Pressure-regulated bandgap narrowing and photoelectric activity enhancement in layered halide compound GeI₂

Layered semiconductors offer distinct advantages for optoelectronically responsive heterojunction devices due to their strong light-matter interactions and weak interlayer van der Waals interactions, which enable exfoliation into adjustable thicknesses. However, their practical utility is often restricted by excessively wide bandgaps, which limit spectral response within the visible light range and reduce light absorption efficiency, thereby constraining broadband detection capabilities. In this study, pressure was employed as a tuning parameter to modulate the bandgap and optimize the photoelectric performance of the layered semiconductor GeI₂. Structural stability under moderate compression (5 GPa) was confirmed through in situ Raman spectra and x-ray diffraction, with no evidence of phase transition. At 5 GPa, a remarkable five-order-of-magnitude enhancement in photoelectric activity was observed. In situ UV-visible absorption spectroscopy, supported by theoretical calculations, revealed that this enhancement is primarily driven by pressure-induced narrowing of the bandgap. These findings offer critical insights for designing two-dimensional broadband photodetectors with tailored bandgap properties and enhanced photoelectric response, contributing to advancing next-generation flexible optoelectronic devices.