First-Principles Prediction of the ZnO Morphology in the Perovskite Solar Cell

The hybrid halide perovskite has attracted enormous attention due to its high photovoltaic conversion (>20%). The main concern with the practical application of this technology is the poor stability of the hybrid halide perovskite. Recent studies show that the ZnO coating can substantially improve the stability of hybrid halide perovskite in the air, but the fundamental aspects, such as the epitaxial relation with perovskite and the morphology of ZnO in the coating film, remain unknown. By combining the modified phenomenological theory of Martensitic crystallography and first-principles calculations, we resolve the atomic-level structures of the interface between ZnO and MAPbI(3). We show that the primary facets of ZnO, i.e., (10 (1) over bar0) and (11 (2) over bar0) can form coherent interfaces with MAPbI(3), with low interfacial energies ranging from 0.71 to 0.89 J/m(2). With the interfacial energies, we derive the equilibrium shape of ZnO nanoparticles over MAPbI(3) substrate, which indicates that, in the equilibrium condition, the ZnO nanoparticles assemble loosely over the MAPbI(3). The electronic structures further show that the band alignment between ZnO and MAPbI(3) depends on the orientation relations of the interface. At last, we give three suggestions to improve the stability of ZnO coating layer.