A Comparative Study of the Structural and Electronic Properties of Orthorhombic and Cubic CsPbI3 and Trigonal CsGeI3 using First-Principles Calculations

Lead-free halide perovskites are of great importance as prospective materials for efficient solar cells. Germanium is a very promising non-toxic alternative to lead. In this study, the crystal configuration, projected density of states and band structure of the trigonal CsGeI
3
, the yellow and the quenched black orthorhombic CsPbI
3
, and the cubic CsPbI
3
were investigated using the density functional theory with Perdew-Burke-Ernzerhof functional. Our calculations showed that for the CsGeI
3
, the valence band maximum is mainly contributed by the I 5p and Ge 4s orbitals whereas the conduction band minimum is mainly contributed by the Ge 4p orbitals. The replacement of Pb with Ge results in a narrower bandgap.