PEAI-Based Interfacial Layer for High-Efficiency and Stable Solar Cells Based on a MACl-Mediated Grown FA0.94MA0.06PbI3 Perovskite

Abstract

Among the three-dimensional (3D) organic–inorganic hybrid perovskites (OIHPs), mixed formamidinium and methylammonium cation lead iodide is one of the most promising for solar cell application. After optimizing the use of a methylammonium chloride (MACl) additive for the preparation of compact, high-quality, and large crystal grain layers made of a pure α-phase perovskite with the FA_0.94MA_0.06PbI₃ composition, the treatment of the perovskite surface by a 2-phenylethylammonium iodide (PEAI) solution has been performed. This treatment, without any thermal annealing, leads notably to the spontaneous formation of a crystallized (PEA)₂PbI₄ two-dimensional (2D) perovskite nanolayer at the film surface due to partial organic cation dissolution. This buffer layer is shown to favor a fast transfer of the holes toward the hole transporting layer (HTL) and to reduce the recombinations at and near the perovskite/HTL interface in perovskite solar cells (PSCs). It is shown to boost their maximum power conversion efficiency (PCE) from 20.37 to 22.18%, while the hysteresis becomes negligible. A comprehensive study of the electrical response of the device has been performed. The electrical impedance spectroscopy (EIS) measurements have been fitted with ad hoc equivalent electrical circuits. The electrical responses due to interface stabilization, the intrinsic dielectric relaxation of the perovskite, and the charge depletion and charge recombinations have been distinguished. The low-frequency capacitance is analyzed as a charge recombination capacitance. The perovskite surface buffer layer is notably shown to suppress charge recombinations from the boosting of the high- and low-frequency recombination resistances as well as from the marked decrease of the low-frequency recombination capacitance. The prepared devices are proven to be especially resistant to electrical stresses, light irradiation, and moisture.