Enhancing Electrical and Optoelectronic Properties of ZnO via Interfacial Charge Transfer with Strong Electron Donors

Abstract

Zinc oxide (ZnO) semiconductors have emerged as core materials for constructing efficient electron transport layers in photovoltaic devices and exhibit broad application prospects in photodetection, photocatalysis, and sensors materials. Nevertheless, their intrinsic limitations-including insufficient intrinsic conductivity, inefficient charge separation, and a narrow spectral response (<400 nm)-remain major obstacles to achieving high conversion efficiencies in optoelectronic devices across these fields. To address these challenges, we developed a novel strategy that utilizes interfacial charge transfer with strong electron donors to simultaneously enhance the electrical and optoelectronic properties of ZnO. By constructing a stable donor-acceptor (D-A) interface on the ZnO surface, a charge transfer complex (CTC) is formed, enabling synergistic modulation of its electronic and optoelectronic characteristics. Monosubstituted viologen radicals (PQ ^• ), featuring multiple reversible redox states and strong electron-mediating capability, markedly enhance carrier separation and broaden the spectral response range in ZnO, resulting in a 460-fold increase in conductivity. The photoresponse cutoff is simultaneously extended from the ultraviolet to 808 nm, and the responsivity is concurrently enhanced by two orders of magnitude at 520, 635, 730, and 808 nm, enabling full visible-spectrum detection. Transient absorption spectroscopy directly reveals the formation of long-lived charge-separated states (τ = 201 ps). This work provides a mild and efficient strategy for improving the electrical and optoelectronic performance of ZnO while avoiding the introduction of deep-level defects or the construction of complex heterostructures.