TECHNOLOGY FOCUS - CHEMICAL ENGINEERING - Preferred Heterojunction: The heterojunction is sensitized by at least one sensitizing agent. The functionalized electron acceptor moieties comprise at least one 2-dimensional or 3-dimensional network of carbon atoms, optionally including up to 10% of heteroatoms, functionalized by at least one organic group having affinity for the n-type material surface. The 2-dimensional or 3-dimensional networks of carbon atoms are selected from single-layer graphene, graphene having two, three, four or five layers, carbon nanotubes, and fullerenes, all optionally doped with up to 10% of at least one heteroatom selected from oxygen, boron, sulfur and nitrogen, preferably C60 or C70 fullerenes. The organic group having affinity for the n-type material surface is at least one group selected from an organic acid and an organic thio-acid. The surface of the n-type layer is functionalized with at least a partial mixed monolayer of at least one functionalized electron acceptor and at least one sensitizing agent. The pore-filling-fraction of the porous layer of n-type material by the organic p-type material is no more than 50%. The sensitizing agent comprises at least one dye selected from a ruthenium complex dye, a metal-phalocianine complex dye, a metal-porphryin complex dye, a squarine dye, a thiophene based dye, a fluorine based dye, a polymer dye, and mixtures. The sensitizing agent comprises at least one inorganic light absorbing thin film or semiconductor nanoparticle layer formed from a material selected from lead sulfide (PbS), lead selenide (PbSe), tin sulfide (SnS), tin selenide (SnSe), antimony sulfide (SbS), antimony selenide (SbSe), cadmium selenide (CdSe), germanium (Ge), and silicon (Si). The heterojunction comprises at least one ionic additive, where the ionic additive is a lithium salt such as lithium bis(trifluoromethylsulfonyl)imide salt (Li-TFSI) or Li perchlorate. The ionic additive is a mixture of a metal salt and an ionic liquid. The ionic additive comprises or consists of an ionic liquid, selected from 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, 1-allyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, 1,3-dihydroxy-2-methylimidazolium bis(trifluoromethylsulfonyl)imide, 1,3-dimethoxy-2-methylimidazolium bis(trifluoromethylsulfonyl)imide and mixtures. The p-type material is an organic polymer selected from polythiophenes, poly p-phenylene vinylenes, mixtures, derivatives and copolymers, most preferably poly(2,1,3-benzothiadiazole-4,7-diyl(4,4-bis(2-ethylhexyl)-4H-cyclopenta(2,1-b:3, 4-b')dithiophene-2,6-diyl)) (PCPDTBT). The p-type material is an organic polymer having a molecular weight (Mn) of greater than 15,000. The p-type material is substantially electrically continuous throughout the mesoporous film. The n-type semiconductor material comprises at least one single metal oxide, compound metal oxide, doped metal oxide, carbonate, sulfide, selenide, telluride, nitrides and/or multi-compound semiconductor, most preferably titanium dioxide (TiO2), tin dioxide (SnO2) or zinc oxide (ZnO). The n-type material has a surface area of 1-1000 m2/g and preferably in the form of an electrically continuous layer. The n-type material has a thickness of 0.05-30 mu m, preferably 2-3 mu m. The n-type material is selected from oxides of titanium (Ti), zinc (Zn), tin (Sn), tungsten (W) and mixtures, and where the n-type material is optionally surface coated. Preferred Device: The optoelectronic device is a solar cell, phototransistor or photo-detector, preferably a solid state dye sensitized solar cell and/or solid state polymer sensitized solar cell. The device is encapsulated so as to be substantially isolated from atmospheric oxygen. Preferred Method: In manufacturing the solid-state p-n heterojunction comprising the organic p-type material in contact with the porous layer of n-type material, optional step (d) is included and comprises treating the compact layer and/or the porous layer of n-type material with a mixture of at least two ionic materials. The ionic materials comprise at least one metal salt, preferably at least one lithium salt, and at least one ionic liquid, preferably 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide. Step (d) takes place and comprises contacting the porous layer of n-type material with a solution of Li-TFSI.