Interface engineering in planar perovskite solar cells: Energy level alignment, perovskite morphology control and high performance achievement

We report a simple and effective interface engineering method for achieving highly efficient planar perovskite solar cells (PSCs) employing SnO₂ electron selective layers (ESLs). Herein, a 3-aminopropyltriethoxysilane (APTES) self-assembled monolayer (SAM) was used to modify the SnO₂ ESL/perovskite layer interface. This APTES SAM demonstrates multiple functions: (1) it can increase the surface energy and enhance the affinity of the SnO₂ ESL, which induce the formation of high quality perovskite films with a better morphology and enhanced crystallinity. (2) Its terminal functional groups form dipoles on the SnO₂ surface, leading to a decreased work function of SnO₂ and enlarged built-in potential of SnO₂/perovskite heterojunctions. (3) The terminal groups can passivate the trap states at the perovskite surface via hydrogen bonding. (4) The thin insulating layer at the interface can hinder electron back transfer and reduce the recombination process at the interface effectively. With these desirable properties, the best-performing cell employing a APTES SAM modified-SnO₂ ESL achieved a PCE over 18% and a steady-state efficiency of 17.54%. Impressively, to the best of our knowledge, the obtained V_OC of 1.16 V is the highest value reported for the CH₃NH₃PbI₃ (MAPbI₃) system. Our results suggest that the ESL/perovskite interface engineering with a APTES SAM is a promising method for fabricating efficient and hysteresis-less PSCs.