Hindered Amine Light Stabilizers Increase the Stability of Methylammonium Lead Iodide Perovskite Against Light and Oxygen

Methylammonium lead iodide perovskite (MAPI) is a promising material for highly-efficient photovoltaic devices. However, it suffers from photooxidation, which imposes strict requirements for its protection from oxygen during processing and operation. Herein we report the unprecedented stabilization effect of hindered amine light stabilizer (HALS) on methylammonium iodide (MAI) and MAPI against photooxidation. We found that HALS prevents the degradation of MAI by inhibiting the oxidation of iodide to iodine. Chemical modification of HALS allows us to incorporate it in MAPI films which extends the resistivity of MAPI against photodegradation at ambient air from a couple of hours to several days, while causing no significant changes in key properties, such as optical absorption and charge transport. These results represent an important advance in the fight against MAPI decomposition and demonstrate for the first time that antioxidants improve the stability of MAPI.