Band gap modulation via interlayer twist angle in semiconductor hydrogenated borophene

Borophene is a compelling 2D material known for its considerable structural diversity, and its lack of a band gap can be overcome by synthesis of hydrogenated borophene, also known as borophane. However, with the realization of semiconductor borophane polymorphs, understanding the mechanisms controlling their band gaps is fundamental, particularly in vertically stacked architectures, where the role of interlayer coupling must be fully elucidated. Here, we investigate the electronic properties of semiconductor borophane bilayers in different stacking arrangements using density functional theory calculations. Our results show weak interlayer binding, with minor effects on bond lengths, low exfoliation energies, and little charge redistribution. In contrast, interlayer coupling of electron states plays an important role in band gaps, mainly by modifying the conduction bands, an effect strongly influenced by the stacking configuration. The linear optical response also depends on the interlayer twist angle and is strongly affected by excitonic effects in this material. These findings establish a fundamental framework for band gap engineering in borophene-based architectures, paving the way for their integration into next-generation nanoelectronic and optoelectronic devices.