TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Components: The first electrode layer comprises indium tin oxide. The zinc acetate in the coating ink of step (bi) is in the form of zinc acetate di-hydrate (Zn(OAc)2-2H2O). The coating ink of step (bi) further comprises diacetoxy(hydroxy)aluminum (AlOH(OAc)2), preferably 1-1.5 wt.%, compared with Zn(OAc)2-2H2O. The second electrode is a metal layer, preferably a silver layer. The metal layer is formed by coating an ink comprising metal flakes, water and a water-soluble binder on to the hole transport layer, preferably by screen printing, and drying the ink.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: The surface energy of the first electrode layer is treated, preferably by UV-ozone treatment, oxygen plasma treatment or corona treatment, in order to increase its surface energy, prior to carrying out step (b). The coating ink of step (bi) further comprises a wetting agent. The wetting agent is Zonyl FSO-100 (RTM: 2-(Perfluoroalkyl)ethanol, CAS No 65545-80-4) (preferred) or Triton X-100 (RTM: Polyethylene glycol p-(1,1,3,3-tetramethylbutyl)-phenyl ether, CAS No 9002-93-1). The level of wetting agent in the ink is Zonyl FSO-100 (RTM: 2-(Perfluoroalkyl)ethanol, CAS No 65545-80-4) (0.5-7.5 wt.%, preferably 1-3 wt.%) compared with Zn(OAc)2.2H2O, or Triton X-100 (RTM: Polyethylene glycol p-(1,1,3,3-tetramethylbutyl)-phenyl ether, CAS No 9002-93-1) (0.5-25 wt.%, preferably 9 wt.%) compared with Zn(OAc)2-2H2O. The coating ink of step (bi) has a composition of Zn(OAc)2-2H2O (0.1 gml-1 in water), AlOH(OAc)2 (1.5 wt.% compared with the Zn(OAc)2.2H2O) and Zonyl FSO-100 (RTM: 2-(Perfluoroalkyl)ethanol, CAS No 65545-80-4) (1-3 wt.% compared with the Zn(OAc)2.2H2O). The heating step (biii) is carried out at 140 degrees C for at least 5 minutes, preferably in the presence of humidity, and preferably for 10 minutes or longer. The ester groups are groups having a tertiary carbon alpha - to the ester oxygen and comprising a polyether moiety having one or more free hydroxy groups. The fullerene is phenyl-61C-butyric acid methyl ester, phenyl-71C-butyric acid methyl ester, bisindenofullerenes, and fullerene compound of formula (II). The coating ink for the hole transport layer in step (d), the active layer is wetted with an alcohol. The alcohol used to wet the active layer and in the coating ink in step (di) is isopropanol.    TECHNOLOGY FOCUS - POLYMERS - Preferred Components: The first electrode layer is a silver grid under a poly(3,4-ethylenedioxythiophene) (PEDOT):poly(styrenesulfonate) (PSS) layer. The step (ci) is used, and the light harvesting polymer is poly-3-hexylthiophene. The step (cii) is used and the soluble precursor of the light harvesting polymer is a polythiophene, or copolymer of thiophene with a benzothiadiazole, a thienopyrazine, a dithienothiophene or a thienothiophene, substituted with ester groups of formula (C=O-O-R) capable of being thermally cleaved to give free carboxylic acid groups. The soluble precursor to the light harvesting polymer is (2,2')bithiophenyl-4-carboxylic acid 3-(2,3-dihydroxy-propoxy)-1,1-dimethyl-propyl ester of formula (I). The hole transporting compound is PEDOT:PSS, PEDOT:PTS (p-toluene sulfonate), vapor phase deposited PEDOT, polyprodot, polyaniline, polypyrrole, vanadium pentoxide or molybdenum trioxide. Preferred Method: The treatment to convert the soluble precursor into the light harvesting polymer substantially insoluble in the solvent of the coating ink is thermal treatment to cleave the at least some of the ester groups to leave carboxylic acid groups. The thermal treatment is carried out at 100-300 degrees C, preferably 140 degrees C for at least 20 minutes, preferably 4 hours. The treatment to convert the soluble precursor into the light harvesting polymer substantially insoluble in the solvent of the coating ink is thermal treatment to cleave both the ester groups and the carboxylic acid groups, and the thermal treatment is carried out at around 300 degrees C. The thermal treatment is carried out using a laser or other high powered light source in the wavelength of 475-532 nm.R, n = not defined.