Solar cell

Abstract

A solar cell comprising a substrate, an active layer comprising a perovskite material or a polymer material, the active layer being configured to absorb at least a portion of light incident on the solar cell and to convert the absorbed portion of light into a plurality of charge carriers, a first electrode configured to be opaque and / or to reflect light transmitted through the active layer towards the active layer, and a second electrode configured to be transparent to the portion of light to be absorbed by the active layer, wherein the active layer is arranged between the first and second electrodes and the first electrode is arranged between the substrate and the active layer, and wherein the solar cell is configured such that a work function of the first electrode is different from a work function of the second electrode.

Description

[0001] SOLAR CELL

[0002] FIELD

[0003] The present disclosure relates to a solar cell, a method of manufacturing the solar cell and associated devices and / or items.

[0004] BACKGROUND

[0005] Internet of things (loT) devices have become more popular in recent years with the number of loT devices in consumer hands exceeding several tens of billions. Wearable devices or technologies have seen a similar growth in popularity as loT devices. However, sustainably powering these devices can be challenging. Photovoltaic devices may have the potential to generate electricity for such devices and / or other devices. A photovoltaic device may be configured to convert the energy of light into electricity using the photovoltaic effect. loT devices may typically be used in an indoor environment whereas wearable devices may be used in an indoor and / or outdoor environment. There is a need for an improved photovoltaic device that can be used, for example in such devices indoors and / or outdoors.

[0006] This background serves only to set a scene to allow a person skilled in the art to better appreciate the following description. Therefore, none of the above discussion should necessarily be taken as an acknowledgement that that discussion is part of the state of the art or is common general knowledge. One or more aspects / embodiments of the disclosure may or may not address one or more of the background issues.

[0007] SUMMARY

[0008] According to a first aspect of the present disclosure there is provided a solar cell comprising a substrate, an active layer comprising a perovskite material or a polymer material, the active layer being configured to absorb at least a portion of light incident on the solar cell and to convert the absorbed portion of light into a plurality of charge carriers, a first electrode configured to be opaque and / or to reflect light transmitted through the active layer towards the active layer, and a second electrode configured to be transparent to the portion of light to be absorbed by the active layer, wherein the active layer is arranged between the first and second electrodes and the first electrode is arranged between the substrate and the active layer, and wherein the solar cell is configured such that a work function of the first electrode is different from a work function of the second electrode. By configuring the second electrode to be transparent to the portion light to be absorbed by the active layer, arranging the active layer between the first and second electrodes and arranging the first electrode between the substrate and the active layer top illumination of the solar cell may be allowed. This may facilitate the use and / or integration of the solar cell in a wearable device, loT device, an item of furnishing or another device or item.

[0009] Additionally or alternatively, by configuring the second electrode to be transparent to the portion light to be absorbed by the active layer, configuring the first electrode to be opaque and / or to reflect light transmitted through the active layer towards the active layer, arranging the active layer between the first and second electrodes and / or arranging the first electrode between the substrate and the active layer, an opaque substrate may be used. This in turn may facilitate the use or integration of the solar cell in a wearable device, loT device, an item of furnishing or another item or device.

[0010] Additionally or alternatively, by configuring the solar cell such that a work function of the first electrode is different from a work function of the second electrode, an increased built-in electrical field may be present in the solar cell. The increased built-in electrical field may result in an increased separation of the charge carriers in the active layer, e.g. in use, and as such, in an increased performance of the solar cell.

[0011] The solar cell, e.g. at least one of the first and second electrodes, may be configured such that the at least one of the first and second electrodes comprises or defines an energy level that facilitates and / or allows for a collection of a portion of the plurality of charge carriers, e.g. at least one of a plurality of holes and a plurality of electrons. The solar cell, e.g. at least one other of the first and second electrode may be configured such that the at least one other of the first and second electrodes comprises or defines an energy level that facilitates and / or allows for a collection of another portion of the plurality of charge carriers, e.g. at least one other of the plurality of holes and the plurality of electrons.

[0012] The solar cell, e.g. the first and second electrodes, may be configured such that the work function of at least one of the first and second electrodes is lower than the work function of at least one other of the first and second electrodes. This may allow for an enhanced or improved collection of the plurality of charge carriers from the active layer.

[0013] The substrate may comprise a rigid substrate. The substrate may comprise a flexible substrate. The flexible substrate may comprise a layer of textile material or a layer of polymer material, such as a layer of plastic material. The plastic material may comprise polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyimide (PI) or another plastic material.

[0014] The flexible substrate may comprise an interlayer. The interlayer may be arranged between the layer of textile material or the layer of polymer material and the first electrode.

[0015] The first electrode may comprise a conductive material. The second electrode may comprise a conductive material. The conductive material of the second electrode may be different from the conductive material of the first electrode.

[0016] The first electrode may comprise a single layer of the conductive material. The conductive material of the first electrode may comprise at least one of a metal material, such as aluminium, a transition metal material, such as nickel, and / or a carbon material. The carbon material may comprise graphite, graphene, carbon nanotubes and / or any other suitable conductive carbon material. The first electrode may be formed from a carbon paste.

[0017] Alternatively, the first electrode may comprise a plurality of layers. At least one of the plurality of layer may comprise the conductive material. The plurality of layers may comprise a plurality of conductive materials.

[0018] The conductive material of the second electrode may comprise at least one of a metal material and / or a transition metal material, such as gold, silver and / or the like.

[0019] The second electrode may comprise one or more layers of a semiconductor material or dielectric material. The second electrode may be configured as a dielectric- metal-dielectric transparent electrode. For example, the semiconductor material may comprise molybdenum oxide. The dielectric material may comprise tungsten oxide.

[0020] The solar cell may be configured such that light is incident on the second electrode. The solar cell may be configured such that light or at least a portion thereof passes through the second electrode before being incident on the active layer.

[0021] The solar cell may comprise an electron transport layer. The electron transport layer may be arranged between the first electrode and the active layer. The electron transport layer may comprise an oxide material, such as tin oxide (SnC>2), titanium dioxide (TiC>2), zinc oxide (ZnO) or the like.

[0022] The solar cell may comprise a hole transport layer. The hole transport layer may be arranged between the active layer and the second electrode. The hole transport layer may comprise an organic compound, such as Spiro-MeOTAD (CsiHesN^s) or the like, or a polymer material, such as Poly(3-hexylthiophene) (P3HT), Poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine (PTAA), Poly(N,N'-bis-4-butylphenyl- N,N'-bisphenyl)benzidine (PolyTPD) or the like. Additionally or alternatively, the hole transport layer may comprise an inorganic material, such as inorganic polymer material. The inorganic polymer material may comprise Copper(l) thiocyanate (CuSCN) or the like.

[0023] The perovskite material or polymer material may be configured such that a bandgap of the perovskite material or polymer material is between about 1 .5 eV and about 2.3 eV.

[0024] The perovskite material may comprise methylammonium lead halide. For example, methylammonium lead halide may comprise methylammonium lead trihalide, such as methylammonium lead iodide, methylammonium lead bromide, methylammonium iodide bromide or methylammonium lead chloride or combinations thereof.

[0025] The polymer material may comprise poly(3-hexylthiophene): [6,6]-phenyl C61- butyric acid methylester (P3HT: PCBM) or poly(3-hexylthiophene): indene-C60 bisadduct (P3HT: ICBA), a combination of PM6: Y6 and PM6: F-2CI, PBDB-T-2F:BTP- 4F-BTP-M, PBODT:PC71 BM:ITIC and / or another polymer material.

[0026] According to a second aspect of the present disclosure there is provided a method of manufacturing a solar cell, the method comprising providing a substrate, forming a first electrode, forming an active layer comprising a perovskite material or a polymer material, the active layer being configured to absorb at least a portion of light incident on the solar cell and to convert the absorbed portion of light into a plurality of charge carriers, and forming a second electrode, the second electrode being configured to be transparent to the portion of light to be absorbed by the active layer and the first electrode being configured to be opaque and / or to reflect light transmitted through the active layer towards the active layer, wherein the active layer is formed between the first and second electrodes and the first electrode is formed between the substrate and the active layer, and wherein the solar cell is configured such that a work function of the first electrode is different from a work function of the second electrode.

[0027] The substrate may comprise a rigid substrate or a flexible substrate.

[0028] The flexible substrate may comprise a layer of textile material or a layer of polymer material, such as a layer of plastic material. The flexible substrate may comprise an interlayer. The interlayer may be arranged between the textile material or the layer of polymer material and the first electrode. The first electrode may comprise a conductive material. The first electrode may be formed as single layer of the conductive material. The conductive material of the first electrode may comprise at least one of a metal material, such as aluminium, a transition metal material, such as nickel, and / or a carbon material. For example, the first electrode may be formed from a carbon paste.

[0029] Alternatively, the first electrode may comprise or be formed from a plurality of layers. At least one of the plurality of layer may comprise the conductive material. The plurality of layers may comprise a plurality of conductive materials.

[0030] Any features of the first aspect may also apply to the second aspect.

[0031] According to a third aspect of the present disclosure there is provided a solar cell comprising a substrate, an active layer comprising a perovskite material, the active layer being configured to absorb at least a portion of light incident on the solar cell and to convert the absorbed portion of light into a plurality of charge carriers, a first electrode configured to be opaque and / or to reflect light transmitted through the active layer towards the active layer, and a second electrode configured to be transparent to the portion of light to be absorbed by the active layer, wherein the active layer is arranged between the first and second electrodes and the first electrode is arranged between the substrate and the active layer.

[0032] The solar cell of the third aspect may comprise any of the features of the solar cell of the first aspect.

[0033] According to a fourth aspect of the present disclosure there is provided an loT (Internet of Things) and / or wearable device comprising a solar cell according to the first or third aspect.

[0034] According to a fifth aspect of the present disclosure there is provided an item of furnishing comprising a solar cell according to the first or third aspect.

[0035] According to a sixth aspect of the present disclosure there is provided a solar cell comprising a substrate, an active layer comprising a perovskite material or a polymer material, the active layer being configured to absorb at least a portion of light incident on the solar cell and to convert the absorbed portion of light into a plurality of charge carriers, a first electrode configured to reflect light transmitted through the active layer towards the active layer, and a second electrode configured to be transparent to the portion of light to be absorbed by the active layer, wherein the active layer is arranged between the first and second electrodes and the first electrode is arranged between the substrate and the active layer, and wherein the first and second electrodes are configured such that a work function of the first electrode is different from a work function of the second electrode.

[0036] The solar cell of the sixth aspect may comprise any of the features of the solar cell of the first aspect.

[0037] According to a seventh aspect there is provided a solar cell comprising a substrate, an active layer comprising a perovskite material or a polymer material, the active layer being configured to absorb at least a portion of light incident on the solar cell and to convert the absorbed portion of light into a plurality of charge carriers, a first electrode configured to be transparent to the portion of light to be absorbed by the active layer, and a second electrode, wherein the active layer is arranged between the first and second electrodes and the first electrode is arranged between the substrate and the active layer, and wherein the solar cell is configured such that a work function of the first electrode is different from a work function of the second electrode.

[0038] The solar cell of the seventh aspect may comprise any of the features of the solar cell of the first aspect.

[0039] The first electrode of the seventh aspect may comprise any features of the second electrode according to the first aspect. Alternatively or additionally, the conductive material of the first electrode may comprise a transparent conductive oxide, such as indium tin oxide or another transparent conductive oxide.

[0040] The second electrode of the seventh aspect may comprise any features of the first electrode according to the first aspect.

[0041] The above summary is intended to be merely exemplary and non-limiting. The disclosure includes one or more corresponding aspects, embodiments or features in isolation or in various combinations whether or not specifically stated (including claimed) in that combination or in isolation. It should be understood that features defined above in accordance with any aspect of the present disclosure or below relating to any specific embodiment of the disclosure may be utilised, either alone or in combination with any other defined feature, in any other aspect or embodiment or to form a further aspect or embodiment of the disclosure.

[0042] BRIEF DESCRIPTION OF DRAWINGS

[0043] Some preferred embodiments of the disclosure will now be described by way of example only and with reference to the accompanying drawings, in which:

[0044] Figure 1 schematically depicts an exemplary solar cell, the solar cell comprising a flexible substrate, which includes a layer of textile material; Figure 2 depicts a graph of a measured current density in dependency on a voltage applied to the solar cell of Figure 1 ;

[0045] Figure 3 schematically depicts another exemplary solar cell, the solar cell comprising a flexible substrate, which includes a layer of textile material;

[0046] Figure 4A depicts a graph of a measured current density in dependency on a voltage applied to the solar cell of Figure 3 under one sun illumination;

[0047] Figure 4B depicts another graph of a measured current density in dependency on a voltage applied to the solar cell of Figure 3 under indoor illumination;

[0048] Figure 4C depicts a graph of a measured current density in dependency of time for a constant voltage applied to the solar cell of Figure 3 under one sun illumination;

[0049] Figure 4D shows another graph of a measured current density in dependency of time for a constant voltage applied to the solar cell of Figure 3 under indoor illumination;

[0050] Figure 5 schematically depicts another exemplary solar cell, the solar cell may comprise a flexible substrate, which may include a layer of polymer material, or a rigid substrate, which may include a glass substrate;

[0051] Figure 6A depicts a graph of a measured current density in dependency on a voltage applied to the solar cell of Figure 5 under one sun illumination;

[0052] Figure 6B depicts another graph of a measured current density in dependency on a voltage applied to the solar cell of Figure 5 under indoor illumination;

[0053] Figure 6C depicts a graph of a measured current density in dependency of time for a constant voltage applied to the solar cell of Figure 5 under one sun illumination;

[0054] Figure 6D shows another graph of a measured current density in dependency of time for a constant voltage applied to the solar cell of Figure 5 under indoor illumination;

[0055] Figure 7A schematically depicts another exemplary solar cell, the solar cell comprising a flexible substrate, which includes a layer of textile material;

[0056] Figure 7B schematically depicts another exemplary solar cell, the solar cell may comprise a flexible substrate, which may include a layer of polymer material, or a rigid substrate, which may include a glass substrate;

[0057] Figure 8 depicts a flow chart illustrating in overview a method of manufacturing a solar cell;

[0058] Figure 9A schematically depicts an exemplary wearable device comprising the solar cell of any one of Figures 1 , 3, 5, 7A or 7B; Figure 9B schematically depicts an exemplary loT device comprising the solar cell of any one of Figures 1 , 3, 5, 7A or 7B;

[0059] Figure 9C schematically depicts an item of furnishing comprising the solar cell of any one of Figures 1 , 3, 5, 7A or 7B;

[0060] Figure 10 schematically depicts another exemplary solar cell;

[0061] Figure 11A depicts a graph of a measured current density in dependency on a voltage applied to the solar cell of Figure 10 under one sun illumination; and

[0062] Figure 11 B depicts another graph of a measured current density in dependency on a voltage applied to the solar cell of Figure 10 under indoor illumination.

[0063] DETAILED DESCRIPTION OF DRAWINGS

[0064] Figure 1 schematically shows an exemplary solar cell 2. The solar cell 2 may also be referred to as a photovoltaic device. The solar cell 2 comprises a substrate 4. The solar cell 2 comprises an active layer 6. In the following description, the active layer 6 comprises a perovskite material. The solar cell 2 may be referred to as a perovskite solar cell. However, it will be appreciated that in other embodiments, the active layer may comprise a different material, such as a polymer material, as will be described below. The active layer 6 is configured to absorb at least a portion of light incident on the solar cell 2 and to convert the absorbed portion of light into a plurality of charge carriers, e.g. using the photovoltaic effect. It will be appreciated that the active layer 6 may only convert a portion of the absorbed light into the charge carriers, e.g. due to recombination losses, thermalisation losses, junction losses, transmission losses and / or other loss mechanism. The plurality of charge carriers may comprise a plurality of holes and a plurality of electrons. The portion of light may be understood as comprising light, e.g. photons, having an energy larger than a bandgap of the perovskite material. The portion of light may also be referred to as a portion of radiation, e.g. electromagnetic radiation, and / or a portion of visible light. The solar cell 2 may be considered as being configured to convert photon power or optical power into electrical power.

[0065] The perovskite material may comprise methylammonium lead halide. In this embodiment, methylammonium lead halide comprises methylammonium lead trihalide, such as methylammonium lead iodide. In other embodiments, methylammonium lead trihalide may comprise methylammonium lead bromide, methylammonium iodide bromide or methylammonium lead chloride or combinations thereof. The perovskite material may be configured such that the bandgap of the perovskite material is between about 1.5 eV and about 2.3 eV, such as about 1.56 eV. For example, the bandgap of the perovskite material may be controlled by selecting the lead halide and / or controlling an amount of the lead halide. As such, in other embodiment, the perovskite material may have a bandgap that is different from about 1.56 eV. A thickness of the active layer 6 may be between about 200 nm and about 700 nm, such as between about 400 nm and about 600 nm or between about 300 nm and 500 nm. However, it will be appreciated that in other embodiments, a thickness of the active layer may be less than 200 nm and / or more than 700 nm.

[0066] The solar cell 2 comprises a first electrode 8. In this embodiment, the first electrode 8 is configured to reflect light incident thereon. For example, the first electrode 8 may be configured to reflect light transmitted through the active layer 6 towards the active layer 6. This may allow for light that was not fully absorbed by the active layer to be reflected towards to active layer 6 for absorption. As such, the first electrode 8 may allow for an increase in the amount of light absorbed by the active layer 6. The first electrode 8 may be configured to at least reflect light having a photon energy equal to or larger than the bandgap of the active layer 6. However, it will be appreciated that the first electrode 8 may be configured to additionally reflect light having a photon energy less than the bandgap of the active layer 6.

[0067] The first electrode 8 may also be configured to be opaque, e.g. to light incident on the solar cell 2. For example, the first electrode 8 may be configured to prevent light transmitted through the active layer 6 from being transmitted through the first electrode 8, e.g. to the substrate 4. It will be appreciated that in other embodiments, the first electrode may be only opaque. In such other embodiments, the first electrode may be considered to be non-reflective, e.g. not capable of reflecting light incident thereon.

[0068] The solar cell 2 comprises a second electrode 10. The second electrode 10 is configured to be transparent to at least the portion of light to be absorbed by the active layer 6. For example, the second electrode 10 may be configured such that at least the portion of light to be absorbed by the active layer 6 passes through the second electrode 10, e.g. to the active layer 6. The solar cell 2 is configured such that light, e.g. at least the portion of light to be absorbed by the active layer 6, is incident on the second electrode 10. As can be seen in Figure 1, the active layer 6 is arranged between the first and second electrodes 8, 10. The first electrode 8 is arranged between the substrate 4 and the active layer 6. The first electrode 8 may also be referred to as a bottom electrode. The second electrode 10 may also be referred to as a top electrode. By configuring the second electrode 10 to be transparent to at least the portion light to be absorbed by the active layer 6, arranging the active layer 6 between the first and second electrodes 8, 10 and arranging the first electrode 8 between the substrate 4 and the active layer 6 top illumination of the solar cell 2 may be allowed. This may facilitate the use and / or integration of the solar cell 2 in a wearable device, loT device, an item of furnishing or another device or item. Additionally or alternatively, by configuring the second electrode 10 to be transparent to at least the portion light to be absorbed by the active layer 6, configuring the first electrode 8 to reflect light transmitted through the active layer 6 towards the active layer 6, arranging the active layer 6 between the first and second electrodes 8, 10 and / or arranging the first electrode 8 between the substrate 4 and the active layer 6, an opaque substrate, such as a substrate comprising a textile material or polymer material, may be used. This in turn may facilitate the use or integration of the solar cell 2 in a wearable device, loT device, an item of furnishing or another item or device, as will be described below.

[0069] In this embodiment, the substrate 4 comprises a flexible substrate. By providing the substrate 4 with a flexible substrate, the use of the solar cell 2 in, for example the wearable device, the item of furnishing or the other item or device may be facilitated.

[0070] In this embodiment, the substrate 4 comprises a layer 4a of textile material. However, it will be appreciated that in other embodiments, the substrate may comprise a layer of polymer material, such as a layer of plastic material. The plastic material may comprise polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyimide (PI) or another plastic material.

[0071] The substrate 4 comprises an interlayer 4b. The interlayer 4b is arranged between the layer 4a of textile material and the first electrode 8. The interlayer 4b may be arranged on the layer of textile material, e.g. to facilitate the formation of the first electrode 8 on the layer 4a of textile material. The textile material may comprise a woven fabric, such as a woven polyester cotton (65 / 35). However, it will be appreciated that other textile materials may be used in other embodiments. The interlayer 4b may have a thickness between about 2 pm and 100 pm. The interlayer 4b may comprise a polymer material, such as polyurethane or another polymer material. For example, the interlayer 4b may be formed from a polyurethane-based interface paste, such as Fabink-UV-IF1, supplied by Smart Fabric Ink, Ltd. The interlayer 4b may be formed by screen printing the polymer material on the layer 4a of textile material, e.g. to planarise the layer 4a of textile material. However, it will be appreciated that in other embodiments, the solar cell may not comprise the interlayer and the first electrode may be formed directly on the substrate, e.g. the layer of textile material, the layer of polymer material or another substrate.

[0072] The first electrode 8 may comprise a plurality of layers of conductive material. For example, the first electrode 8 comprises a first layer 8a of a first conductive material and a second layer 8b of a second conductive material. The first and second conductive materials may be different. The first layer 8a of the first conductive material and the second layer 8b of the second conductive material may each comprise a metal material, a transition metal material or the like.

[0073] In this embodiment, the first layer 8a of the first conductive material may comprise gold and the second layer 8b of the second conductive material may comprise silver. A thickness of the first layer 8a of the first conductive material may be between about 5 nm and 20 nm, such as about 10 nm. A thickness of the second layer 8b of the second conductive material may be between about 50 nm and 200 nm, such as about 100 nm. The first layer 8a of the first conductive material may be arranged to cover, e.g. completely cover, the substrate 4 and / or to facilitate the formation of the second layer 8b of the second conductive material thereon. For example, the first layer 8a of the first conductive material may be deposited on the substrate 4 to improve a wettability of the second layer 8b of the second conductive material, e.g. during manufacture of the solar cell 2. The first electrode 8a disclosed herein is not limited to comprising the first layer of the first conductive material and the second layer of the second conductive material described above. It will be appreciated that in other embodiments, the first electrode may comprise a single layer of conductive material or more than two layers of conductive material and / or more than two different conductive materials.

[0074] The solar cell 2 may comprise an electron transport layer 12. The electron transport layer 12 may be arranged between the first electrode 8 and the active layer 6. The electron transport layer 12 may be configured to facilitate and / or increase a transport of electrons generated in the active layer 6 to the first electrode 8a and / or to reduce a recombination of the charge carriers. In this embodiment, the electron transport layer 12 comprises an oxide material, such as tin oxide (SnC>2). However, it will be appreciated that in other embodiments, the electron transport layer may comprise a different material, such as a different oxide material. For example, in such other embodiments, the oxide material may comprise titanium dioxide (TiC>2) , zinc oxide (ZnO) or the like. A thickness of the electron transport layer 12 may be between about 10 nm and 50 nm, such as about 30 nm. The solar cell 2 may comprise a hole transport layer 14. The hole transport layer 14 may be configured to facilitate the extraction and / or transport of holes generated in the active layer 6 to the second electrode 10 and / or to prevent the transport of electrons generated in the active layer 6 to the second electrode 10. The hole transport layer 14 may be arranged between the active layer 6 and the second electrode 10. The hole transport layer 14 may be configured to be transparent to at least the portion of light to be absorbed by the active layer 6. The hole transport layer 14 may comprise an organic compound, such as Spiro-MeOTAD (CsiHesl^UOs) or the like. A thickness of the hole transport layer 14 may be between about 150 nm and 400 nm, such as about 280 nm. By selecting the thickness of the hole transport layer 14 to be between about 150 nm and 400 nm, a roughness of the layers of the solar cell 2, e.g. due to the layer of textile material, may be decreased. This may result in a decreased risk of forming a short circuit in the solar cell.

[0075] However, it will be appreciated that in other embodiments, the hole transport layer may comprise another organic material. The other organic material may comprise a polymer material, such as Poly(3-hexylthiophene) (P3HT), Poly[bis(4-phenyl)(2,4,6- trimethylphenyl)amine (PTAA), Poly(N,N'-bis-4-butylphenyl-N,N'-bisphenyl)benzidine (PolyTPD) or the like. In such other embodiments, a thickness of the hole transport layer may be below 150 nm. For example, in such other embodiments, the thickness of the hole transport layer may be between about 30 nm and 100 nm, such as about 50 nm. In other embodiments, the hole transport layer may comprise an inorganic material, such as inorganic polymer material. The inorganic polymer material may comprise Copper(l) thiocyanate (CuSCN) or the like. In such other embodiments, a thickness of the hole transport layer may be below 150 nm. For example, in such other embodiments, the thickness of the hole transport layer may be between about 30 nm and 100 nm, such as about 40 nm.

[0076] As can be seen in Figure 1 , the active layer 6 is arranged between the electron transport layer 12 and the hole transport layer 14.

[0077] In the embodiment shown in Figure 1 , the second electrode 10 comprises a plurality of layers 10a-10d. The layers 10a-10d may be configured to be transparent to at least the portion of light to be absorbed by the active layer 6, e.g. to allow at least a portion of light incident on the solar cell 2 to pass through the second electrode 10 to the active layer 6.

[0078] In this embodiment, the second electrode 10 comprises four layers 10a-10d. One or more of the layers of the second electrode 10 may comprise a conductive material. One or more other layers of the second electrode 10 may comprise a semiconductor material or a dielectric material. The conductive material of each of the one or more layers may be different or the same.

[0079] For example, the second electrode 10 comprises a first layer 10a. The first layer 10a of the first may be formed or arranged on the hole transport layer 14. The first layer 10a may comprise a semiconductor material, such as molybdenum oxide (MoOx) or the like. The use of molybdenum oxide on a hole transport layer 14 comprising, e.g. Spiro- MeOTAD, may allow and / or improve the extraction and / or transport of holes generated in the active layer 6 to the second electrode 10. A thickness of the first layer 10a may be between about 5 nm and 30 nm, such as about 10 nm.

[0080] The second electrode 10 comprises a second layer. The second layer 10b may be formed or arranged on the first layer 10a. The second layer 10b of may comprise a conductive material. For example, the second layer 10b may comprise a metal material or a transition metal material, such as gold or the like. A thickness of the second layer 10b may be between about 0.5 nm and 5 nm, such as about 1 nm.

[0081] The second electrode 10 comprises a third layer 10c. The third layer 10c may be formed or arranged on the second layer 10b. The third layer 10c may comprise a conductive material. For example, the third layer 10c may comprise a metal material or a transition metal material, such as silver or the like. A thickness of the third layer 10c may be between about 5 nm and 30 nm, such as about 10 nm.

[0082] The second electrode 10 comprises a fourth layer 10d. In this embodiment, the first and fourth layers 10a, 10d comprises the same material. However, it will be appreciated that in other embodiments, the first and fourth layers may comprise different materials.

[0083] The fourth layer 10d may be formed or arranged on the third layer 10c. A thickness of the fourth layer 10d may be between about 5 nm and 40 nm, such as about 20 nm. In this embodiment, both the first and fourth layers 10a, 10d comprise a semiconductor material. However, it will be appreciated that in other embodiments, one or more of the layers of the second electrode may comprise a dielectric material, such as tungsten oxide (WO3). The second electrode 10 may be considered as a dielectric- metal-dielectric (DMD) transparent electrode.

[0084] It will be appreciated that in other embodiments, the second electrode may be differently implemented. For example, in such other embodiments, the second electrode may comprise more or less than four layers, one or more of the layers may comprise a material that is different from the exemplary materials described herein and / or one or more of the layers may comprise a thickness that is different from the exemplary thicknesses described herein.

[0085] In this embodiment, the exemplary first and second electrodes 8,10 may be formed without indium tin oxide. This may facilitate the manufacture of the solar cell 2, increase the flexibility and / or reduce costs of the manufacture of the solar cell 2.

[0086] The solar cell 2 shown in Figure 1 may be considered as defining an n-i-p structure.

[0087] Figure 2 shows a graph of a measured current density in dependency on a voltage applied to the solar cell 2 shown in Figure 1. The current density was measured under one sun illumination (AM 1.5G, 100 mW / cm2) of the solar cell 2. The current density was measured in a Forward Scan (FS), during which the voltage across the solar cell 2 was increased from zero to the open-circuit voltage. From the measured current density and the applied voltage, a power conversion efficiency of about 0.03% was determined. The power conversion efficiency may be understood as a ratio of electrical power to optical power.

[0088] From the graph shown in Figure 2, an open-circuit voltage was determined as about 0.49 V. The open-circuit voltage was determined for a current density equal to zero. The open-circuit voltage may be considered as a maximum voltage available from the solar cell 2 and / or as a measure of recombination of charge carriers in the solar cell 2.

[0089] From the graph shown in Figure 2, a short-circuit current density was determined as about 0.13 mA / cm2. The short-circuit current density was determined for a voltage across the solar cell 2 being equal to zero. The short-circuit current density may be considered as a maximum current density available from the solar cell 2.

[0090] A fill factor was determined as about 52%. The fill factor may be considered as a measure of the realisable power output of the solar cell 2.

[0091] Figure 3 schematically shows another exemplary solar cell 2. The solar cell 2 shown in Figure 3 is similar to that shown in Figure 1. As such, any features described in relation to the solar cell 2 shown in Figure 1 may also apply to the solar cell 2 shown in Figure 3. Only differences will be described in the following.

[0092] In the embodiment shown in Figure 3, the first electrode 8 comprises a single layer of conductive material. This may reduce a number of layers of the solar cell 2, which in turn may facilitate the manufacture of the solar cell 2 and / or reduce costs of manufacture of the solar cell 2. However, it will be appreciated that alternatively the first electrode may comprise a plurality of layers. In this embodiment, the solar cell 2 is configured such that a work function of the first electrode 8 is different from a work function of the second electrode 10. For example, the first and second electrodes 8, 10 can be configured such that a work function of the first electrode 8 is different from a work function of the second electrode 10. This may result in an increased built-in electrical field. This in turn may result in an increased separation of the charge carriers in the active layer 6, e.g. in use, and as such, in an increased performance of the solar cell 2. The conductive material of the first electrode 8 may be different from a conductive material of the second electrode 10. The conductive material of the first electrode 8 comprises a metal material, such as aluminium or the like, or a transition metal material, such as nickel or the like. For example, the use of aluminium may allow for an improved wettability of the oxide material of the electron transport layer 12 and / or the perovskite material of the active layer 6. In embodiments where the conductive material of the first electrode 8 comprises the metal material or transition metal material, the first electrode 8 may be reflective, as described above.

[0093] In some embodiments, the conductive material comprises additionally or alternatively a carbon material. The carbon material may comprise graphite, graphene, carbon nanotubes and / or any other suitable conductive carbon material. The first electrode may be formed from a carbon paste. In embodiments where the conductive material of the first electrode comprises the carbon material, the first electrode may be referred to as a carbon electrode, carbon paste electrode or the like. In embodiments where the conductive material of the first electrode comprises only the carbon material, the first electrode may be opaque and non-reflective.

[0094] A thickness of the first electrode 8 may be between about 50 nm and 30 pm. For example, when the conductive material comprises the metal material or the transition metal material, the thickness of the first electrode 8 may be between 50 nm and 200 nm, such as about 100 nm. For example, when the conductive material comprises the carbon material, the thickness of the first electrode 8 may be increased relative the thickness of the first electrode 8, when the conductive material comprises the metal material or the transition metal material. When the conductive material comprises the carbon material, the thickness of the first electrode 8 may be between 5 pm and 30 pm, such as about between 10 pm and 20 pm. The increased thickness of the first electrode 8 may decrease or avoid a roughness of the active layer 6, which may be due to the layer 4a of textile material. Additionally or alternatively, the increased thickness of the first electrode 8 may prevent or decrease a formation of shunt paths, e.g. due to a roughness of the layer 4a of textile material. This may result in a decreased risk of forming a short-circuit paths in the solar cell 2. The use of the carbon material as a conductive material of the first electrode 8 may decrease costs for manufacturing the solar cell and / or may allow for the use of large-area processes for manufacturing the solar cell, as will be described below.

[0095] The solar cell 2 is configured such that a work function of the first electrode 8 is different from a work function of the second electrode 10. For example, the conductive materials of the first and second electrodes 8, 10 may be selected such that the work function of the first electrode 8 is lower than the work function of the second electrode 10. For example, aluminium has a work function of about 4.2 eV. As described above, the second electrode 10 may comprise molybdenum oxide, which has a work function of about 5.7 eV, gold, which has a work function of about 5.1 eV, and silver, which has a work function of about 4.7 eV. The exemplary values of the work functions described above correspond to the work function values of the individual materials of the first and second electrodes 8, 10. It will be appreciated the work function of each of the first and second electrode 8, 10 may be different, when these materials are part of the solar cell 2. This may be because the solar cell may be considered as defining a heterostructure, e.g. due to one or more interface properties, dipoles and / or surface potentials that may be present in the solar cell. The materials of the first and second electrode 8, 10 may be selected such that a difference between the respective work functions of the first and second electrodes 8, 10, when the first and second electrodes 8, 10 are implemented in the solar cell, corresponds, e.g. substantially corresponds, to an opencircuit voltage of the solar cell. The materials of the first and second electrode 8, 10 may be selected such that the difference between the respective work functions of the first and second electrodes 8, 10, e.g. when the first and second electrodes 8, 10 are implemented in the solar cell, is in alignment with the conduction band energy level and the valence band energy level of the perovskite material of the active layer 6. It will be appreciated that in other embodiments the second electrode may be configured to have a work function that is lower than a work function of the first electrode. In such other embodiments, the solar cell may be considered as defining a p-i-n structure. In such other embodiments, the electron transport layer and / or hole transport layer may be differently configured. For example, a thickness of at least one or both of the electron transport layer and the hole transport layer may be larger than the thickness of the electron transport layer and the hole transport layer described herein. It will also be appreciated that other layers of the solar cell, such as the electron transport layer and / or the hole transport layer may vary an effective work function of the first and / or second electrodes.

[0096] Additionally or alternatively, the conductive material of the first electrode 8 may be processed such that a work function of the first electrode 8 is different from, e.g. lower than, the work function of the second electrode 10. For example, the carbon material has a work function of about 5.1 eV. The first electrode 8 may be configured to include at least one further layer.

[0097] In some embodiments, the further layer may comprise a further conductive material, such as a metal material, a transition metal material, or another conductive material. The metal material or the transition metal material may comprise any of the exemplary metal materials or transition metal materials described herein. The further conductive material of the further layer may be selected or configured such that a work function of the first electrode 8 is decreased relative the work function of the carbon material. For example, the further conductive material may comprise aluminium, which has a work function of about 4.2 eV. In this embodiment, an effective work function of the first electrode 8 may be about 4.2 eV. The further layer may be formed or arranged to be adjacent to the electron transport layer 12. For example, the further layer may be formed between a layer of carbon material and the electron transport layer 12. This may allow for the formation of a first electrode 8 that is configured to reflect light transmitted through the active layer 6 towards the active layer 6. The further layer may have a thickness between about 80 nm and about 150 nm, such as about 100 nm.

[0098] In some embodiment, the further layer may comprise a polymer material, such as polyethylenimine (PEI) or the like. The further layer may be referred to as a work function modifier layer, e.g. a low-work function modifier layer. The further layer may be configured to reduce a work function of the conductive material of the first electrode 8. The further layer may be formed between the layer of carbon material and the electron transport layer 12. The further layer may have a thickness between about 5 nm and about 30 nm.

[0099] In some embodiments, the electron transport layer 12 comprises tin oxide, as described above. The use of this exemplary material for the electron transport layer 12 may result in a decreased effective work function of the first electrode 8, which will be described in more detail below. As such, the electron transport layer and / or the hole transport layer may be configured such that a work function of the first electrode 8 is different from a work function of the second electrode 10. Figure 4A shows a graph of a measured current density in dependency on a voltage applied to the solar cell 2 shown in Figure 3. As described above, in the embodiment shown in Figure 3, the substrate 4 comprises the layer of textile material 4a and the interlayer 4b. The current density was measured under one sun illumination (AM 1.5G, 100 mW / cm2) of the solar cell 2. The current density was measured in a Forward Scan (FS), during which the voltage across the solar cell 2 was increased from zero to the open-circuit voltage. The current density was also measured in a Reverse Scan (RS) during which the voltage in the solar cell 2 was decreased from the open-circuit voltage to zero.

[0100] From the measured current density and the applied voltage, a power conversion efficiency of about 0.09 % was determined in the Forward Scan and a power conversion efficiency of about 0.04 % was determined in the Reverse Scan.

[0101] The open-circuit voltage was determined as about 1V in the Forward Scan and as about 0.6 V in the Reverse Scan. The short-circuit current density was determined as about 0.17 mA / cm2in the Forward Scan and as about 0.18 mA / cm2in the Reverse Scan. The fill factor was determined as about 50% in the Forward Scan and as about 38% in the Reverse Scan.

[0102] The power conversion efficiency, open-circuit voltage and short-circuit current density of the exemplary solar cell 2 shown in Figure 3 are increased relative to the power conversion efficiency, open-circuit voltage and short-circuit current density of the exemplary solar cell 2 shown in Figure 1. This may be due to the increase in the built-in electric field, as described above. As such, by selecting the conductive material of the first electrode 8 such that the work function of the first electrode 8 is different from the work function of the second electrode 10, the performance of the solar cell 2 may be improved.

[0103] Figure 4B shows another graph of a measured current density in dependency on a voltage applied to the solar cell 2 shown in Figure 3. The current density was measured under indoor illumination of the solar cell 2 by a white light emitting diode using an irradiance of 0.35 mW / cm2. The current density was measured in a Forward Scan (FS), during which the voltage across the solar cell 2 was increased from zero to the open-circuit voltage. From the measured current density and the applied voltage, a power conversion efficiency of about 1.4% was determined. The open-circuit voltage was determined as about 0.5 V and the short-circuit current density was determined as about 0.02 mA / cm2. The fill factor was determined as about 49%. As such, the solar cell 2 shown in Figure 3 can be considered as converting the absorbed portion of light into electrical power under indoor and one Sun illumination conditions. Figure 4C shows a graph of a measured current density in dependency on time for a constant voltage applied to the solar cell 2 shown in Figure 3. The graph shown in Figure 4C may be considered as showing the steady-state power conversion efficiency under one sun illumination of the solar cell 2. In this example, the voltage was held constant at about 0.6 V. The steady state power conversion efficiency was determined as about 1.4%.

[0104] Figure 4D shows another graph of a measured current density in dependency on time for a constant voltage applied to the solar cell 2 shown in Figure 3. The graph show in Figure 4D may be considered as showing the steady-state power conversion efficiency under indoor illumination of the solar cell 2 by the white light emitting diode. In this example, the voltage was held constant at about 0.5 V. The steady state power conversion efficiency was determined as about 2.9%.

[0105] The power conversion efficiency and steady state power conversion efficiency determined under indoor illumination of the solar cell is higher than the power conversion efficiency and the steady state power conversion efficiency determined under one Sun illumination. This may be due to indoor illumination having a different spectrum compared to the one Sun illumination. For example, the indoor illumination spectrum has only wavelengths in the visible spectral emission, which match an absorption spectrum of the active layer. As such, losses, for example due to nonabsorption and / or thermalisation may be reduced under indoor illumination compared to one Sun illumination.

[0106] Figure 5 schematically shows another exemplary solar cell 2. The solar cell 2 shown in Figure 5 is similar to that shown in Figure 3. As such, any features described in relation to the solar cell 2 shown in Figure 3 may also apply to the solar cell 2 shown in Figure 5. Only differences will be described in the following.

[0107] In this embodiment, the solar cell 2 comprises a rigid substrate 4. For example, the substrate may comprise a glass material, such as soda lime glass, borosilicate glass or the like. However, it will be appreciated that in other embodiments, the solar cell may comprise a flexible substrate. For example, the flexible substrate may comprise the layer of polymer material, e.g. the layer of plastic material, as described above.

[0108] The first electrode 8 may be formed or arranged on the substrate 4. Expressed differently, in this embodiment, the substrate 4 does not comprise an interlayer. The solar cell 2 shown in Figure 5 may be provided for use in an loT device, a wearable device or another device. When the solar cell 2 is used in a wearable device, e.g. outdoors, it may be necessary to encapsulate the solar cell 2, e.g. to protect the solar cell 2 against mechanical stress or impacts.

[0109] Figure 6A shows a graph of a measured current density in dependency on a voltage applied to the solar cell 2 shown in Figure 5. The current density was measured under one sun illumination (AM 1.5G, 100 mW / cm2) of the solar cell 2. The current density was measured in a Forward Scan (FS) and a Reverse Scan (RS), as described above.

[0110] From the measured current density and the applied voltage, the power conversion efficiency was determined as about 7 % in the Forward Scan and as about 11 % in the Reverse Scan. The open-circuit voltage was determined as about 1 V in the Forward and Reverse Scans. The short-circuit current density was determined as about 18 mA / cm2in the Forward Scan and as about 14 mA / cm2in the Reverse Scan. The fill factor was determined as about 40% in the Forward Scan and as about 77% in the Reverse Scan.

[0111] The power conversion efficiency, open-circuit voltage and short-circuit current density of the exemplary solar cell 2 shown in Figure 5 are increased relative to the power conversion efficiency, open-circuit voltage and short-circuit current density of the exemplary solar cell 2 shown in Figure 1. This may be due to the increase in the built-in electric field described above. As such, by selecting the conductive material of the first electrode 8 such that the work function of the first electrode 8 and the work function of the second electrode 10 is different, the performance of the solar cell 2 may be improved.

[0112] Figure 6B shows another graph of a measured current density in dependency on a voltage applied to the solar cell 2 shown in Figure 5. The current density was measured under indoor illumination of the solar cell 2 by a white light emitting diode using an irradiance of 0.35 mW / cm2. From the measured current density and the applied voltage, the power conversion efficiency was determined as about 11% in the Forward Scan and as about 20% in the Reverse Scan. The open-circuit voltage was determined as about 0.8 V in the Forward and Reverse Scans.

[0113] The short-circuit current density was determined as about 0.14 mA / cm2in the Forward and Reverse Scans. The fill factor was determined as about 32% in the Froward Scan and as about 59% in the Reverse Scan. As such, the solar cell 2 shown in Figure 5 can be considered as converting the absorbed portion of light into electrical power under indoor and one Sun illumination conditions. Figure 6C shows another graph of a measured current density in dependency on time for a constant voltage applied to the solar cell 2 shown in Figure 5. The graph show in Figure 6C may be considered as showing the steady-state power conversion efficiency under one sun illumination of the solar cell 2. In this example, the voltage was held constant at about 0.7V. The steady state power conversion efficiency was determined as about 3.4%.

[0114] Figure 6D shows another graph of a measured current density in dependency on time for a constant voltage applied to the solar cell 2 shown in Figure 5. The graph show in Figure 6D may be considered as showing the steady-state power conversion efficiency under indoor illumination by the white light emitting diode. In this example, the voltage was held constant at about 0.6 V. The steady state power conversion efficiency was determined as about 15%. The power conversion efficiency and steady state power conversion efficiency determined under indoor illumination is higher than the power conversion efficiency and steady state power conversion efficiency determined under one Sun illumination. As described above, this may be due to indoor illumination having a different spectrum compared to the one Sun illumination. For example, the indoor illumination spectrum has only wavelengths in the visible spectral emission. As such, losses, for example due to non-absorption and / or thermalisation may be reduced under indoor illumination compared to one Sun illumination.

[0115] Figures 7A and 7B each schematically show another exemplary solar cell 2. The solar cell 2 shown in Figure 7A is similar to that shown in Figure 3. As such, any features described in relation to the solar cell 2 shown in Figure 3 may also apply to the solar cell 2 shown in Figure 7A. The solar cell 2 shown in Figure 7B is similar to that shown in Figure 5. As such, any features described in relation to the solar cell 2 shown in Figure 5 may also apply to the solar cell 2 shown in Figure 7B. Only differences will be described in the following.

[0116] The solar cell 2 shown in each of Figures 7A and 7B comprises an organic solar cell (OSC) or plastic solar cell. The active layer 6 comprises a polymer material. The polymer material may comprise poly(3-hexylthiophene): [6,6]-phenyl C61 -butyric acid methylester (P3HT: PCBM) or poly(3-hexylthiophene): indene-C60 bisadduct (P3HT: ICBA), a combination of PM6: Y6 and PM6: F-2CI, PBDB-T-2F:BTP-4F-BTP-M, PBODT:PC71 BM:ITIC and / or another polymer material. PM6 is a derivative of PBDB- T-2. A thickness of the active layer 6 may be between about 100 nm and about 900 nm. The thickness of the active layer 6 may be between about 400 nm and 900 nm, such as about 500 nm or about 800 nm, e.g. to decrease or avoid a roughness of the active layer 6, which may be due to the layer 4a of textile material. The polymer material of the active layer 6 may selected such that the solar cell 2 achieves a desired power conversion efficiency, e.g. when the active layer 6 has a thickness between about 400 nm and about 900 nm, e.g. about 500 nm or about 800 nm. For example, the selected polymer material of the active layer 6 may comprise PBDB-T-2F:BTP-4F- BTP-M, PBODT:PC71 BM:ITIC and / or the like. The polymer material of the active layer 6 may be configured such that the bandgap of the polymer material is between about 1.5 eV and about 2.3 eV, such as about 1.56 eV.

[0117] It will be appreciated that when the solar cell 2 comprises another substrate, such as a flexible substrate comprising the layer of polymer material or the rigid substrate comprising the glass material, the thickness of the active layer 6 may be less than about 400 nm. For example, in the embodiment shown in Figure 7B, the thickness of the active layer 6 may be between about 100 nm and about 400 nm, such as between about 100 nm and 300 nm.

[0118] In the embodiments shown in Figures 7A and 7B, the solar cell 2 may comprise no hole transport layer 14. The second electrode 10 may be arranged or formed on the active layer 6. The second electrode 10 may be configured to provide the a hole transport layer. For example, the hole transport layer may be part of the dielectric- metal-dielectric transparent electrode.

[0119] In the embodiment shown in Figures 7A and 7B, the electron transport layer 12 comprises an oxide material, such as zinc oxide (ZnO). However, it will be appreciated that in other embodiments another oxide material, such as one or more of the oxide materials described above, may be used for the electron transport layer.

[0120] Figure 8 shows a flow chart illustrating in overview a method 100 of manufacturing a solar cell. The solar cell manufactured using the method 100 may comprise any of the features of any of the solar cells 2 described above.

[0121] In step 105, the method 100 comprises providing a substrate 4.

[0122] In step 110, the method 100 comprises forming a first electrode 8. The first electrode 8 may be formed on the substrate 4, e.g. using a deposition process, such as a thermal evaporation process, a blade coating process or another deposition process. The step of forming the first electrode 8 may comprise depositing one or more layers of a conductive material on the substrate 4. For example, a first layer 8a of a first conductive material may be deposited on the substrate 4. A second layer 8b of a second conductive material may be deposited on the first layer 8a of the first conductive material, e.g. to form the first electrode 8 of the solar cell 2 shown in Figure 1. Alternatively, only a single layer of conductive material may be deposited on the substrate 4 to form the first electrode 8, e.g. to form the first electrode 8 of the solar cell 2 shown in Figures 3, 5, 7A, 7B or 10. By forming the first electrode from a conductive material, such as aluminium, described herein and using a deposition process, such as the thermal evaporation process, a wettability of a material of the electron transport layer 12 may be improved.

[0123] In embodiments where the conductive material of the first electrode comprises the carbon material, the method comprises using a blade coating process to deposit a precursor carbon material on the substrate 4. This process may allow for a scalable formation of the first electrode 8, e.g. the solar cell 2. The blade coating process comprises depositing the precursor carbon material on the substrate 4. The precursor carbon material may be provided in the form of a carbon paste. The carbon paste may comprise a conductive graphite powder, graphene, such as graphene flakes, carbon nanotubes and / or any other suitable conductive carbon material. The carbon paste may also comprise a pasting solution or liquid. The carbon paste may comprise a carbon paste prepared by Dycotec or Dyenamo. However, it will be appreciated that in other embodiments any other suitable carbon paste may be used. The blade coating process comprises moving or passing a blade 10 over the substrate 4, e.g. to spread the precursor carbon material evenly across a surface of the substrate 4. A speed of the blade may be between about 1 mm / s and 30 mm / s such as about 10 mm / s. The blade coating process may be performed in an ambient air environment.

[0124] Subsequent to depositing the precursor carbon material on the substrate 4, the carbon material may be annealed at a temperature between 70°C and 100°C, such as about 80°C for a duration of time. For example, the duration of time may be about 10 minutes. However, it will be appreciated that in other embodiments, the duration of time may be longer or shorter than 10 minutes. This may form a layer of carbon material on the substrate. The use of the carbon material as a conductive material of the first electrode 8 may allow for at least the first electrode 8 to be formed at a decreased temperature and / or a decreased sheet resistance. For example, a sheet resistance of the first electrode 8 may be in the range of about 30 Ohms to about 40 Ohms. Additionally or alternatively, the use of the carbon material as a conductive material of the first electrode 8 may decrease costs for manufacturing the solar cell and / or may allow for the use of large-area processes for manufacturing the solar cell.

[0125] In embodiments where the conductive material of the first electrode comprises the carbon material, the method may comprise forming a further layer on the conductive material. For example, in some embodiments, the method may comprise depositing a metal material, such as aluminium, on the carbon material, e.g. using the deposition process mentioned above. In such embodiments, the conductive material comprising the carbon material may define a first layer of a first conductive material. The further layer may define a second layer of a second conductive material.

[0126] In some embodiments, the further layer may comprise a polymer material, such as polyethylenimine(PEI) or the like. The further layer may be formed by depositing the polymer material on the carbon material using a deposition process, such as spin coating.

[0127] As will be described below, in some embodiments, the conductive material of the first electrode 8 comprises a transparent conducting oxide, such as indium tin oxide (ITO). In such embodiments, the first electrode 8 is configured transparent to the portion of light to be absorbed by the active layer 6. It will be appreciated that in other embodiments another transparent conducting material may be used, such as fluorine doped tin oxide (FTO), niobium doped anatase titanium dioxide (NTO), doped zinc oxide or any other suitable transparent conducting material. The first electrode may be formed using a deposition process, such as a sputtering process, a physical vapour deposition process or any other suitable deposition process.

[0128] The method 100 may comprise pre-processing the substrate 4. The step of preprocessing the substrate 4 may comprise using a material removal process, e.g. to remove any organic matter from the substrate 4. The material removal process may comprise an ashing process, such as a plasma ashing process. This may allow for an increased wettability of the first layer 8a of the first conductive material, the second layer 8b of the second conductive material and / or the single layer of conductive material on the substrate 4.

[0129] Subsequent to forming the first electrode 8, the method 100 may comprise forming an electron transport layer 12. The electron transport layer 12 may be formed or deposited on the first electrode 8 using a deposition process, such as a spin coating process, a sputtering process, electron beam deposition, a blade coating process or another deposition process.

[0130] The method 100 may additionally comprise pre-processing of the first electrode 8. Pre-processing of the first electrode 8 may comprise using a material removal process, e.g. to remove any organic matter from the first electrode 8. The material removal process may comprise an ashing process, such as a plasma ashing process. This may allow for an increased wettability of the material of the electron transport layer 12 on the first electrode 8.

[0131] In step 115, the method 100 comprises forming an active layer 6. As described above, the active layer 6 is configured to absorb at least the portion of light and to convert the absorbed portion of light into a plurality of charge carriers. The method may comprise forming a precursor solution or mixture. In this embodiment, the precursor solution or mixture may comprise one or more organic solvents, such as dimethylformamide, an organic halide, such as methylammonium iodide, and a crystalline compound, such as lead acetate or the like. The use of the lead acetate may avoid the use of antisolvent. It has been found that the use of antisolvent may lead to a decreased performance of the solar cell 2, e.g. when the substrate comprises the layer of textile material and no interlayer. For example, the antisolvent may soak into the layer of textile material. The precursor solution or mixture may comprise about 353 mg of methylammonium iodide, 277.5 mg of lead acetate and 1 ml of dimethylformamide. Once the precursor solution or mixture is dissolved, aggregated active layer material is removed from the dissolved precursor solution, e.g. by filtering. The active layer material may be deposited on the electron hole layer 12, e.g. using a deposition process, such as a spin coating process or another deposition process. It will be appreciated that the active layer may be formed to comprise a different perovskite material.

[0132] The active layer 6 of the solar cells 2 shown in Figures 7A and 7B may be formed by using one or more of the processes described above. However, the precursor solution or mixture may comprise one or more components of the exemplary polymer materials described herein.

[0133] Subsequent to forming the active layer 6, the method 100 may comprise forming a hole transport layer 14. The hole transport layer 14 may be formed or deposited on the active layer 6 using a filtering process and / or a deposition process, such as a spin coating process or another deposition process. For example, an organic compound, such as Spiro-MeOTAD (CsiHesl^UOs) or the like, may be provided in a solution. The method may comprise filtering aggregates of the organic compound from the solution and depositing the organic compound on the active layer 6.

[0134] Subsequent to forming the hole transport layer 14, the method may comprise an oxidation and / or doping step. This may allow for the formation of an oxidised and / or doped hole transport layer 14. For example, subsequent to forming the hole transport layer 14, the solar cell may be stored in an environment comprising oxygen. For example, the environment may comprise dry air.

[0135] In step 120, the method 100 comprises forming a second electrode 10. The second electrode 10 may be formed on the hole transport layer 14. The step of forming the second electrode 10 may comprise depositing a plurality of layers of material on the hole transport layer 14, e.g. using a deposition process, such as a thermal evaporation process or another deposition process. For example, a first layer 10a of semiconductor material may be formed or deposited on the hole transport layer 14. As described above, the semiconductor material may comprise molybdenum oxide (MoOx) or the like. A second layer 10b of conductive material may be formed or deposited on the first layer 10a of semiconductor material. The conductive material of the second layer 10b may comprise a metal material or a transition metal material, such as gold or the like. A third layer 10c of conductive material 10c may be formed or deposited on the second layer 10b of conductive material. The conductive material of the third layer 10c may comprise a metal material or a transition metal material, such as silver or the like. A fourth layer 10d of semiconductor material may be formed or deposited on the third layer 10c of conductive material. As described above, the semiconductor material of the first and fourth layers 10a, 10d may be the same. It will be appreciated that in other embodiments, a dielectric material may be used as an alternative to the semiconductor material, as described above, and / or more or less than four layers of conductive material may be formed or deposited on the hole transport layer.

[0136] In some embodiments, the conductive material of the second electrode 10 comprises the carbon material. In such embodiments, the second electrode may be formed on the hole transport layer as described above in relation to the first electrode. In such embodiments, the second electrode may comprise any of the features of the first electrode.

[0137] It will be appreciated that in embodiments where the active layer 6 of the solar cell 2 comprises the polymer material, the method 100 may comprise forming the second electrode 10 on the active layer 6. Expressed differently, no separate hole transport layer other than that provided by the second electrode 10, as described above, may be present, when the active layer 6 of the solar cell 2 comprises the polymer material.

[0138] The method 100 may comprise one or more annealing steps. For example, the method 100 may comprise annealing of the electron transport layer 12. An annealing duration and / or annealing temperature may be selected based on one or more materials of the substrate 4. For example, the annealing duration and / or annealing temperature may be selected to be compatible with the materials of the substrate 4. In embodiments, where the substrate 4 comprises the layer 4a of textile material, the annealing duration may be selected to be around 20 minutes and / or the annealing temperature may be selected to be about 120°C.

[0139] The annealing steps may comprise annealing of the active layer 6. An annealing duration may be about 5 minutes and / or an annealing temperature may be about 100°C. The active layer may be annealed under vacuum conditions, e.g. a pressure of about 0.1 mbar (10 Pa), for some or all of the annealing duration.

[0140] The method may comprise one or more ultraviolet (UV)-ozone treatment steps. For example, the electron transport layer 12 may be exposed to UV-ozone for a selected duration. This may increase a wettability of the active layer material on the electron transport layer 12 and / or reduce or remove one or more surface defects from a surface of the electron transport layer 12. In this embodiment, a duration of the UV- ozone treatment may be selected to be around 10 minutes. The method describes the formation of a solar cell defining an n-i-p structure. It will be appreciated that in other embodiments, the order of one or more steps of the steps may be different in other embodiments. For example, in embodiments where the solar cell defines a p-i-n structure, a hole transport layer may be formed between the first electrode and the active layer. In such embodiments, an electron transport layer may be formed between the active layer and the second electrode. However, it will be appreciated that in some embodiments, the solar cell may not comprise a hole transport layer, as described herein.

[0141] Figure 9A schematically shows an exemplary wearable device 16 comprising the solar cell 2. The solar cell 2 may be integrated or comprised in the wearable to device 12 to generate electricity for the wearable solar cell 2. In this embodiment, the wearable device 16 comprises a watch or smartwatch. However, it will be appreciated that in other embodiments, the wearable device may comprise a sensor, an activity tracker, a medical device or another wearable device.

[0142] Figure 9B schematically shows an exemplary loT (Internet of Things) device 18 comprising the solar cell 2. The loT device 18 may be considered as a device that is configured to connect, e.g. wirelessly connect, to a network, e.g. to transmit data to and / or from the network. The network may comprise other devices, such as other loT devices. In this embodiment, the loT device 18 may comprise a sensor, an actuator, a communication device, a medical device or another loT device. The loT device may be configured for indoor use.

[0143] In this embodiment, the solar cell 2 is integrated into the loT device 18 to provide generate electricity for the loT device 18. However, it will be appreciated that in other embodiments, the solar cell may be provided separately and / or remotely from the loT device. In some embodiments, the loT device may comprise the wearable device.

[0144] Figure 9C schematically shows an item of furnishing 20 comprising the solar cell 2. The solar cell 2 may be integrated into the item of furnishing 20 to generate and / or provide electricity to another device, such as the loT device 18. The item of furnishing may comprise an item of furniture, a decorative item or another item of furnishing. For example, the item of furniture may comprise at least one of: a bed, a chair, a table, seat arm chair or other item of furniture. The decorative item may comprise at least one of a cover for a window, such as a curtain, a blind or other window cover, a wall hanging item, such as a tapestry, a picture, or another decorative object or item.

[0145] In the embodiment shown in Figure 9C, the item of furnishing 20 comprises a cover for a window 22, such as a blind. The solar cell 2 may configured to have a surface area similar or the same as a surface area of the item of furnishing. This may allow for an amount of electricity generated by the solar cell 2 to be increased.

[0146] It will be appreciated that the use of the solar cell disclosed herein is not limited to the exemplary uses and / or applications described herein.

[0147] It will be appreciated that the wearable device 16, the loT device 18 and / or the item of furnishing 20 may comprise more than one solar cell 2. One or more solar cells 2 may be part of a solar panel (not shown for sake of clarity). The solar panel may comprise one or more further electric components, electric circuits, electric devices or the like. The solar panel may be integrated in the wearable device 16, the loT device 18, the item of furnishing 20 and / or another device or item.

[0148] Figure 10 schematically shows another exemplary solar cell 2. The solar cell 2 shown in Figure 10 is similar to that shown in Figure 5. As such, any features described in relation to the solar cell 2 shown in Figure 5 may also apply to the solar cell 2 shown in Figure 10. Only differences will be described in the following.

[0149] In this embodiment, the solar cell 2 comprises a rigid substrate 4. For example, the substrate may comprise a glass material, such as soda lime glass, borosilicate glass or the like. The first electrode 8 is formed or arranged on the substrate 4. In this embodiment, the first electrode 8 comprises a transparent conducting material, such as a transparent conducting oxide. The transparent conducting material comprises indium tin oxide (ITO). However, it will be appreciated that in other embodiments another transparent conducting material may be used, such as fluorine doped tin oxide (FTO), niobium doped anatase titanium dioxide (NTO), doped zinc oxide or any other suitable transparent conducting material. A thickness of the first electrode may be between about 50 nm and 200 nm, such as about 110 nm. In this embodiment, the first electrode 8 is configured to be transparent to the portion of light to be absorbed by the active layer 6.

[0150] In this embodiment, the second electrode 10 comprises the carbon material. A thickness of the second electrode 10 may be between about 10 pm and 20 pm, such as about 15 pm. The solar cell 2 shown in Figure 10 may be configured for bottom illumination.

[0151] As described above, the solar cell 2 is configured such that a work function of the first electrode is different from a work function of the second electrode.

[0152] The conductive material of the first electrode 8 may be selected or configured such that the work function of the first electrode 8 is different, e.g. lower, than the work function of the second electrode 10. For example, indium tin oxide has a work function of about 4.5 eV to 4.8 eV. The second electrode 10 comprises the carbon material, which has a work function of about 5.1 eV. These exemplary values of the work functions described above correspond to the work function values of the individual materials of the first and second electrodes 8, 10. As described above, the work function of each of the first and second electrode 8, 10 may be different, when these materials are part of the solar cell 2. For example, the work function of the first electrode 8 may be decreased to about 4 eV due to the presence of the electron transport layer 12. For example, when the electron transport layer comprises tin oxide (SnC>2), the work function of the first electrode 8 may be the same as the work function of tin oxide. The work function of the second electrode may be the same or similar to the work function of the hole transport layer 14. For example, when the hole transport layer comprises Spiro-MeOTAD or CuSCN, the work function of the hole transport layer is about 5.2 eV to 5.3 eV. In the embodiment shown in Figure 10, the hole transport layer 14 comprises CuSCN. A thickness of the hole transport layer 14 comprises about 40. Figure 11A shows a graph of a measured current density in dependency on a voltage applied to the solar cell 2 shown in Figure 10. The current density was measured under one sun illumination (AM 1.5G, 100 mW / cm2) of the solar cell 2. The current density was measured in a Forward Scan (FS) and a Reverse Scan (RS), as described above.

[0153] From the measured current density and the applied voltage, the power conversion efficiency was determined as about 9.6 % in the Forward Scan and as about 10 % in the Reverse Scan. The open-circuit voltage was determined as about 0.9 V in the Forward and Reverse Scans. The short-circuit current density was determined as about -20 mA / cm2in the Forward and Reverse Scans. The fill factor was determined as about 53% in the Forward Scan and as about 54% in the Reverse Scan.

[0154] The power conversion efficiency, open-circuit voltage and short-circuit current density of the exemplary solar cell 2 shown in Figure 10 are increased relative to the power conversion efficiency, open-circuit voltage and short-circuit current density of the exemplary solar cell 2 shown in Figure 1. This may be due to the increase in the built-in electric field described above. As such, by configuring the solar cell 2 such that the work function of the first electrode 8 and the work function of the second electrode 10 is different, the performance of the solar cell 2 may be improved.

[0155] Figure 11B shows another graph of a measured current density in dependency on a voltage applied to the solar cell 2 shown in Figure 10. The current density was measured under indoor illumination of the solar cell 2 by a white light emitting diode using an irradiance of 0.32 mW / cm2. From the measured current density and the applied voltage, the power conversion efficiency was determined as about 12% in the Forward Scan and as about 16% in the Reverse Scan. The open-circuit voltage was determined as about 0.7 V in the Forward Scan and as about 0.8 V in the Reverse Scan.

[0156] The short-circuit current density was determined as about -0.12 mA / cm2in the Forward and Reverse Scans. The fill factor was determined as about 45% in the Froward Scan and as about 51% in the Reverse Scan. As such, the solar cell 2 shown in Figure 10 can be considered as converting the absorbed portion of light into electrical power under indoor and one Sun illumination conditions.

[0157] The exemplary solar cells described herein may each be considered as comprising a monolithic structure. For example, each solar cell described herein may be formed altogether on a single substrate, as described above. The terms “carbon material” may be interchangeably used with the term “carbon”.

[0158] Although the disclosure has been described in terms of embodiments as set forth above, it should be understood that these embodiments are illustrative only and that the claims are not limited to those embodiments. Those skilled in the art will be able to make modifications and alternatives in view of the disclosure which are contemplated as falling within the scope of the appended claims. Each feature disclosed or illustrated in the present specification may be incorporated in the disclosure, whether alone or in any appropriate combination with any other feature disclosed or illustrated herein.

Claims

CLAIMS:

1. A solar cell comprising: a substrate; an active layer comprising a perovskite material or a polymer material, the active layer being configured to absorb at least a portion of light incident on the solar cell and to convert the absorbed portion of light into a plurality of charge carriers; a first electrode configured to be opaque and / or to reflect light transmitted through the active layer towards the active layer; and a second electrode configured to be transparent to the portion of light to be absorbed by the active layer; wherein the active layer is arranged between the first and second electrodes and the first electrode is arranged between the substrate and the active layer, and wherein the solar cell is configured such that a work function of the first electrode is different from a work function of the second electrode.

2. The solar cell of claim 1 , wherein the solar cell is configured such that the work function of at least one of the first and second electrodes is lower than the work function of at least one other of the first and second electrodes.

3. The solar cell of claim 1 or 2, wherein the substrate comprises a rigid substrate.

4. The solar cell of claim 1 or 2, wherein the substrate comprises a flexible substrate.

5. The solar cell of claim 4, wherein the flexible substrate comprises a layer of textile material or a layer of polymer material.

6. The solar cell of any preceding claim, wherein the first electrode comprises a conductive material.

7. The solar cell of claim 6, wherein the second electrode comprises a conductive material that is different from the conductive material of the first electrode.

8. The solar cell of claim 6 or 7, wherein the first electrode comprises a single layer of the conductive material or the first electrode comprises a plurality of layers, at least one of the plurality of layers comprising the conductive material.

9. The solar cell of any one of claims 6 to 8, wherein the conductive material comprises at least one of a metal, a transition metal and a carbon material.

10. The solar cell of any preceding claim, wherein the second electrode is configured as a dielectric-metal-dielectric transparent electrode.

11. The solar cell of any preceding claim, wherein the solar cell comprises an electron transport layer arranged between the first electrode and the active layer12. The solar cell of any preceding claim, wherein the solar cell comprises a hole transport layer arranged between the active layer and the second electrode.

13. The solar cell of any preceding claim, wherein the perovskite material or polymer material is configured such that a bandgap of the perovskite material or polymer material is between about 1.5 eV and about 2.3 eV.

14. A method of manufacturing a solar cell, the method comprising: providing a substrate; forming a first electrode; forming an active layer comprising a perovskite material or a polymer material, the active layer being configured to absorb at least a portion of light incident on the solar cell and to convert the absorbed portion of light into a plurality of charge carriers; and forming a second electrode, the second electrode being configured to be transparent to the portion of light to be absorbed by the active layer and the first electrode being configured to be opaque and / or to reflect light transmitted through the active layer towards the active layer, wherein the active layer is formed between the first and second electrodes and the first electrode is formed between the substrate and the active layer, and wherein the solar cell is configured such that a work function of the first electrode is different from a work function of the second electrode.

15. The method of claim 14, wherein the substrate comprises a rigid substrate or a flexible substrate.

16. The method of claim 15, wherein the flexible substrate comprises a layer of textile material or a layer of polymer material.

17. The method of any one of claims 14 to 16, wherein the first electrode is formed as a single layer of a conductive material or the first electrode comprises a plurality of layers at least one of the plurality of layers comprising the conductive material.

18. An loT (Internet of Things) and / or wearable device comprising a solar cell according to any one of claims 1 to 13.

19. An item of furnishing comprising a solar cell according to any one of claims 1 to

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