Surface Donor-Acceptor Dipole Coupling for Enhanced Conductance and Photoresponse in SnO₂ Semiconductor

Tin dioxide (SnO₂) has achieved commercial success in gas sensing and holds significant potential in energy storage and photocatalysis. However, its practical performance is limited by issues such as low intrinsic conductivity, rapid recombination of photogenerated carriers, and narrow spectral response range. To address these challenges, this study proposes a surface donor-acceptor dipole coupling enhancement strategy based on an electron relay. By modifying the SnO₂ surface with highly redox-active viologen units (PV^{2 +}/PV⁰, PV = phenyl viologen, where "P" denotes the phenyl group and "V" denotes the viologen cation), an interfacial dipole coupling is established to form a charge transfer complex (CTC), thereby non-invasively and synergistically improving the overall performance of SnO₂ under mild conditions. The results demonstrate that this strategy significantly optimizes the optoelectronic properties of SnO₂: conductivity increases by approximately 38 times (PV^{2 +}) and 14 times (PV⁰), responsivity to 375 nm ultraviolet light is enhanced by 82 and 37 times, respectively, and the photoresponse is broadened from ultraviolet to near-infrared (up to 760 nm and 1000 nm), greatly improving solar light capture and utilization efficiency. This work provides a new approach to optimizing SnO₂ performance and complements existing methods, promoting its applications in sensing, energy storage, and photocatalysis.