape and size of the solar cell unit. For example, the size of the solar cell unit may vary between 1×1 cm with an active area of 1 cm.sup.2 and 1×1 m with an active area of 1 m.sup.2. There is no upper limit to the length and width of the solar cell unit. However, a solar cell unit larger than 1×1 m can be bulky to handle during manufacturing of the solar cell unit.

[0190] The photovoltaic charger 200 includes a single solar cell unit 1 and a boost converter 22 electrically connected to the first and second conductors 18, 20. A boost converter, also called step-up converter or step-up regulator, is a DC-to-DC power converter that steps up voltage while stepping down current from its input to its output. The voltage produced by the single solar cell unit is too low to charge certain types or batteries, for example, lithium batteries that require at least 3.6 V. The boost converter is adapted to step up the voltage from the solar cell unit 1 while stepping down the current from the solar cell unit. The required voltage level is achieved by connecting a boost converter to the single solar cell unit. Thus, it is possible to provide a photovoltaic charger having only one single solar cell unit capable to charge batteries that require different voltage levels.

[0191] The photovoltaic charger 200 comprises connection elements 3, 4 for connecting the photovoltaic charger to a battery of the electronic device, which it is charging. The boost converter 22 comprises input terminals electrically connected to the first and second conductors 18, 20 and output terminals electrically connected to the connection elements 3, 4.

[0192] The level of the generated voltage depends on the ions in the electrolyte. For example, if the electrolyte contains copper ions, the solar cell unit generates a voltage of about 1 V in an open circuit when the light intensity received by the light-absorbing layer is 20 000 Lux, and if the electrolyte contains iodide and triiodide ions, the solar cell unit generates a voltage of about 0.65 V in an open circuit when the light intensity received by the light-absorbing layer is 20 000 Lux. However, the solar cell unit 1 generates a voltage varying at most 0.4 V in an open circuit when the light intensity received by the light-absorbing layer is varying between 200 and 20 000 Lux. The requirement on the voltage conversion of the boost converter depends on the voltage requirement of the rechargeable battery. Most types of rechargeable batteries used for electronic devices for consumer applications require a voltage between 1 and 10 V. The boost converter makes it possible to generate a stable voltage at a level required by the rechargeable battery. Preferably, the boost converter 22 is capable to convert the output voltage and current from the solar cell unit to a voltage level that lies between 1 and 10 V. Different boost converters can be used depending on the required output voltage. Thus, the photovoltaic charger is capable to charge batteries used for many types of electronic devices, such as lithium batteries (3.6V), NiCd and NiMH batteries (1.25 V).

[0193] From tests it has been shown that the solar cell unit is capable to produce a current of at least 15 μA/cm.sup.2 when the light intensity received by the light-absorbing layer is 200 Lux, and a current of at least 1500 μA/cm.sup.2 when the light intensity received by the light-absorbing layer is 20 000 Lux. Thus, the solar cell unit is capable to produce sufficient power to charge batteries of electronic devices in a wide range of light intensities.

[0194] According to some aspects, at least the first conductive layer 12 and the porous substrate 114 are continuously extending through the entire solar cell unit 1. The light-absorbing layer 10 and the second conductive layer 16 extend continuously at least through a main part of the solar cell unit.

[0195] Measurements of generated power per area for different light conditions have been made on an example of a photovoltaic charger of the invention including one single solar cell unit 1. In this example, the solar cell unit 1 has a size of 14.5×23.4 cm, and an active area of 340 cm.sup.2. The electrolyte of the solar cell unit 1 comprises iodide and triiodide ions, and the first and second conductive layers are made of titanium (Ti). The unloaded photovoltaic charger is exposed with light between 200 and 20 000 Lux (lumen per square meter), and the output voltage and output current from the photovoltaic charger is measured. The results of the measurements are shown in table 1 below. The total power generated is determined based on the measured current and voltage, and the generated power per area is determined by dividing the total power with the active area of the solar cell unit.

TABLE-US-00001 TABLE 1 Lux μW/cm2 I sc(μA/cm2) Voc (mV) ff (%) 200 6.2 18 483 72 500 18 44 521 77 1000 37 90 542 76 2000 80 179 565 79 3000 123 266 576 80 5000 208 445 591 79 6000 249 531 600 78 10000 405 880 614 75 20000 730 1700 650 69 Measurements of generated power per active area, current per active area, voltage and fill factors (ff) for light intensities between 200-20 000 Lux for a solar cell unit 1 having an electrolyte comprising iodide (I.sup.−) and triiodide (I.sub.3.sup.−) ions. The content of triiodide is between 1 mM and 20 mM. Iodide works as ox and triiodide works as red.

[0196] The measurements of the performance of the solar cell unit 1 at different light intensities (intensities measured in Lux units) can be done by shining light on the solar cell unit, and simultaneously scanning an applied electrical voltage across the solar cell unit to measure and collect the current-voltage response of the solar cell. The measurements were performed using a warm—white LED as light source.

[0197] The collected IV curve under illumination provides information about the open circuit voltage, short circuit current, fill factor, the power and the power conversion efficiency. By collecting IV curves at different light intensities, it is possible to gather information on the light intensity dependence of the open circuit voltage, short circuit current, fill factor the power and the power conversion efficiency, respectively.

[0198] The result from table 1 is from measurements on a sample of a solar cell unit 1. Measurements on different solar cell units of this type may vary. For example, the generated power per area may from 5 μW/cm.sup.2 to 8 μW/cm.sup.2.

[0199] The light source used for shining light on the solar cell can vary depending on the solar cell application. For indoor applications it could be useful to use fluorescent light bulbs or indoor LED lighting. For solar cell applications that use outdoor light it could be useful to shine light on the solar cell using a solar simulator to generate artificial sunlight.

[0200] The light intensity of the light source can be measured in different ways, for example, using a lux meter or a spectroradiometer positioned at the same position as the solar cell unit in relation to the light source. In this case, the light intensity was measured using a lux meter.

[0201] Table 1 shows the determined power in microwatt per square centimetre (μW/cm.sup.2) for different light intensities measured in lux. As seen from the table, the solar cell unit 1 generates 6.2 μW/cm.sup.2 when the light intensity received by the solar cell unit 1 is 200 Lux, generates 208 μW/cm.sup.2 when the light intensity received by the solar cell unit 1 is 5000 Lux, and generates 730 μW/cm.sup.2 when the light intensity received by the solar cell unit 1 is 20 000 Lux. This shows that the photovoltaic charger is capable of producing more than 5 μW/cm.sup.2, and even more than 5.5 μW/cm.sup.2when the light intensity received by the light-absorbing layer is 200 Lux. This also shows that the photovoltaic charger is capable of producing more than 700 μW/cm.sup.2 when the light intensity received by the light-absorbing layer is 20 000 Lux. Thus, the solar cell unit 1 is at least capable of producing between 5.5 and 700 μW/cm.sup.2 when the light intensity received by the light-absorbing layer is between 200 and 20 000 Lux. The power produced by the photovoltaic charger increases substantially linear when the light intensity received by the light-absorbing layer increases from 200 to 20 000 Lux. Thus, the photovoltaic charger is capable of producing power in a wide range of different light conditions.

[0202] FIG. 5 shows a diagram of generated voltage (mV) for light intensities between 200 and 20 000 Lux based on the measured values of table 1. As seen from the diagram and table 1, the solar cell unit 1 is capable to generate a voltage of 480 mV in an open circuit when the light intensity received by the solar cell unit 1 is 200 Lux. Further, the photovoltaic charger 200 is capable to generate a voltage of 650 mV in an open circuit when the light intensity received by the solar cell unit 1 is 20 000 Lux. As seen from the diagram, the increase of generated voltage is largest between 200 and 3000 Lux. The generated voltage is substantially linear between 3000 and 20 000 Lux. As seen from the table 1, the difference in generated voltage between 200 and 20 000 Lux is only 167 mV. Thus, the solar cell unit 1 generates a voltage varying less than 0.2 V in an open circuit when the light intensity received by the light-absorbing layer is varying between 200 and 20 000 Lux. Accordingly, the difference in generated voltage between 200 and 20 000 Lux is about 35%.

[0203] FIG. 6 shows a diagram of generated current (μA/cm.sup.2) for light intensities between 200 and 20 000 Lux based on the measured values of table 1. As seen from the figure, the current increase linearly.

[0204] FIG. 7 shows a diagram of generated power per area (μW/cm.sup.2) for light intensities between 200 and 20 000 Lux calculated based on the measured values of voltage and current of table 1. As seen from the diagram, the measured power is substantially proportional to the incoming light intensity in the interval 200-20 000 Lux.

[0205] Further measurements of generated power per area for different light conditions have been made on another example of a photovoltaic charger of the invention. In this example, the electrolyte of the solar cell unit 1 comprises copper ions (Cu.sup.+ and Cu.sup.2+0 ), which is the only difference between the photovoltaic chargers measured. The measurement conditions were the same. The unloaded photovoltaic charger 200 is exposed with light between 200 and 20 000 Lux (lumen per square meter), and the output voltage and output current from the photovoltaic charger is measured. The result of the measurements is shown in the table 2 below.

TABLE-US-00002 TABLE 2 Lux μW/cm2 I sc (μA/cm2) Voc (mV) ff (%) 0 0 0 0 0 200 12.8 25 699 72.7 500 38 67 762 74.3 1000 85.4 140 800 76.1 2000 186 290 835 77.1 5000 498 737 881 76.6 10000 1020 1490 915 75.1 20000 2020 2960 943 72.3 30000 2920 4390 954 69.7 40000 3720 5750 958 67.6 50000 4410 7000 958 65.8 Measurements of generated power per area, current per area, voltage and fill factor (ff) for light intensities between 200-20 000 Lux for a solar cell unit 1 having an electrolyte comprising copper ions; Cu.sup.+as red and Cu2.sup.+as ox.

[0206] As seen from the table 2, the solar cell unit 1 generates 12.8 μW/cm.sup.2 when the light intensity received by the solar cell unit 1 is 200 Lux, generates 498 μW/cm.sup.2 when the light intensity received by the solar cell unit 1 is 5000 Lux, and generates 2020 μW/cm.sup.2 when the light intensity received by the solar cell unit 1 is 20 000 Lux. This shows that this photovoltaic charger 200 is capable of producing more than 12 μW/cm.sup.2 when the light intensity received by the light-absorbing layer 10 is 200 Lux. This also shows that the photovoltaic charger 200 is capable of producing more than 2000 μW/cm.sup.2 when the light intensity received by the light-absorbing layer 10 is 20 000 Lux. The power produced by the photovoltaic charger increases substantially linear when the light intensity received by the light-absorbing layer increases from 200 to 20 000 Lux. Thus, the photovoltaic charger 200 is capable of producing power in a wide range of different light conditions.

[0207] FIG. 8 shows a diagram of generated voltage (mV) for light intensities between 200 and 50 000 Lux based on the measured values of table 2. As seen from the diagram and table 2, the solar cell unit 1 is capable of generating a voltage of 699 mV in an open circuit when the light intensity received by the solar cell unit 1 is 200 Lux. Further, the photovoltaic charger 200 is capable to generate a voltage of 943 mV in an open circuit when the light intensity received by the solar cell unit 1 is 20 000 Lux. As seen from the diagram, the generated voltage is substantially linear between 3000 and 50 000 Lux. As seen from the table 2, the difference in generated voltage between 200 and 20 000 Lux is only 244 mV. Accordingly, the difference in generated voltage between 200 and 20 000 Lux is about 35%. The difference in generated voltage between 200 and 50 000 Lux is only 259 mV. Thus, the solar cell unit 1 generates a voltage varying less than 300 mV in an open circuit when the light intensity received by the light-absorbing layer is varying between 200 and 50 000 Lux. Accordingly, the difference in generated voltage between 200 and 50 000 Lux is about 37%.

[0208] FIG. 9 shows a diagram of generated current (μA/cm.sup.2) for light intensities between 200 and 50 000 Lux based on the measured values of table 2. As seen from the figure, the current increases linearly.

[0209] FIG. 10 shows a diagram of generated power per area (μW/cm.sup.2) for light intensities between 200 and 50 000 Lux calculated based on the measured values of voltage and current of table 1. As seen from the diagram, the measured power is substantially proportional to the incoming light intensity in the interval 200-20 000 Lux.

[0210] The present invention is not limited to the embodiments disclosed but may be varied and modified within the scope of the following claims. For example, the second conductive layer 16 can be omitted. Omitting the second conductive layer may reduce the range of different light conditions in which the solar cell unit can produce enough power for powering a device. However, in some applications the light conditions do no vary that much and a solar cell unit capable to produce power in a smaller range is enough.