Composition Engineering in CsPb_1-x Ge _x Br₃ Perovskite Light-Emitting Diodes for Stable and Efficient Performance

Highly luminescent germanium-lead (Ge-Pb) perovskite device with good quantum efficiency was reported recently through tuning the optimal concentration of germanium. However, few theoretical investigations have studied the composition engineering in Ge-Pb-based CsPb1-x Ge x Br3 perovskites and the unique effect of Ge atoms on their optoelectronic properties. In this work, we investigated the structural evolution and optoelectronic properties of the CsPb1-x Ge x Br3 system using first-principles calculations. The result is that all lattice constants and band gaps of different space groups nearly follow a linear trend with increasing Ge atom ratios, except for the most stable P1 phase. More importantly, the modulation mechanism of band gap and the strength of antibonding coupling induced by Ge atoms were proposed to unravel the unusual effect of nontoxic Ge on structural and optoelectronic properties. In addition, spin-orbit coupling and Heyd-Scuseria-Ernzerhof hybrid functional (HSE06) methods were employed to further verify the band structures of three typical systems, including CsPbI3, CsGeBr3, and CsPb0.5Ge0.5Br3. Therefore, our work provides a fundamental understanding of the structural evolution of different phases and the changing trend of electronic properties of CsPb1-x Ge x Br3 perovskites with varying concentrations of Ge atoms, which provides an insightful strategy for designing perovskite optoelectronic devices with superior performance.