Exploring the physical properties of cubic CsGeBr3-nIn (n= 0, 1, 2, 3) compounds: Ab initio calculations of perovskites prospective for the application in solar cells

The cubic perovskites CsGeBr3-nIn (n = 0, 1, 2, 3) were investigated using the density functional theory (DFT) for their structural, electronic, and optical properties. The present DFT calculations are carried out using three models for exchange-correlation potential, namely PBE, mBJ, and YS-PBE0. The bandgap decreases in the above sequence of compounds except CsGeBrI2, which reveals the smallest bandgap. The mBJ approximation has a larger bandgap than the PBE and smaller than the YS-PBE0. Results of calculations within the YS-PBE0 approach for CsGeBr3 and CsGeI3 agree well with QSGW + SO results. The CsGeBr3-nIn compounds are direct bandgap semiconductors and CBM and VBM are positioned at the R point and determined mainly by Ge s-states and Br(I) p-states, respectively. Analysis of optical properties shows that the DFT calculations within the PBE model consistently produce the highest static dielectric function values, while the YS-PBE0 method gives the smallest values. The curves of optical coefficients shift toward lower energies when decreasing the Br atoms in CsGeBr3-nIn. The studied compounds are semitransparent in the infrared and visible regions and show promising potential for photovoltaic applications, including solar cells.