Monitoring photovoltages produced at semiconductor/liquid interfaces using in situ surface-enhanced Raman scattering (SERS) spectroscopy

Abstract

We present optical measurements of photovoltages produced at semiconductor/liquid interfaces using in situ surface-enhanced Raman scattering (SERS) spectroscopy. This SERS-based method employs mercaptobenzonitrile (MBN) as a surface reporter molecule on a p-type indium phosphide (InP) photoelectrode, leveraging the vibrational Stark effect to detect local electric field variations at the electrode/electrolyte interface. Increasing the laser power from 7.7 μW to 800 μW produces a photoinduced shift in the CN stretch Raman mode Δω_CN up to 5 cm⁻¹, corresponding to a photovoltage of 0.4 V produced at the semiconductor/liquid junction. A comparison is made with conventional photovoltage measurements obtained by measuring the shift in the onset potential of the semiconductor photoelectrodes under illuminated and dark conditions. While the conventional photovoltage measurement approach is only valid at very reducing potentials with the semiconductor in deep depletion, this SERS-based approach enables measurement of the photovoltage produced within the semiconductor over the full range of electrochemical potentials. Fundamentally, this reveals how minority and majority carriers in semiconductors reach equilibrium with the redox potential in the electrolyte under illumination.