Bulk nano-heterojunction strategy enables record charge collection in solution-processed metal oxide UV photodetectors

Abstract

Precise control over charge separation, transport, and recombination at nanoscale heterointerfaces is paramount for efficient optoelectronic devices. While scalable solution processing is desirable, achieving both a large interfacial area and low defect density simultaneously remains a significant challenge for metal oxide nanocrystals. Conventional planar solution-processed ZnO/NiO photodetectors, for example, suffer from limited interface areas and short carrier diffusion lengths. Here, we introduce using a novel bulk nano-heterojunction (BNH) architecture as a powerful interface engineering strategy for solution-processed metal oxide nanocrystals. Fabricated entirely via a facile all-solution process, this BNH forms a spatially extended interpenetrating network, creating a vast, low-defect nanoscale heterointerface. Our comprehensive analysis, supported by device simulations, reveals that this BNH architecture creates a superior electronic interface with a quantitatively lower trap density and a favorable cascade-like energy alignment. This structure fundamentally alters charge dynamics by suppressing recombination and dramatically extending the carrier lifetime, enabling unprecedented charge collection. Applied to UV photodetectors, it enables excellent performance for solution-processed ZnO/NiO devices, significantly outperforming planar devices (e.g., >1.8-fold EQE enhancement, 88% responsivity increase, and 5-fold on/off ratio). Notably, EQE exceeds 10 000% at −1 V. This BNH architecture is a versatile platform for optimizing charge collection in solution-processed metal oxide optoelectronics, offering a new paradigm for scalable, high-performance devices.