Stabilization of α‐phase FAPbI3 via Buffering Interfacial Region for Efficient p–i–n Perovskite Solar Cells

Abstract

AbstractFormamidinium lead triiodide (FAPbI3) with an ideal bandgap and good thermal stability has received wide attention and achieved a record efficiency of 26% in n–i–p (regular) perovskite solar cells (PSCs). However, imperfect FAPbI3 formation on the typical hole transport layer (HTL), high interfacial trap‐state density, and unfavorable energy alignment between the HTL and FAPbI3 result in the inferior photovoltaic performance of p–i–n (inverted) PSCs with FAPbI3 absorber. Herein, the α‐phase FAPbI3 is stabilized by constructing a buffer interface region between the NiOx HTL and FAPbI3, which not only diminishes NiOx/FAPbI3 interfacial reactions and defects but also facilitates carrier transport. Upon the construction of a buffer interface region, FAPbI3 inverted PSC exhibits a high‐power conversion efficiency of 23.56% (certified 22.58%) and excellent stability, retaining 90.7% of its initial efficiency after heating at 80 °C for 1000 h and 84.6% of the initial efficiency after operating at the maximum power point under continuous illumination for 1100 h. Besides, as a light‐emitting diode device, the FAPbI3 inverted PSC can be directly lit with an external quantum efficiency of 1.36%. This study provides a unique and efficient strategy to advance the application of α‐phase FAPbI3 in inverted PSCs.