An ambient process for hole transport layer-free highly stable MAPbI3 by addition of MACl for efficient perovskite solar cells

Abstract

Methylammonium lead iodide (MAPbI₃) is a front-runner material for efficient perovskite solar cells (PSCs) due to its high light-absorption coefficient, suitable bandgap, and superior charge carrier mobility. However, high-quality photoactive MAPbI₃ (MAPI) perovskite thin-films are usually fabricated in controlled atmospheric conditions (inside a glove box) and annealed at high temperature (generally >120 °C for 20 min). Here, we report a facile method to fabricate high quality MAPbI₃ (MAPI) thin-films by the simple addition of an MA-based volatile additive, i.e., methylammonium chloride (MACl). The optimized amount of MACl in the perovskite solution produced a highly crystalline and optically active MAPI black perovskite phase at room temperature under ambient atmospheric conditions. MACl not only regulates the surface morphology of the perovskite films, but also the intermediate phases by altering the formation energy of the perovskite material. MACl lowered the formation energy of the MAPI perovskite resulting in the room temperature formation of phase pure MAPI perovskite under ambient conditions. Finally, we assembled perovskite solar cell devices with an HTL-free carbon-based architecture to determine the photovoltaic performance of the prepared thin-films. Our champion device showed a power conversion efficiency as high as 7.11% with an open circuit voltage of 0.98 V, short circuit current density of 11.03 mA cm⁻² and a fill-factor of 65.86%. The device was stable over 10 days under ambient conditions and retained ∼80% of its initial efficiency. These results are favourable for large-scale fabrication to make it commercially viable.