Boosting Long-Term Stability of Pure Formamidinium Perovskite Solar Cells by Ambient Air Additive Assisted Fabrication

Due to the high industrial interest for perovskite-basedphotovoltaic devices, there is an urgent need to fabricate them under ambient atmosphere, not limited to low relative humidity (RH) conditions.The formamidinium lead iodide (FAPI) perovskiteα-black phase is not stable at room temperature and is challenging to stabilize in an ambient environment. In this work, we show that pure FAPI perovskite solar cells(PSCs) have a dramatic increase of device long-term stability when preparedunder ambient air compared to FAPI PSCs made under nitrogen, bothfabricated withN-methylpyrrolidone (NMP). TheT80 parameter, the time in which the efficiency drops to 80% of the initial value, increases from 21 (inN2) to 112 days (in ambient) to 145 days if PbS quantum dots (QDs) are introduced as additives in air-prepared FAPI PSCs. Furthermore, by adding methylammonium chloride (MACl) the powerconversion efficiency (PCE) reaches 19.4% and devices maintain 100% of the original performance for at least 53 days. The presence of Pb−O bonds only in the FAPIfilms prepared in ambient conditions blocks the propagation ofα-toδ-FAPI phaseconversion. Thus, these results open the way to a new strategy for the stabilization in ambient air toward perovskite solar cells commercialization.