Strain-relaxed tetragonal MAPbI3 results in efficient mesoporous solar cells

Abstract

In mesoporous organo-halide perovskite solar cells, the coexistence of tetragonal phase and cubic phase in the perovskite layer is found to result in strained crystal structure at the mesoporous TiO 2 (mp-TiO 2 )/perovskite heterointerface. This results in structural defects pinholes, grain boundaries, and interfacial porosity which is detrimental towards photovoltaic performance and device stability. The strain at the interface originates from the lattice mismatch between the mp-TiO 2 nanoparticles (NPs) and perovskite. Here, a transformative approach is demonstrated to realize relaxed and high purity tetragonal phase MAPbI 3 (RP) near the mp-TiO 2 interface region. This approach involves inserting a ~2 nm lattice matched buffer layer of cubic CsPbBr 3 between mp-TiO 2 NPs and MAPbI 3 , which serves as a template for epitaxial growth for top MAPbI 3 . The solar cell with relaxed MAPbI 3 shows a power conversion efficiency (PCE) of 22.12% with significantly enhanced environmental, light, and thermal stability. • Strain engineering is invoked to achieve strain-relaxed and tetragonal MAPbI 3 at the mp-TiO 2 /MAPbI 3 heterointerface. • The modified relaxed MAPbI 3 -based device exhibits a PCE of 22.12%. • The modified devices show enhanced environmental, thermal, and light stabilities.