Modulating Band Alignment in Mixed Dimensionality 3D/2D Perovskites by Surface Termination Ligand Engineering

Three-dimensional (3D)/two-dimensional (2D) mixed dimensional perovskites have potentially overcome the stability issues of conventional 3D perovskites without significantly compromising the solar cell performance. 3D/2D perovskite heterostructures rely on the alignment of energy levels across the 3D/2D interface, which determines carrier confinement and possibly charge separation. Using state-of-the-art first-principles calculations, we show that the confined dipoles of spacer cations and the perovskite surface termination have a crucial role in determining interfacial energy alignment. Considering the experimentally employed BA2PbI4 (BA = n-butylammonium) and AVA2PbI4 (AVA = protonated aminovaleric acid) 2D perovskite interfaces with the prototypical MAPbI3 3D perovskite, we systematically investigate the band alignment at the interfaces of 3D and 2D quantum wells considering different types of surface terminations. Our study shows that BA2PbI4 has favorable alignment of band edges with MAPbI3 irrespective of the surface termination of MAPbI3, however, with the alteration of the band edge positions between 2D and 3D parts depending on surface termination. On the other hand, the alignment of AVA2PbI4 with MAPbI3 is very much sensitive to surface termination, having favorable alignment by virtue of confined interface dipoles of the-COOH groups. This study provides a global picture of the interface engineering in 3D/2D perovskites, setting the required background to further explore the anchoring of hole/electron transport materials at the preferential side of the film for improved carrier extraction.