Electronic, optical properties and rashba dresselhaus effect in inorganic halide perovskite

Abstract

In this thesis, the electronic and optical properties of Lead-free perovskites, CsPbI3 and Cs2AgBiBr6 were investigated. The stability of these modified crystals was verified through structural factors and formation energy. We studied the projected density of states, band structure plot, absorption coefficient and refractive index graphs, hence verifying its credibility for photovoltaic application. Lead is renowned for its toxic nature and instability towards moisture, stress etc, thus dampening the commercialization of Lead halide perovskite. To subdue this limitation, lead-free materials are being promoted, two of the suggested alternatives have been discussed in this thesis. Some of the lead atoms in Caesium lead iodide were substituted by similar cations like Barium, Calcium, Magnesium and Strontium and their respective projected DOS were plotted. The second material inspected was halide double perovskite, to ascertain its stability the formation energy and structural factors were calculated. As we know the halide double perovskites do not exhibit Rashba Effect in the 3D system, we reduced the dimensionality by introducing vacuum along a particular direction, as for 2D we increased the lattice parameter along (001) direction. On increasing separation between lattices, a reduction in van Der Wall interaction between the two layers is observed, hence transforming the 3D structure to 2D. The projected DOS, bandstructure plot, absorption coefficient and refractive index plots were observed with and without the spin-orbit coupling in materials. There is a substantial decrease in bandgap observed as 2D structure shows metallic bandstructure while the 3D material corresponds to IR bandgap with SOC and Visible region without SOC. Therefore we infer that on reducing dimensionality we observe narrowing of the bandgap of the crystal but the reduction can be done only to a limit as it fragments the crystal structure, 1D and 0D materials were found unstable.