Zn‐Doped Cesium Bismuth Bromide Perovskites: Impact of Structural and Morphological Modifications on Linear and Non‐Linear Optical Properties

Cesium bismuth bromide (CBB) provides a compelling lead free, non-toxic alternative in perovskite optoelectronic applications. Doping with transition metal has been employed for the improvement of photophysical characteristics in perovskites. In this study, the incorporation of heterovalent Zn²⁺ ions in CBB nanosheets and its effect on the structural, morphological, linear, and non-linear properties are investigated. Zn doping leads to a decrease in lattice strain and crystallite size eliciting a reduction in the nanosheet dimension. Combined with the morphological alteration, incorporation of Zn results in an enhancement in the UV absorbance cross section of CBB and a reduction in Urbach energy brought on by the shallow defect passivation. The electronic states of the new systems probed using first principle studies pointed to the formation of new states in the conduction band. This instigates an enhancement of third-order optical non-linearity in the perovskites. The two-photon absorption coefficient increased by a factor of three and the optical limiting threshold is reduced to half, upon incorporation of optimal amount of Zn. This study on the effects of heterovalent substitution in lead free perovskites, in modifying the electronic states and the optical properties points to augmenting novel optoelectronic applications.