High photovoltaic efficiency in bulk-stacked one-dimensional GeSe2 van der Waals crystal

Abstract

Germanium diselenide (GeSe₂) has recently 2attracted substantial interest as a rare example of a one-dimensional (1D) van der Waals material. Here, we investigate the photovoltaic potential of bulk-stacked GeSe₂ chains using first-principles calculations within the GW₀ approximation and the Bethe–Salpeter equation (BSE) to capture quasiparticle and excitonic effects. The bulk GeSe₂ exhibits indirect GW band gaps of 1.92 eV (type-I) and 1.08 eV (type-II). Optical calculations show markedly stronger visible-light absorption in type-II, yielding a spectroscopically limited maximum efficiency (SLME) of ∼25.6% at a 0.5 µm thickness. Phonon and room-temperature ab initio molecular dynamics analyses indicate that type-II is dynamically stable, whereas type-I shows imaginary phonon modes, suggesting a propensity for structural distortion. These results identify type-II GeSe₂ as a promising stable absorber for thin-film photovoltaics with enhanced flexibility compared to typical 2D vdW systems.