Enhanced stability of α-phase FAPbI3 perovskite solar cells by insertion of 2D (PEA)2PbI4 nanosheets

Abstract

Methylammonium (MA) is one of the main obstacles that hold back the commercialization of perovskite solar cells (PSCs). Formamidinium (FA)-based perovskite is a promising photovoltaic material due to its higher thermal stability and smaller bandgap. However, despite the introduction of Cs⁺ in FAPbI₃, the photoactive α-phase FAPbI₃ can quickly transform into a non-perovskite hexagonal phase δ-FAPbI₃, which limits its use in perovskite solar cells. In this work, we show that the dispersion of 2D (PEA)₂PbI₄ nanosheets into a Cs_0.1FA_0.9PbI₃ thin film successfully prevents the transformation of the α-phase Cs_0.1FA_0.9PbI₃ to the δ-phase. Because of the 2D (PEA)₂PbI₄ nanosheets, a higher quality perovskite thin-film was obtained with a longer carrier lifetime, lower trap state density, and enhanced stability. The resulting device achieves a high power conversion efficiency of 20.44%, which is one of the highest for MA-free perovskites and retains 82% of its initial efficiency after 800 h of aging study.