TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Method: In preparing the coating ink for forming the zinc oxide electron transport layer, the zinc acetate and the wetting agent are mixed in water, where the zinc acetate is used in the form Zn(OAc)2.2H2O. The wetting agent is Zonyl FSO-100 (2-(perfluoroalkyl)ethanol, CAS No 65545-80-4) or Triton X-100 (polyethylene glycol p-(1,1,3,3-tetramethylbutyl)-phenyl ether, CAS No 9002-93-1). The wetting agent is present in the ink in an amount of between 0.5 and 7.5 wt.% of Zonyl FSO-100 compared with Zn(OAc)2.2H2O, or between 0.5 and 25 wt.% of Triton X-100 compared with Zn(OAc)2.2H2O. The Zonyl FSO-100 is used in an amount of 1 to 3 wt.% compared with Zn(OAc)2.2H2O, or Triton X-100 is used in an amount of 9 wt.% compared with Zn(OAc)2.2H2O. The wetting agent is Zonyl FSO-100 (2-(perfluoroalkyl)ethanol, CAS No 65545-80-4). The method further comprises mixing aluminum hydroxide (AlOH)(OAc)2 into the ink and subsequently filtering out solids, where the AlOH(OAc)2 is added in an amount of between 0.5 and 6 wt.% compared with Zn(OAc)2.2H2O, preferably in an amount of 1 to 1.5 wt.%. In preparing the zinc oxide electron transporting layer, the heating step (c) is carried out at 140 degrees C for at least 5 minutes, where the heating is carried out in the presence of humidity. In preparing the organic photovoltaic device or the organic LED having the zinc oxide electron transport layer, the electrode layer comprises indium titanium oxide (ITO). Step (c) is carried out by applying a coating ink comprising a light-harvesting polymer and an electron acceptor to the electron transport layer, and drying the coating ink layer. The active layer comprises poly-3-hexylthiophene (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM). Step (c) is carried out by applying a coating ink comprising a soluble precursor of a light harvesting polymer, an electron acceptor and a solvent to the electron transport layer, drying the coating ink layer, and treating the dried coating ink layer to convert the soluble precursor into a light harvesting polymer that is substantially insoluble in the solvent of the coating ink. The coating ink in step (c) comprises a precursor of a light harvesting polymer, a fullerene, tetrahydrofuran (THF), an alcohol and water. The alcohol is isopropanol. The precursor of the light harvesting polymer is compound (1). The fullerene is PCBM. The hole transport layer is formed according to the following method: (i) coating the active layer with a solution of the hole conducting compound in water and/or an alcohol or mixture of alcohols to form a film; (ii) drying the film to form a hole transport layer. The active layer is wetted with an alcohol prior to the coating step (i). The alcohol used to wet the active layer and the alcohol used in the solution in step (i) is isopropanol. The electrode is a metal electrode. The electrode is formed by coating an ink comprising metal flakes, water and a water-soluble binder on to the hole transport layer and drying the ink. The metal electrode comprises silver. Preferred Ink: In the ink, the zinc acetate and the wetting agent are in aqueous solution. The ink further comprises AlOH(OAc)2. The ink has a composition of Zn(OAc)2.2H2O (0.1 gml-1 in water), AlOH(OAc)2 (1.5 wt.% compared with Zn(OAc)2.2H2O) and Zonyl FSO-100 (1-3 wt.% compared with Zn(OAc)2.2H2O). EXAMPLE - No suitable example given.