Fused Nanojunctions of Electron-Depleted ZnO Nanoparticles for Extraordinary Performance in Ultraviolet Detection

Zinc oxide nanoparticles (ZnO-NPs) with radius of the Debye length have the optimal electron depletion effect for high-performance optoelectronic devices. However, a major challenge remains in assembling ZnO-NPs into 3D interlinked networks for high-efficiency electron transport. Here an ultrafast thermal annealing process has been developed by exposing the ZnO-NPs to excessive heat for a short period of 2 s. This enables the formation of NP–NP interface nanojunctions, resulting in nearly two orders of magnitude decrease of the dark current I_Dark and more than an order of magnitude increase of the photocurrent I_Ph under ultraviolet (UV) illumination. Moreover, the UV photodetectors based on such 3D interlinked ZnO-NP networks exhibit extraordinary performance with high I_Ph/I_Dark ratio of 3.1 × 10⁵, responsivity of up to 95.4 A W⁻¹ at 340 nm UV power of 0.1 mW cm⁻² (and up to 430 A W⁻¹ at 0.003 mW cm⁻²), detectivity of 1.4 × 10¹³ Jones, and rise/decay time of 9.4 s/13.5 s. These results illustrate the critical importance of the NP–NP interface nanojunctions and provide a low-cost pathway for high-performance ZnO-NP optoelectronics.