Abstract
Despite three-dimensional (3D) perovskite solar cells (PSCs) having a high power conversion efficiency (PCE) beyond 22%, they are unstable under humidity, oxygen and ultraviolet light. Two-dimensional (2D) perovskites exhibit high stability but have poor photovoltaic performance. To simultaneously enhance the PCE and stability of PSCs, we designed new mixed-dimensional (MD) PSCs by introducing HOCH2CH2NH3I (EAI) into (FAPbI(3))(0.85)(MAPbBr(3))(0.15) 3D perovskite. The MD devices made with [(EA)(2)PbI4](x)[(FAPbI(3))(0.85)(MAPbBr(3))(0.15)](1-x) exhibit outstanding photovoltaic performance with an improved PCE of 18.79% due to the outstanding crystal structure, superior surface morphology, enhanced charge transport and reduced carrier recombination. More importantly, the MD devices display markedly improved stability against humidity, heat and UV light. After exposing to about 50% relative humidity (RH) for over 1700 hours (h), the unsealed devices retain about 85% of the initial PCE. After exposing to air at 85 degrees C for 220 h and exposing to continuous UV irradiation for 13 h, all the unsealed devices retain PCEs of about 60% of the initial value. These results demonstrate that designing a novel MD perovskite is a significant strategy for improving both photovoltaic performance and stability of PSCs.