DFT insights on lead-free double perovskite A2(Ag/In)BrO6 (A=Ca, Sr, Ba) phase for optoelectronic applications

Abstract

The first principle investigation on the structural, electronic, optical, thermal and thermoelectric properties of lead-free double perovskite A₂(Ag/In)BrO₆ (A=Ca, Sr, Ba) in the cubic phase has been performed using the Full Potential Linearized Augmented Plane Wave (FP-LAPW) method in the framework of DFT (Density Functional Theory). The computational structural properties shows the most stable structure in the phase group of Fm3m (225) for the proposed compounds A₂(Ag/In)BrO₆ (A=Ca, Sr, Ba). Modified Becke–Johnson (mBJ) potential embedded in the WIEN2K code is used to calculate the band structure. The obtained band structure plots and Density of State histograms depicts that the proposed materials are conductor or slightly the stage ahead from semiconductor whereas the parent material namely Ba₂NaBrO₆ is a direct band gap semiconductor. The total and partial density of states shows that the electron contribution towards the Fermi region is predominant due to O-p orbitals, Ag-d orbitals and In-p orbital. There is a negligible contribution arising from the alkaline earth metals namely Ba, Sr and Ca. In view of optical properties analysis, the parameters such as refractive index, dielectric function, reflectivity, optical conductivity exhibits strong absorption of photons and great potential to conduct electrons in the UV region whereas Ba₂InBrO₆ has fascinating optical properties in the UV region. Hence, among these six novel compounds, Ba₂InBrO₆ has the preferable photovoltaic performance and conversion efficiency, making it has the potential candidate of photovoltaic application in the UV region. The thermoelectric properties such as Seebeck coefficient, power factor and thermoelectric figure of merit are computed to all the proposed compounds and found Ba₂NaBrO_6, Ca₂AgBrO₆ are more efficient due to its remarkable obtained power factor.