Perovskite solar cells based on bottom-fused TiO₂ nanocones

Compared to the fast electron transport in perovskite and rapid electron injection from perovskite to TiO₂ nanoparticle scaffold, the slower electron transport rate in mesoporous TiO₂ is reported to be a hindrance factor for power conversion efficiency. One-dimensional nanomaterials are believed to show faster carrier transport rate. In this paper, vertically aligned one-dimensional TiO₂ nanocones on transparent conducting oxide were synthesized and utilized as a promising scaffold for perovskite solar cells. A simple concentration-dependent CH₃NH₃PbI₃ seeding spin-coating method was developed to effectively improve the surface coverage at low cost. The resultant perovskite solar cells realized an average power conversion efficiency up to 11%, which is higher than that of rectangular TiO₂ nanorods-based device. Besides the faster electron transport rate and slower recombination in such one-dimensional nanostructures, we attribute the superior performance of the nanocone-based device to the fact TiO₂ nanocone arrays allow more CH₃NH₃PbI₃ to deposit. By scaling up the nanocone-based devices to 1.2 cm², they yielded a decent average power conversion efficiency of ∼6%. The combination of TiO₂ nanocones with perovskite paves a way to take full advantage of one-dimensional nanomaterials and organic-inorganic perovskites for photovoltaic applications.