Ionic Liquid‐Assisted Improvements in the Thermal Stability of CH3NH3PbI3 Perovskite Photovoltaics

The instability of perovskite photovoltaic material is the key issue hindering its commercialization. Herein, we report a novel strategy to improve the thermal stability of perovskite materials containing methyl ammonium (MA) by adding a small amount of nonvolatile 1‐butyl‐3‐methylimidazolium bromine (BMIBr) ionic liquid. Nuclear magnetic resonance and scanning electron microscopy measurements show that BMIBr can anchor the MA cation via hydrogen bonding and can reduce the grain boundaries of the perovskite film. BMIBr‐doped perovskite films can tolerate heating for 50 min at 85 °C in contrast to the degradation of the undoped films at the beginning of heating. The retained photovoltaic performance of the perovskite solar cell can also be enhanced from 70 to 85% by BMIBr during thermal degradation at 85 °C for 20 min. This is a novel approach to developing perovskite photovoltaic devices with long‐term stability.