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.

中文翻译：

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GeSe：Van der Waals太阳吸收体的光谱学和理论研究。

范德华材料GeSe是一种潜在的太阳能吸收剂，但其光电特性尚未得到充分了解。在这里，通过理论和实验相结合的方法，确定了GeSe的光电和结构特性。在室温下发现的基本吸收起始值为1.30 eV，与此前根据Shockley-Queisser详细平衡极限得出的最佳值接近，这与先前报道的1.10 eV的间接基本跃迁相反。所测得的吸收光谱和状态的第一原理联合密度是相互一致的，两者在基本吸收边缘之上均表现出约0.3 eV的额外明显起始。随着理论水平和相应计算成本的增加，从第一性原理计算获得的带隙值收敛到1。来自拟粒子自洽GW方法的33 eV，包括Bethe-Salpeter方程的解。这与从与温度有关的光吸收测量值确定的0 K值一致。与以前的报告相比，基于混合功能的松弛结构揭示了直接的基本过渡。GeSe的光电特性可以通过描述为具有1.30 eV室温带隙的直接半导体的系统来解析。实验与理论之间的高度共识鼓励将这种计算方法应用于其他范德华材料。与以前的报告相比，基于混合功能的松弛结构揭示了直接的基本过渡。GeSe的光电特性可以通过描述为具有1.30 eV室温带隙的直接半导体的系统来解析。实验与理论之间的高度共识鼓励将这种计算方法应用于其他范德华材料。与以前的报告相比，基于混合功能的松弛结构揭示了直接的基本过渡。GeSe的光电特性可以通过描述为具有1.30 eV室温带隙的直接半导体的系统来解析。实验与理论之间的高度共识鼓励将这种计算方法应用于其他范德华材料。