Probing the Interfacial Mechanism of High‐Performance CuInP 2 S 6 /MoS 2 Visible‐Light Photodetectors

Abstract Van der Waals ferroelectrics/semiconductor heterostructures such as CuInP 2 S 6 (CIPS)/ MoS 2 hold promise for optoelectronics, yet their interfacial mechanisms remain poorly understood. Here, it is shown that type‐II band alignment at the CIPS/MoS 2 interface not ferroelectric polarization drives high performance. The gate‐free devices achieve a photocurrent‐to‐dark current ratio >10 4 , 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/MoS 2 devices and offer guidance for interface engineering in 2D optoelectronic devices.