[0030] The electrode and PEIE layers may be respectively deposited onto a surface of any substrate that is or can be exposed to sunlight, such as, for example, buildings, vehicles, modular panels, photovoltaic device substrates, and the like. The spray coating techniques used in the processes according to the present invention enable the production of photovoltaic coating systems comprising a stack of spray coated layers, including an electrode layer and a PEIE layer, that together form a functional photovoltaic system deposited onto any convenient or suitable substrate. The substrate may, for example, comprise an electrically insulating dielectric layer that may be deposited onto an underlying substrate material to provide a homogenous and continuous base layer that is electrically, chemically, and mechanically inert to the overlying functional photovoltaic layers. The dielectric layer may provide a non- porous and relatively planar base layer. Typically the dielectric base layer, if present, has a surface roughness of less than 25 nanometers (Ra), preferably of less than 20 nanometers (Ra), more preferably of less than 15 nanometers (Ra), even more preferably of less than 10 nanometers (Ra), or less than 5 nanometers (Ra).
[0031 ] Such optionally present inert, non-porous, and relatively planar dielectric layer may, for example, comprise a cured acrylic urethane clear-coat layer. As used herein the term "cured," refers to the condition of a liquid coating
composition in which a film or layer formed from the liquid coating composition is at least tack free to touch. As used herein, the terms "cure" and "curing" refer to the progression of a liquid coating composition from the liquid state to a cured state and encompass physical drying of coating compositions through solvent or carrier evaporation (e.g., thermoplastic coating compositions) and/or chemical crosslinking of components in the coating compositions (e.g., thermosetting coating compositions). An example of a suitable acrylic urethane clear-coating composition that may be used to form a dielectric layer on a substrate is the D8109 UHS Clearcoat available from PPG Industries, Inc. As an example, an epoxy primer composition may be used to form an epoxy primer layer on a substrate, and an acrylic urethane clear-coating composition may be used to form a dielectric layer deposited on the underlying epoxy primer layer. According to the present invention, a dielectric layer may be spray coated onto a substrate, and the electrode and PEIE layers may be respectively spray coated onto the dielectric layer. A spray coated dielectric layer may have any dry film thickness, provided the dielectric layer provides a base layer with sufficiently low surface roughness (less than 25 nanometer Ra, for example).
[0032] The processes for producing low work function electrodes described in this specification may be incorporated into processes for producing photovoltaic systems. Figure 1 illustrates a process 10 for producing a photovoltaic system in accordance with the present invention. A substrate is provided at step 12. The substrate may comprise any substrate that is or can be exposed to sunlight, such as, for example, buildings, vehicles, modular panels, photovoltaic device substrates, and the like. A dielectric layer is then deposited onto the substrate at step 14. The dielectric layer may comprise a spray coated layer, as described above. For example, the dielectric layer may comprise a spray coated layer comprising a cured acrylic urethane clear-coat or a combination of an underlying epoxy primer layer and an overlying acrylic urethane clear-coat layer. A first electrode layer is subsequently deposited onto the dielectric layer at step 16. The first electrode layer may comprise a spray coated layer, as described above. For example, the first electrode layer may comprise a spray coated PEDOT:PSS PH1000 layer, a spray coated silver layer formed from the reaction products of a Tollens' reaction, or a spray coated layer of dielectric material comprising metallic particles embedded in the dielectric material. A PEIE layer is deposited onto the first electrode layer at step 20. The PEIE layer can be spray coated onto the first electrode layer, as described above.
[0033] A bulk heterojunction active layer is then deposited onto the PEIE layer at step 22 of the process illustrated in Figure 1. The bulk heterojunction active layer may comprise an organic, semiconducting, low band gap polymer that functions as an electron donor when contacted with visible light. Typically the bulk
heterojunction active layer comprises a blend comprising an organic, semiconducting, low band gap polymer and an electron acceptor compound. For example, the bulk heterojunction active layer may comprise a blend of poly(3-hexyl thiophene) and [6,6]-phenyl C6i-butyric acid methyl ester (P3HT:PCBM). Other low band gap polymers suitable for the bulk heterojunction active layer include, for