Multiple bonding effects of 1-methanesulfonyl-piperazine on the two-step processed perovskite towards efficient and stable solar cells

Interfacial engineering is a highly effective strategy to improve device performance of perovskite solar cells (PSCs) by alleviating the defect-induced non-radiative recombination, while reports on defect passivation of the two-step processed perovskite films are quite limited to date. Herein, a new type of multifunctional molecule, 1-methanesulfonyl-piperazine (MP), is applied to modify the perovskite film that is fabricated via a two-step process. The introduction of MP passivation enables multiple bonding interactions with perovskite film, i.e., hydrogen bond, Pb-O and Pb-N dative bonds, resulting in significantly reduced trap density and effectively suppressed non-radiative recombination. Moreover, the MP-modified perovskite films show improved crystallinity with decreased PbI2 residuals, which is conducive to both carrier transport and stability of the resultant devices. As a consequence, the MP-modified devices present an impressive power conversion efficiency (PCE) of 23.4% along with enhanced stability, e.g., the unencapsulated device retains 88% of its original PCE even subject to thermal aging at 85 ℃ for 600 h. This work opens up an avenue to explore functional materials for high-performance and long-term stable PSCs.