Texture Formation in Polycrystalline Thin Films of All Inorganic Lead Halide Perovskite

Controlling grain orientations within polycrystalline all inorganic halide perovskite solar cells can help increase conversion efficiencies toward their thermodynamic limits; however, the forces governing texture formation are ambiguous. Using synchrotron X ray diffraction, mesostructure formation within polycrystalline CsPbI2.85Br0.15 powders as they cool from a high temperature cubic perovskite alpha phase is reported. Tetragonal distortions beta phase trigger preferential crystallographic alignment within polycrystalline ensembles, a feature that is suggested here to be coordinated across multiple neighboring grains via interfacial forces that select for certain lattice distortions over others. External anisotropy is then imposed on polycrystalline thin films of orthorhombic gamma phase CsPbI3 xBrx perovskite via substrate clamping, revealing two fundamental uniaxial texture formations; i I rich films possess orthorhombic like texture lt;100 gt; out of plane; lt;010 gt; and lt;001 gt; in plane , while ii Br rich films form tetragonal like texture lt;110 gt; out of plane; lt;110 gt; and lt;001 gt; in plane . In contrast to relatively uninfluential factors like the choice of substrate, film thickness, and annealing temperature, Br incorporation modifies the gamma CsPbI3 xBrx crystal structure by reducing the orthorhombic lattice distortion making it more tetragonal like and governs the formation of the different, energetically favored textures within polycrystalline thin film