Improvement of efficiency and stability of CuSCN-based inverted perovskite solar cells by post-treatment with potassium thiocyanate

We report an inverted perovskite solar cell (PSC) based on a solution-processed CuSCN thin film for hole transporting layer. Methylammonium lead iodide (MAPbI₃) perovskite film is formed on the CuSCN layer, which shows hysteresis-less current-voltage characteristics. Post-treatment of the CuSCN film with KSCN improves power conversion efficiency (PCE) from 11.9% to 14.9% due to main increment of photocurrent density from 16.71 to 19.20 mA/cm². From the test with various salts of KX (X = SCN, I and Br) and MSCN (M = K and Na), we have found that thiocyanate anion plays more critical role in improving photovoltaic parameters. Photoluminescence (PL) is more quenched and PL decay time is faster after post-treatment with KSCN, which is indicative of better charge separation and responsible for the improved photocurrent density. In addition interface recombination, estimated by impedance spectroscopy, is suppressed by the post-treatment with KSCN, which is related to the improved open-circuit voltage. PSCs with KSCN-treated CuSCN demonstrates better photo- and humidity-stability as compared to those with untreated CuSCN, which is likely to correlate with improved interface.