Orientation Control of 2D Perovskite in 2D/3D Heterostructure by Templated Growth on 3D Perovskite

2D/3D perovskite heterostructure solar cells are promising for their stability and high power conversion efficiency (PCE). However, organic cations in the horizontally oriented 2D perovskite inhibit carrier transport, and thus, PCE is markedly suppressed when the 2D perovskite is thickened to improve stability. In this study, the orientation control of 2D perovskite on 3D perovskite was realized to overcome the trade-off between stability and PCE of 2D/3D heterostructure. 2D perovskite fabricated on (110)-oriented MAPbI2.5Cl0.5 was horizontally oriented to the substrate surface. In contrast, 2D perovskite fabricated on (200)/(112)-oriented MAPbI3 was obliquely oriented at 45° to the substrate surface. The change of orientation angle in 2D perovskite strongly depended upon the predominant crystal orientation of 3D perovskite template. The tolerance of lattice matching between 3D and 2D perovskite must allow the orientation control. This work provides a universal strategy to improve the stability of perovskite solar cells demonstrating the high PCE.