Eutectic molecule ligand stabilizes photoactive black phase perovskite

Abstract

Formamidinium-rich triiodide perovskites show great promise as light-absorption layers for next photovoltaic technology. However, the intricate process of phase transformation during the crystallization of this perovskite typically results in the presence of undesired hexagonal phases, leading to a degradation in solar cell efficiency and stability. Here we report the use of a hydrogen-bonded eutectic molecule (EM) as a [PbI6]4− octahedra ligand to promote the dominant formation of corner-sharing octahedra. Our results demonstrate that the increased ratio of corner-sharing octahedra to face-sharing octahedra can prompt a complete phase transformation and facilitate the formation of pure cubic structure perovskite. Perovskite solar cells based on EM-fabricated films provide a power conversion efficiency of 25.8% (certified 25.7%) and excellent stability with a T95 lifetime of ~2,000 h. The use of a hydrogen-bonded eutectic molecule as a ligand stabilizes black phase perovskite, resulting in solar cells with a T95 lifetime of 2,000 h and an efficiency of 25.8%.