Graded interface engineering of 3D/2D halide perovskite solar cells through ultrathin (PEA)2PbI4 nanosheets

2D halide perovskites have emerged as promising materials because of their stability and passivation effect in perovskite solar cells (PSCs). However, the introduction of bulky organic ammonium cations from 2D halide perovskites would decrease the device performance generally compared to the traditional 3D MAPbI(3). Incorporation of ultrathin 2D halide perovskite nanosheets (NSs) with 3D MAPbI(3) could address this issue. Herein, we report a rationally designed PSCs with dimensional graded 3D/2D MAPbI(3)/(PEA)(2)PbI4 heterojunction, in which 2D (PEA)(2)PbI4 NSs were synthesized and incorporated between 3D MAPbI(3) and hole-transporting layer. Besides the significantly improved stability, a notable increasement in power conversion efficiency (PCE) of 20% was obtained for the 3D/2D perovskite solar cells due to the favourable band alignment among (PEA)(2)PbI4 NSs and the other components. The graded structure of MAPbI(3)/(PEA)(2)PbI4 would upshift the energy level continuously, which enhances the hole extraction efficiency thus reduces the interface charge recombination, leading to the increasements of V-OC from 1.04 V to 1.07 V, J(SC) from 21.81 mA/cm(2) to 23.15 mA/cm(2) and the fill factor from 67.89% to 74.78%, and therefore an overall PCE of 18.53%. (C) 2021 Chinese Chemical Society and Institute of Materia Medica, Chinese Academy of Medical Sciences. Published by Elsevier B.V. All rights reserved.