Quantum Well Growth Management to Smooth the Energy Transfer Pathway for Quasi‐2D Perovskite Solar Cells

Abstract Two‐dimensional (2D) perovskite solar cells (PSCs) exhibit better stability compared with three‐dimensional PSCs. However, fundamental questions remain over the chemical phase space in the 2D perovskite framework. Here, phase distribution of alternating cations in the interlayer space 2D perovskite (GA(MA) n Pb n I 3n+1 ) is regulated by using potassium salt to control the assembly behavior of colloidal particles and manage the growth of quantum well. The strong affinity between the spacer cation and sulfonate can slow down the intercalation of organic spacer cations to provide a time window for the insertion of MA + , which is conducive to forming high n phase to facilitate the charge transportation. During the crystallization process, potassium salt is extruded to the grain boundary and produce a passivation effect. In this case, the ion migration channels and inlet of water and oxygen are cut off, which is beneficial for the stability of PSCs. A power conversion efficiency of 20.90% is obtained in this work, to the best knowledge, which is the highest PCE for all reported GA(MA) 3 Pb 3 I 10 perovskite and the large‐area device (1.01 cm 2 ) shows a high efficiency of 18.73 %. Besides, the devices deliver good humidity stability.