Formamidine formate as the multifunctional modulator at buried interface for efficient FAPbI3 perovskite solar cells

Interface modification is recognized as an effective strategy to promote the performance of perovskite solar cells (PSCs) especially after the thorough optimization on film fabrication process. Device performance is augmented considerably by passivating the perovskite surface utilizing variety of materials. On the other hand, buried interface revealed a higher defect density than top surface, hence, rational optimization of buried interface is getting paramount for the further amelioration on efficiency and stability of PSCs. Herein, formamidine formate (FAFa) with both carboxyl and amino groups is employed to modify the buried interface between SnO2 and perovskite. It is demonstrated that FAFa treatment can enhance the electrical properties of SnO2 and optimize the band alignment. Meanwhile, it improves the contact performance by constructing a chemical bridge at the buried interface. Moreover, it endows high quality perovskite by modulating the growth process. Consequently, the power conversion efficiency of FAPbI3 PSCs is elevated substantially from 20.89% to 23.11% mainly benefitted from the suppressed carrier recombination and facilitated electron extraction at the buried interface. Meanwhile, corresponding device illustrated reinforced durability both in inert and atmospheric environment. Our work presented a convenient way to modify the buried interface for the further enhancement of PSC performance.