Theoretical investigation of FAPbSnGeX efficiency.

The use of hybrid lead halide perovskites as light absorbers in photovoltaic cells have gained large interest due to their optoelectronic properties and high efficiency. However, most hybrid perovskites contain toxic lead which has a negative impact on the environment. In this work, we systematically study the structural, electronic, and optical properties of lower lead halide perovskites FAPbSnGeX (X = I, Br, Cl), as well as discussing their photovoltaic performance (open circuit voltage ( ), the short circuit current density ( ), and the power conversion efficiency ()) using density functional theory (DFT), and we compare these with FAPbX (X = I, Br, Cl) frameworks.

Strain and size combined effects on the GaN band structure: VEELS and DFT study.

A nanoscale study of combined strain/size effects has been performed using monochromated valence electron energy-loss spectroscopy and density functional theory (DFT) calculations to locally explore the valence and conduction bands of a strained 2 nm GaN quantum well inserted between two fully relaxed AlN thick layers. Two main electronic transitions from the valence to the conduction band were experimentally detected and interpreted. The first transition was shown to be a collective oscillation (or plasmon), which was significantly blue-shifted in energy mainly due to the widening of the valence-band top-part.