Air Stable Photovoltaic Device

A method of forming a conducting polymer based photovoltaic device comprising the steps of : (a) providing a transparent first electrode; (b) providing the transparent first electrode with a layer of metal oxide nanoparticles, wherein the metal oxide is selected from the group consisting of : TiO2, TiOx and ZnO; (c) providing the layer of metal oxide nanoparticles with a bulk hetero junction layer comprising metal oxide nanoparticles and a hole conducting polymer containing thermocleavable groups, wherein the metal oxide is selected from the group consisting of : TiO2, TiOx, CeO2, Nb2O5 and ZnO; (d) heating the bulk heterojunction layer to cleave the thermally cleavable groups to produce an insoluble hole containing polymer; (e) providing the bulk heterojunction layer with a hole transporting layer; and (f) providing the hole transporting layer with a second electrode. Also a conducting polymer based photovoltaic device, and polymeric compounds suitable for use in such devices and methods.