Contactless Optical Probing of Photovoltage in Metal‐Insulator‐Semiconductor Electrodes via MV 2 + /MV + Redox Transition Using Second Harmonic Generation
Year: 2026
Type: article
Abstract: ABSTRACT We investigate the photovoltage of n‐Si/5nm Al 2 O 3 /7nm Au electrodes using potential‐dependent second harmonic generation (SHG) in methyl viologen (MV) solutions. For planar 50 nm‐thick Au electrodes immersed in MV‐containing solutions, the SHG intensity exhibits a pronounced suppression near −0.65 V vs. Ag/AgCl. The observed SHG suppression is attributed to the reduction of MV 2+ to the radical cation MV + , which has a 4× higher absorption at 400 nm and 7× higher absorption at 800 nm—leading to decreased SHG intensity. This sharp, voltage‐triggered optical response provides a direct signature of the local surface potential. By correlating the SHG suppression with the applied electrode potential, we demonstrate that the SHG signal can serve as a sensitive, contactless probe of the local surface potential at electrified interfaces. This method is used to probe the photovoltage of n‐Si/5nm Al 2 O 3 /7nm Au electrodes. Without UV excitation, the pronounced suppression begins at −1.2 V vs. Ag/AgCl, unlike on planar Au, due to band bending and leakage resistance. With UV excitation, there is a blue shift in the suppression potential due to the photo‐induced voltage. This approach offers a promising strategy for non‐invasive measurement of photovoltage in MIS electrodes without functionalizing the surface with electric field‐sensitive molecules like 4‐mercaptobenzonitrile.
Source: Small
DOI: 10.1002/smll.76171
Institution: University of Southern California
Language: English
Subfield: Atomic and Molecular Physics, and Optics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: bronze
OpenAlex ID: W7225002250