Ion Compensation of Buried Interface Enables Highly Efficient and Stable Inverted MA‐Free Perovskite Solar Cells

The development of inorganic hole-transporting materials (HTMs) is one of the most reliable ways to improve the stability of perovskite solar cells (PSCs). However, the un-optimal buried interfacial contacts and the defects located at the inorganic HTMs/perovskite interface restricted the device's performance. Herein, a phase-pure CuScO2 has been synthesized and further employed as mesoporous HTM in inverted PSCs. Surprisingly, a facile pretreatment of the hole-transport layer by a formamidine salt compensates the I- vacancy of the buried perovskite film, thus regulating the interfacial band energy alignment between the HTM and perovskite. This ion compensation strategy can not only in situ repair the ion loss and improve the built-in electric field, but also decrease the charge injection barrier and suppress the non-radiative interfacial recombination. Benefiting from these merits, the resulting methylammonium-free (MA), Cs/FA-based PSCs displays a power conversion efficiency (PCE) of 22.42% along with excellent thermal and light stability. Moreover, the pre-buried treatment strategy can be extended to MA-containing CsFAMA triple-cation perovskite film, and a champion inverted device delivers a PCE of 23.11%. This study offers a new avenue to the rational design of HTMs for highly efficient and stable PSCs.