Structural Stabilities and Electronic Properties of High-Angle Grain Boundaries in Perovskite Cesium Lead Halides

Organometal trihalide perovskites are emerging as very promising photovoltaic materials, which is rivaling that of single crystal silicon solar cells despite their polycrystalline nature with relatively high density of grain boundaries (GBs). There is a lack of understanding of the effects of GBs on halide perovskites as their presence in silicon and other photovoltaic materials is generally detrimental to their photovoltaic properties. Using first-principles calculations, we systematically investigate the geometric structures of high-angle tilt GBs in halide perovskites CsPbX3 (X = Cl, Br, and I) starting from the coincidence site lattice model and refining using crystal shifts and lattice expansion. Electronic density of states calculations reveal that GBs in halides perovskites do not generate midgap states because Of the large distance between the unsaturated atoms and the atomic reconstructions in the GB region. However, we show that the GBs can induce different very shallow states near the valence band edge that can hinder hole diffusion. We further extend the results to MAPbI(3) GBs and also show their benign, effect on optoelectronic properties.