Enhanced Efficiency and Stability of Triple-Cation Perovskite Solar Cells through Engineering of the Cell Interface with Phenylethylammonium Thiocyanate.

Abstract

It is reported that the tricationic mixed halide perovskite Cs_x(FA_yMA_1-y)_1-xPb(I_zBr_1-z)₃ (CsFAMA) possesses a stable crystal structure and outstanding bandgap tunability, rendering it one of the most competitive candidates for commercial perovskite solar cells (PSCs). Nevertheless, the numerous defects at the interface of the tricationic perovskite give rise to a significant constraint on the light capture performance of the device. Simultaneously, water molecules form intermediate compounds with the perovskite at the interface via hydrogen bonds, accelerating the degradation of the perovskite. This study reports the introduction of two-dimensional (2D) phenylethylthiocyanate (PEASCN) at the interface of three-dimensional (3D) perovskite. This approach significantly passivates the surface defects of the perovskite. Concurrently, due to the propensity of the organic ammonium cation PEA⁺ to interact with the FA⁺ base within the perovskite, SCN^- is exposed outward to form a small-molecule hydrophobic layer. This method markedly reduces the loss of charge recombination and significantly enhances the device stability. The results indicate that the efficiency of the conventional device treated solely with PEASCN is as high as 23.94%. The unsealed device retains 85.12% of its initial efficiency after being placed in a conventional environment for 500 h. Furthermore, this surface passivation and hydrophobic strategy can be universally applicable to perovskite types with a high FA⁺ content.