Bidentate ligand application for perovskites passivation

Perovskite solar cells (PSCs) are a type of solar cell that has an ABX₃ structure and have found applications in photoluminescence, sensors and actuators, ferroelectric and piezoelectric devices, semiconductors, and supercapacitors. Despite being cheaper and easier to fabricate than the silicon-based solar cells, their use has been hampered by the accompanying surface defects leading to thermal and moisture instability and reduced photovoltaic performances. Bidentate ligands have been reported to improve the photovoltaic properties of perovskites by increasing the short-circuit current density (J_sc), the open-circuit voltage (V_oc), the fill factor (FF), the power conversion efficiency (PCE), and the hysteresis. Passivation of some PSCs has led to certified efficiencies of 26.4% and 33.7% in a single and heterojunction materials, respectively. In addition to the improved photovoltaic performances, bidentate ligand-derived perovskites have been reported to improve operational stability wherein the perovskite retained above 99% of its earliest power conversion efficiency even after 5000 h of constant heating at 80 °C, humidity of 60%, or illumination of 3.0 W. Beside passivation using bidentate ligands, the use of impurities for doping and interface optimization has also been linked to improved perovskite performance. However, with doping, there is an introduction of more uncoordinated metal ions at the perovskite surface during surface optimization. The nicotinimidamide, N,N-diethyldithiocarbamate and the isobutylhydrazine were the most outstanding bidentate ligands used for the passivation of perovskite, showing power conversion efficiency of 25.30, 24.52, and 24.25% respectively. We also observed that the replacement of MA in MAPbI₃ (methylammonium lead iodide) perovskite reported by Mas-Montoya with FA, giving FAPbI₃ (formamidinium lead iodide) perovskite reported by Liu's, group, led to improvement in the efficiency from 16.20 to 24.52% using N,N-diethyldithiocarbamate for passivation. This review x-rayed the role of bidentate ligands in the surface passivation of perovskite solar cells leading to improved stability and photovoltaic performances.