High Photovoltaic Efficiency in Bulk-Stacked One-Dimensional GeSe$_{2}$ van der Waals Crystal

TL;DR

This study demonstrates that bulk-stacked type-II GeSe2 exhibits high photovoltaic efficiency (~25.6%) due to strong visible-light absorption, with stability confirmed through phonon and molecular dynamics analyses, making it promising for thin-film solar cells.

Contribution

First-principles calculations reveal the photovoltaic potential and stability of bulk-stacked GeSe2, highlighting its advantages over typical 2D van der Waals materials.

Findings

Type-II GeSe2 has a maximum efficiency of ~25.6%.

Type-II is dynamically stable, unlike type-I.

Strong visible-light absorption enhances photovoltaic potential.

Abstract

Germanium diselenide (GeSe$_{2}$) has recently attracted substantial interest as a rare example of one-dimensional (1D) van der Waals material. Here, we investigate the photovoltaic potential of bulk-stacked GeSe$_{2}$ chains using first-principles calculations within the $GW0$ approximation and the Bethe-Salpeter equation (BSE) to capture quasiparticle and excitonic effects. The bulk GeSe$_{2}$ 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 $\mu$m 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.