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

Formamidinium lead triiodide (FAPbI(3)) 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 FAPbI(3) formation on the typical hole transport layer (HTL), high interfacial trap-state density, and unfavorable energy alignment between the HTL and FAPbI(3) result in the inferior photovoltaic performance of p-i-n (inverted) PSCs with FAPbI(3) absorber. Herein, the alpha-phase FAPbI(3) is stabilized by constructing a buffer interface region between the NiOx HTL and FAPbI(3), which not only diminishes NiOx/FAPbI(3) interfacial reactions and defects but also facilitates carrier transport. Upon the construction of a buffer interface region, FAPbI(3) 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 degrees 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 FAPbI(3) 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 alpha-phase FAPbI(3) in inverted PSCs.