Low-temperature photo-activated inorganic electron transport layers for flexible inverted polymer solar cells

Abstract

A simple and versatile route of forming sol-gel-derived metal oxide n-type electron transport layers (ETLs) for flexible inverted polymer solar cells (PSCs) is proposed using low-temperature photochemical activation process. The photochemical activation, which is induced by deep ultraviolet irradiation on sol-gel films, allows formation of metal oxide n-type ETLs such as zinc oxide (ZnO) and indium gallium zinc oxide films at a low temperature. Compared to poly(3-hexylthiophene)/phenyl-C-61-butyric acid methyl ester inverted PSCs with thermally annealed ZnO ETLs (optimized efficiency of 3.26 +/- A 0.03 %), the inverted PSCs with photo-activated ZnO ETLs showed an improved efficiency of 3.60 +/- A 0.02 %. The enhanced photovoltaic property is attributed to efficient charge collection from low overall series resistance and high surface area-to-geometric area ratio by the photo-activated ZnO ETLs.