Thickness- tuned band engineering for efficient photodetection in 2D CuInP2Se6

The combination of unique narrow bandgap electronic and optical properties, along with van der Waals surfaces in 2D materials, makes this class of materials highly promising for advancing photodetectors. In this study, we employ first-principles calculations to investigate the structural, electronic, and vibrational properties of the 2D CuInP₂Se₆ van der Waals material. Theoretical studies reveal phase-dependent properties in CuInP₂Se₆, including bulk paraelectric, bulk ferroelectric, and monolayer paraelectric phases. Notably, the material exhibits a tunable electronic band structure through phase transitions and layer thickness modulation. Among the explored phases, the paraelectric monolayer demonstrates a strong second harmonic generation response while also displaying lower thermal conductivity, making it suitable for nonlinear optical applications. The theoretically predicted optical properties were validated experimentally by synthesizing CuInP₂Se₆ using multi-step solid-state and chemical vapor transport reactions. A fabricated photodevice, configured as Au/CuInP₂Se₆/SiO₂ via standard optical lithography, exhibited UV–visible photodetection with a maximum photoresponsivity at 405 nm. Similarly, a modelled photodevice with the same configuration also demonstrated photodetection, attaining a maximum photoresponsivity at 405 nm. Furthermore, encapsulating silicene is expected to further modulate the electronic band structure and enhance photodetection performance, paving the way for future advancements in integrated UV–Vis-NIR optoelectronic devices. The significant improvement in photoconductive gain in the NIR range is attributed to an efficient charge transport pathway and interfacial encapsulation.