Well-organized mesoporous TiO₂ photoelectrodes by block copolymer-induced sol-gel assembly for inorganic-organic hybrid perovskite solar cells

A well-aligned mesoporous thin layer was formed by spin-coating followed by the burn-out of its organic components at 500 °C. This film, prepared by an inorganic sol-gel process using block copolymers as a sacrificial template, showed mesoporous (mp) and crack-free layers with various pore sizes depending on the amount of 1,3,5-trimethylbenzene (TMB), which acted as a swelling agent. The mesoporous photoanodes were used in the fabrication of CH₃NH ₃Pb(I_0.9Br_0.1)₃ perovskite-based solar cells. The cells showed overall power conversion efficiencies of 11.7% and 12.8% with the 10 and 15 nm mp-layers, respectively. The superior performance shown in the 15 nm mp-layers may be attributed to the easier filling of CH ₃NH₃Pb(I_0.9Br_0.1)₃ by bigger pore sizes, and the efficiency is comparable with that of the reference cell fabricated by TiO₂ paste. This template-induced self-organizing sol-gel process was shown to be a useful technique for depositing mesoporous photoanodes in the fabrication of perovskite-based solar cells.