Chemical bath deposited rutile TiO ₂ compact layer toward efficient planar heterojunction perovskite solar cells

TiO ₂ is a best choice of electron transport layers in perovskite solar cells, due to its high electron mobility and stability. However, traditional TiO ₂ processing method requires rather high annealing temperature (>500 °C), preventing it from application to flexible devices. Here, we show that TiO ₂ thin films can be synthesized via chemical bath deposition below 100 °C. Typically, a compact layer of rutile TiO ₂ is deposited onto fluorine-doped tin oxide (FTO) coated substrates, in an aqueous TiCl ₄ solution at 70 °C. Through the optimization of precursor concentration and ultraviolet-ozone surface modification, over 12% power conversion efficiency can be achieved for CH ₃ NH ₃ PbI ₃ based perovskite solar cells. These findings offer a potential low-temperature technical solution in using TiO ₂ thin film as an effective transport layer for flexible perovskite solar cells.