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. - Highlights: • Crystalline TiO₂ films with different structures were synthesized by sol-gel method. • Power conversion efficiency greatly enhanced by tuning the TiO₂ films' structures. • Optimized devices achieved a power conversion efficiency of 3.56%. • Optimized devices present excellent stability performance in argon atmosphere