Self‐Assembled 1D/3D Perovskite Heterostructure for Stable All‐Air‐Processed Perovskite Solar Cells with Improved Open‐Circuit Voltage

Abstract Environmental instability and photovoltage loss induced by defects are inevitable obstacles in the development of all‐air‐processed perovskite solar cells (PSCs). In this study, the ionic liquid 1‐ethyl‐3‐methylimidazolium iodide ([EMIM]I) is introduced into the hole transport layer/three‐dimensional (3D) perovskite interface to form a self‐assembled 1D/3D perovskite heterostructure, which significantly reduces iodine vacancy defects and modulates band energy alignment, resulting in pronouncedly improved open‐circuit voltage ( V oc ). As a result, the corresponding device exhibits a high power conversion efficiency with negligible hysteresis and a high V oc of 1.14 V. Most importantly, together with the high stability of the 1D perovskite, remarkable high environmental and thermal stabilities of the 1D/3D PSC devices are achieved, which maintain 89 % of unencapsulated device initial efficiency after 1320 h in air and retain 85 % of the initial efficiency when heated at 85 °C for 22 h. This study affords an effective strategy to fabricate high‐performance all‐air‐processed PSCs with outstanding stability.