The influence of the buried interface on the orientational crystallization and thermal stability of halide perovskite thin films†

Abstract

Metal halide perovskites are promising materials for efficient solar energy conversion, holding promise as the next generation of photovoltaics. However, to fully realize the potential of perovskite solar cells (PSCs) and advance the technology towards commercialization, several stability issues still need to be addressed. Numerous approaches have already been explored to improve the stability of PSCs, with oriented crystal growth offering an effective strategy to not only improve stability but also increase device performance due to the photoelectric anisotropy of perovskites. In this work, we systematically monitor the influence of the most common underlayers used in regular and inverted PSCs on the oriented growth of formamidinium–cesium lead iodide (FA_0.9Cs_0.1PbI₃) perovskites. Employing crystallographic, morphological, and spectroscopic characterization techniques, we show that the preferred orientation driven by the underlayers controls perovskite phase segregation under thermal stress, correlating it with the stability of perovskite films and solar cells subjected to 500 h of continuous heating at 85 °C.