Bifunctional ligand-induced preferred crystal orientation enables highly efficient perovskite solar cells

Crystallization orientation and the buried interface have been proven to be key factors determining the efficiency of perovskite solar cells (PSCs). Here, we report a facile strategy to concomitantly induce (100)-oriented perovskite and improve buried interface by incorporating a bifunctional ligand 2-(methylthio) ethylamine hydrochloride (METEAM) into perovskite precursor solution. METEAM molecules preferentially adsorb on (100) facets of perovskite via strong interactions with perovskite lattice to induce oriented perovskite crystallization. Meanwhile, METEAM molecules spontaneously aggregate at the buried interface and operate as a bridge between the perovskite and tin oxide (SnO₂) electron transport layer to bidirectionally passivate their defects. As-prepared perovskite films exhibit suitable energy level and high mobility for interfacial charge transfer, low trap state density, and long carrier lifetime. The resultant conventional-structure PSC devices deliver a power conversion efficiency (PCE) of 26.1% (certified 25.8%) with improved operational and ambient stabilities, which is among the highest PCE of conventional PSCs.