Transparent and Photovoltaic Water–Semiconductor Interface for Ultra‐Low‐Light Omnidirectional Photodetection

Sustainable energy efforts demand self‐powered photodetectors (PDs) that operate without an external bias. Conventional PDs typically rely on solid‐state Schottky or p/n junctions formed through complex growth techniques and fixed, rigid structures. Here, to develop a self‐powered PDs, we present a novel approach that leverages a static water–ZnO interface to form a Schottky‐like junction on a flexible substrate. Two device configurations are developed—a water droplet system and a continuous water system—which exhibit excellent photodetection performance. Under ultralow light intensities (down to 10 nW cm ⁻² ), the devices generate photocurrents ranging from 1.5 to 115 μA cm ⁻² and deliver open‐circuit voltages of up to 0.2 V. Moreover, the devices offer omnidirectional (360°) light detection and maintain stable photodetection performance after multiple bending cycles at a bending radius of 0.5 cm. These results demonstrate that water–semiconductor interfaces provide a simple yet effective path towards flexible, transparent, photovoltaic and self‐powered PDs with high sensitivity under ultralow light conditions.