Diatom-Inspired 3D Hierarchical Liquid Metal Sponge for Flexible Photoelectrochemical Photodetectors

Inspired by the hierarchical micro/nanoscale architecture of diatoms which are renown for capturing and utilizing dim light in oceanic environments, a three-dimensional (3D) hierarchical liquid metal (LM) sponge was proposed for advancing flexible photoelectrochemical (PEC) photodetectors. A room-temperature LM nanodroplet (ND)-bridging strategy by deformable welding LM NDs on polymer fibers was developed to controllably fabricate 3D architectures consisting of LM integrations in the form of interconnected either one-dimensional (1D) liquid-bridges or two-dimensional (2D) liquid-films. Optical characterization reveals that the 3D hierarchical architecture with radian 2D liquid-films (3D-HA-R2DLF) exhibits moderate absorption (0.34), enhanced reflection (0.55), and minimal transmission (0.01) at 500 nm, with light scattering extending the optical path length for improved photon utilization. Carrier dynamics analysis demonstrates its optimal performance: a carrier concentration of 9.79 × 10¹¹ m^-3 and mobility of 9.31 × 10⁶ cm²/V·s, outperforming 1D-liquid-bridges (high mobility but low concentration) and the 3D hierarchical architecture with flat 2D liquid-films (3D-HA-F2DLF) (high concentration but mobility-limited scattering). This 3D architecture combines conductive LM for charge transport with semiconductive amorphous gallium oxide (GaO_x) layers for photoabsorption/conversion, achieving the efficient light energy utilization similar to that done by diatoms' microstructure. Specifically, the 3D LM sponge consisting of radian 2D liquid-films achieved a photocurrent density of 1.99 μA/cm², 3.1 times and 9.47 times higher than its counterparts with flat 2D liquid-films and 1D-liquid-bridges, respectively. Additionally, it exhibited faster response times (0.19 s for response; 0.13 s for recovery). The photodetector demonstrated excellent stability over 4000 s of continuous use and 4000 bending cycles, highlighting its robustness. The concept by bridging LM-NDs into 3D hierarchical and heterogeneous architectures offers a promising strategy to integrating LMs and semiconductors into functional devices, particularly for flexible photoelectric-devices.