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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.

In this study, numerical simulations were utilized to model the optical performance of the perovskite intermediate band solar cells with dispersed quantum dots. Two quantum dots materials were investigated: PbS and Ge. In addition, three volumetric concentrations of the quantum dots were modeled and analyzed. It was concluded that PbS outperformed Ge. Additionally, as the volumetric concentration of the QDs increased, the absorption increased as well.

The optical absorption and the short circuit current of CdTe thin film solar cells have been improved by incorporating arrays of nanostructures in the gold back contact/reflector layer. In this study, three different nano pillar heights, 100, 200 nm, and 300 nm with two periodicities, were investigated. ANSYS HFSS wave optics simulation software was utilized. An increase of 10% in short circuit current density is achieved comparing to the planar cell of an equivalent thickness. Further enhanced performance of CdTe solar cells is expected by incorporating such optimized nanostructure arrays of different sizes and shapes.