Field‐Aligned Photovoltaic‐Photothermoelectric Coupling in SnSe/ZnO/Si Heterojunctions for Stable Self‐Powered Broadband Photodetection

ABSTRACT Broadband self‐powered photodetectors that combine photovoltaic (PV) and photothermoelectric (PTE) effects are attractive for low‐power optoelectronic sensing. However, in many heterojunction devices, the PV built‐in field and the PTE‐induced field point in opposite directions, causing wavelength‐dependent polarity reversal and unstable signal readout. Here, we report a field‐aligned p‐SnSe/n‐ZnO/p‐Si heterojunction that converts the conventional competition between PV and PTE effects into constructive coupling. Comparative p‐SnSe/n‐Si, p‐SnSe/n‐ZnO/n‐Si, and p‐SnSe/n‐ZnO/p‐Si devices were fabricated to clarify the roles of the ZnO interlayer and the Si conductivity type. Experiments and finite‐element simulations indicate that ZnO improves carrier extraction and interfacial charge transport, whereas p‐type Si reconfigures the dominant internal electric field and suppresses polarity reversal. The optimized p‐SnSe/n‐ZnO/p‐Si device therefore delivers stable unipolar photovoltage generation over 330‐1550 nm under zero bias. It achieves a voltage responsivity of 558.5 V W −1 and a specific detectivity of 1.56 × 10 13 Jones at 330 nm under 0.21 mW cm −2 illumination, while maintaining good cycling and ambient‐storage stability. A proof‐of‐concept ASCII optical‐signal decoding demonstration further verifies its potential for self‐powered optical communication. This work provides an electric‐field‐alignment strategy for regulating PV‐PTE coupling and offers a practical route toward stable broadband self‐powered photodetectors.