Photoelectron excitations in oxide heterostructures routinely elicit both surface photovoltage and open-circuit voltage. Surface photovoltage measurements are hence often used as a proxy to gauge open-circuit voltage response. Here, we present a method for studying photovoltaic effects in oxide heterostructures by concurrently measuring, with an atomic force microscope, surface photovoltage $\left(\mathrm{\Delta }{V}_{\mathrm{SPV}}\right)$ and open-circuit voltage $\left(V_{\mathrm{OC}}\right)$ while varying illumination wavelength and intensity. This combined method is applied at super- and subband-gap illumination wavelengths on ${\mathrm{Bi}}_2{\mathrm{FeCrO}}_6/\mathrm{Nb}\text{−}{\mathrm{SrTiO}}_3$ heterostructures annealed under various oxidative and reductive conditions. The results show that $\mathrm{\Delta }{V}_{\mathrm{SPV}}$ consistently reflects interfacial photocarrier generation, whereas $V_{\mathrm{OC}}$ is more governed by photocarrier transport, sensitive to recombination. It is also shown that deep oxygen-vacancy levels act as recombination centers, whereas shallow cation-vacancy levels impact depletion region width. Experimental observations are consistent with DFT density of states of crystals containing isolated and coupled vacancies. Together, $\mathrm{\Delta }{V}_{\mathrm{SPV}}$ and $V_{\mathrm{OC}}$ spectroscopies—applied across multiple excitation energies and intensities—offer valuable insights into mechanisms governing photon-induced electrical power generation in photovoltaic oxide heterostructures.

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• Optoelectronics
• Photoconductivity
• Photovoltaic absorbers
• Photovoltaic effect
• Surface & interfacial phenomena
• Thin-film photovoltaics
• Complex oxides
• Ferroelectrics
• Heterostructures
• Junctions
• Solid-solid interfaces
• Atomic force microscopy
• Photoexcitation