Enhanced photovoltaic performance of inverted polymer solar cells by tuning the structures of titanium dioxide

Inverted polymer solar cells using TiO2 film as electron transporting layer were fabricated with the structure of fluorine-doped tin oxide/TiO2 films/poly(3-hexylthiophene): [6,6]-phenyl-C61-butyric acid methyl ester/Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)/Ag. By tuning the crystalline structure of TiO2 films, the photovoltaic performance of the devices was remarkably enhanced. TiO2 was prepared by sol-gel method and their structures, morphologies and transmittance were characterized by X-ray diffraction, scanning electron microscope, and UV-visible spectrophotometer. Interestingly, for TiO2-3 film, which was prepared with tetrabutyl titanate, acetyl acetone and ethanol in a ratio of 1:0.5:6, the open-circuit voltage and fill factor of the device were up to 0.6 V and 64.8%, respectively, and the power conversion efficiency of TiO2-3 film was achieved up to 3.56% with the current density of 9.18 mA/cm2 under an AM 1.5 G (100 mW/cm2) irradiation intensity. In the meanwhile, the stabilities of these devices were also studied and results showed that our work was better than the corresponding devices of conventional structure.