Thin-Layer NbOCl₂ Flat-Band Semiconductor for Efficient PEC Photodetection

Emerging two-dimensional semiconductor materials are of considerable interest for optoelectronic applications because of their unique charge-transport and photoresponse properties. Among them, NbOCl₂ demonstrates great potential for optoelectronic device applications due to its exceptional electrical transport properties and ultrafast optical response. In this work, we successfully fabricated photoelectrochemical (PEC) NbOCl₂ photodetectors with controllable thickness via liquid-phase exfoliation and systematically investigated the effect of the nanosheet thickness on device performance. Notably, the results show that the photodetection behavior can be effectively tuned by varying the thickness of the NbOCl₂ nanosheets. Under simulated sunlight, the PEC-type photodetector based on NbOCl₂ nanosheets exhibits a rapid optical response of 0.09 s, an approximately 243-fold increase in photocurrent at an applied bias of 1 V, and an excellent cycling stability. Density functional theory calculations reveal that the enhanced performance originates from efficient electron-hole separation and flat-band-induced interband transitions, which facilitate charge transport and carrier generation. These results demonstrate that thin-layer NbOCl₂ is a promising candidate for high-performance PEC photodetectors and related optoelectronic devices.