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

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 $μ$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.

Figures (4)

• Figure 1: (Color online) Atomic configurations of (a,b) type-I bulk GeSe$_{2}$ and (d,e) type-II bulk GeSe$_{2}$. Triclinic primitive unit cells and corresponding lattice vectors $\mathbf{a}_{1}$ (red), $\mathbf{a}_{2}$ (green) and $\mathbf{a}_{3}$ (blue) are illustrated with atomic chains. Corresponding irreducible Brillouin zones (IBZ) are illustrated for (c) type-I and (f) type-II chains. Reciprocal lattice vectors $\{\mathbf{b}_{1}, \mathbf{b}_{2}, \mathbf{b}_{3}\}$ and high-symmetric points are displayed together. Atomic configurations are drawn by using VESTA Momma:db5098.
• Figure 2: Electronic structure of bulk type-I and type-II GeSe$_{2}$. Electronic band structures computed by DFT-GGA (blue dashed) and $GW$ (red solid) approximations for (a) type-I bulk GeSe$_{2}$ and (b) type-II bulk GeSe$_{2}$. Absorption spectra $\varepsilon_{2}$ from $GW$ + BSE (magenta dashed) and $GW$ + RPA (red solid ) for (c) type-I bulk GeSe$_{2}$ and (d) type-II bulk GeSe$_{2}$.
• Figure 3: Absorption coefficients (red solid line) of (a) type-I and (b) type-II bulk GeSe$_{2}$. The solar irradiance spectra, Air Mass 1.5, is shown with gray lines. The gray box specifies the energy range of visible light. The SLME $\eta$ of (c) type-1 and (d) type-2 bulk GeSe$_{2}$ are drawn as a function of thickness. For thickness 0.5 $\mu$m, the values of SLME are explicitly indicated.
• Figure 4: Phonon frequencies of (a) type-I and (b) type-II bulk GeSe$_{2}$. (c) Total potential energy and temperature as a function of time during canonical MD simulations at 300 K. (d) The final structure at the end of the simulation time of 4 ps (inset).