Mechanism of segmentation of lead halide perovskite at interfaces with GaN and ZnO

Abstract

Structural degradation is a main problem for the commercialization of the organic lead halide perovskite solar cells. A role of the interfaces with the transparent electrodes, in this process, could be made clear by the combined ab initio calculations and the X-ray absorption measurements. The junctions of MAPbI3(MA = CH3NH3) with pure GaN and ZnO crystals, oriented with the polar [0 0 0 1] and [0 0 0 −1] surfaces, are theoretically investigated by means of the density functional theory (DFT) and simulations of the X-ray absorption near-edge spectroscopy (XANES). Unwanted decomposition of the perovskite, into the layers which are parallel to the interface, coexists with a strong binding of the halide atom at GaN [0 0 0 1] and ZnO [0 0 0 1]. In contrast, at the interfaces with the [0 0 0 −1]-oriented GaN and ZnO, aforementioned segmentation of the perovskite does not occur, because binding of the halide atom is much weaker. Thus, the adsorption properties of the halide atom at semiconductor surface might be a precondition for a choice of the substrate to grow the stable perovskite film. The I-core K-edge XANES spectra at the interface atoms contain a fingerprint of the iodide adsorption strength.