Probing the Interfacial Mechanism of High-Performance CuInP₂S₆/MoS₂ Visible-Light Photodetectors

Van der Waals ferroelectrics/semiconductor heterostructures such as CuInP₂S₆ (CIPS)/ MoS₂ hold promise for optoelectronics, yet their interfacial mechanisms remain poorly understood. Here, it is shown that type-II band alignment at the CIPS/MoS₂ interface not ferroelectric polarization drives high performance. The gate-free devices achieve a photocurrent-to-dark current ratio >10⁴, and a responsivity of 730 A·W^-1 under low-intensity visible illumination without pre-poling. Inserting an h-BN spacer to eliminate direct band alignment sharply degrades device performance, confirming its essential role in enabling efficient photocarrier separation. Nanoscale measurements, photoluminescence quenching, bandgap narrowing, and first-principles calculations all consistently support the presence and function of type-II alignment. These results clarify the operating mechanism of CIPS/MoS₂ devices and offer guidance for interface engineering in 2D optoelectronic devices.