Efficient Perovskite Solar Cells with Titanium Cathode Interlayer

Electron and hole transport layers play a critical role in high performance metal halide perovskite solar cells. Many organic and inorganic electron/hole transport layers are developed and studied in the last few years. In this work, the authors innovatively use a ultra-thin layer of titanium (Ti) as a cathode interlayer between metal electrode and perovskite film, without using any organic or inorganic electron transport layers, in planar heterojunction perovskite solar cells. X-ray photoelectron spectroscopy and soft X-ray absorption near edge structure results prove that Ti film forms a bonding layer with nitrogen (N) atoms in metylammonium anions at perovskite/Ti interface, which passivates surface defects and suppresses surface decomposition of perovskite film. The champian solar cell based on methylammonium lead iodide (CH3NH3PbI3) shows a short circuit current density of 22.5 mA cm(-2), a open circuit voltage of 1.03 V and a fill factor of 78.2%, yielding a power conversion efficiency of 18.1%. Notably, Ti has low diffusivity and serves as a compact blocking layer that prevents the diffusion of metal atoms into the perovskite layer, resulting in improved device stability. Our work shows that Ti is a promising low-cost material to replace organic and inorganic electron transporting layers for efficient perovskite solar cells.