Surface photovoltage (SPV) spectroscopy measures the change in a material's surface potential when light strikes it. That change exists only if photogenerated electrons and holes separate and move apart, which makes SPV one of the most direct probes of charge separation available to photocatalysis research.
When a semiconductor absorbs photons, electron-hole pairs form. In the space-charge region near the surface, the built-in field drives the two carriers in opposite directions; the resulting redistribution of charge shifts the surface potential by microvolts to volts. The sign of the SPV signal encodes the direction of charge migration toward or away from the surface, and its magnitude reflects how much charge separates and survives.
Scanning wavelength yields an SPV spectrum with a threshold near the band gap, sub-gap features from defect states, and intensity behavior that separates band-to-band from trap-mediated transitions. Comparing spectra before and after modifications, doping, heterojunction formation, cocatalyst loading, shows whether the change helped or hurt separation.
Photovoltage arises from charge separation, but measured signals can also include thermoelectric artifacts from heating, photoemission contributions and capacitive coupling from the measurement geometry. Chopped-light protocols with phase-sensitive detection separate true photovoltage from these artifacts, and control measurements on reference samples keep interpretations honest.
SPV reports separation capability, not catalytic activity: a material can separate charges beautifully and still fail to use them for chemistry. SPV data are strongest when paired with transient measurements and with actual activity testing.
Perfectlight's surface photovoltage systems support steady-state and transient SPV; see mechanism research solutions.
