Formate Additive for Efficient and Stable Methylammonium-Free Perovskite Solar Cells by Gas-Quenching.

In order to promote the commercialization of perovskite solar cells, gas-quenching is considered to be a promising technique for perovskite film fabrication. However, when handling with methylammonium-free (MA-free) perovskites, it is often difficult to obtain high-quality perovskite films by gas-quenching. Herein, formate additives are employed to regulate the crystallization of MA-free perovskite, and improve the quality of perovskite films. Different additives of formamidine formate (FAFO) and potassium formate (KFO) is compared to investigate the role of formate groups in the crystallization of perovskite films prepared by gas-quenching. The FAFO additive facilitates the perovskite crystallization in (001) orientation whereas KFO favors for (111) orientation. The MA-free device with addition of FAFO demonstrate a champion power conversion efficiency of 20.94 %, compared to that of 20.14 % for KFO devices. In addition, FAFO device also exhibits improved thermal stability in ambient condition without encapsulation, extending the T 80 lifetime by 18 times compared to the pristine device.