Through thickness anisotropy in all inorganic perovskite thin films via two-step synthesis: implications for voltaic devices

Cesium-lead-bromide (CsPbBr₃) has shown promise in thin film photovoltaics due to its desirable energy band gap, charge mobility and chemical and thermal stability. The low solubility of its single crystal in organic solvents has driven development of the two-step spin-coating technique. In this work, precursor solutions of different PbBr₂ and CsBr concentrations were spin-coated and investigated via Photoelectron Spectroscopy. The properties of the Cs_xPb_yBr_z film in cross-section demonstrate this method leads to varying stoichiometries, work functions and band gaps through the thickness. This anisotropy of the perovskite thickness has ramifications for design of photovoltaic devices.