Hybrid inverted organic photovoltaic cells based on nanoporous TiO2 films and organic small molecules

Solar cells based on nanoporous TiO2 films with an inverted structure of indium tin oxide (ITO)/TiO2/copper phthalocyanine (CuPc):fullerene (C60)/CuPc/poly(3,4-oxyethyleneoxythiophene):poly(styrene sulfonate) (PEDOT:PSS)/Au were fabricated. The best overall photovoltaic performance undergoing a series of device optimization was achieved with the device of ITO/dense TiO2 (30 nm)/nanoporous TiO2 (130 nm)/C60:CuPc (1:6 weight) (20 nm)/CuPc (20 nm)/PEDOT:PSS (50 nm)/Au (30 nm). The device using the nanoporous TiO2 films has better photovoltaic properties compared to those using dense TiO2 films. Higher photovoltaic performances were obtained by introducing a coevaporated layer of C60:CuPc between TiO2 and CuPc. The stability of inverted structure was better than that of the normal device, which gives a promising way for fabrication of solar cells with improved stability.