GeSe: optical spectroscopy and theoretical study of a van der Waals solar absorber
2020
The
van der Waals material GeSe is a potential solar absorber,
but its optoelectronic properties are not yet fully understood. Here,
through a combined theoretical and experimental approach, the optoelectronic
and structural properties of GeSe are determined. A fundamental absorption
onset of 1.30 eV is found at room temperature, close to the optimum
value according to the Shockley–Queisser detailed balance limit,
in contrast to previous reports of an indirect fundamental transition
of 1.10 eV. The measured absorption spectra and first-principles joint
density of states are mutually consistent, both exhibiting an additional
distinct onset ∼0.3 eV above the fundamental absorption edge.
The band gap values obtained from first-principles calculations converge,
as the level of theory and corresponding computational cost increases,
to 1.33 eV from the quasiparticle self-consistent GW method, including
the solution to the Bethe–Salpeter equation. This agrees with
the 0 K value determined from temperature-dependent optical absorption
measurements. Relaxed structures based on hybrid functionals reveal
a direct fundamental transition in contrast to previous reports. The
optoelectronic properties of GeSe are resolved with the system described
as a direct semiconductor with a 1.30 eV room temperature band gap.
The high level of agreement between experiment and theory encourages
the application of this computational methodology to other van der
Waals materials.
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