Visible-Light-Enhanced NO2 Sensing Based on the Hybrid Orthorhombic/Monoclinic-PdSe2 Nanostructures

Palladium diselenide (PdSe2), as a member of two-dimensional dichalcogenides, has a puckered pentagonal structure and tends to exhibit distinct physical properties due to the various polymorphic phases. In contrast to conventionally orthorhombic PdSe2 (O-PdSe2), the fabrication of continuous metastable monoclinic PdSe2 (M-PdSe2) remains a challenge. Here, we report the polymorphic integration of orthorhombic and monoclinic PdSe2 crystals by concisely controlled selenization engineering under Se-sufficient and Se-deficient growth conditions. Thus, the hybrid O-PdSe2/M-PdSe2 (O/M-PdSe2) nanostructures were fabricated for the first time. We found that the O/M-PdSe2 nanostructures may be used as the broadband photodetector with a relatively high responsivity of 211.4 mA W–1, laying the foundation for the expansion of high-performance photoexcited gas sensors operating at room temperature. The O/M-PdSe2 sensor exhibited extremely fast response and recovery times (132/84 s) toward 10 ppm NO2 gas under 405 nm light illumination compared to the dark condition. In addition, according to the optical absorption spectra and ultraviolet photoemission spectroscopy analyses, the energy band alignment at the O/M-PdSe2 interface was determined, and the detailed gas-sensing mechanism was also proposed on this basis. This work realizes the continuous fabrication of the hybrid O/M-PdSe2 nanostructures with promisingly combined photoelectric and gas-electric properties, which may promote the development of high-performance multifunctional nanoelectronic devices to meet the global challenges of energy shortage and environmental protection.