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

Due to the high industrial interest for perovskite-based photovoltaic 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) perovskite alpha-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 prepared under ambient air compared to FAPI PSCs made under nitrogen, both fabricated with N-methylpyrrolidone (NMP). The T-80 parameter, the time in which the efficiency drops to 80% of the initial value, increases from 21 (in N-2) 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 ( CI) the power conversion efficiency (PCE) reaches 19.4% and devices maintain 10096 of the original performance for at least 53 days. The presence of Pb-O bonds only in the FAPI films prepared in ambient conditions blocks the propagation of alpha- to delta-FAPI phase conversion. Thus, these results open the way to a new strategy for the stabilization in ambient air toward perovskite solar cells commercialization.

Automated summary

This study demonstrates that pure FAPI perovskite solar cells prepared in ambient air exhibit greater long-term stability compared to those fabricated under nitrogen. The addition of PbS quantum dots and methylammonium chloride can enhance the performance and stability of these devices even further.