Photothermal deflection method for monitoring photoelectronic and nonradiative energy conversion in semiconductor photoelectrochemical cells

By employing an extended model for heat generation in a photoelectrochemical (PEC) cell, an expression for the photothermal deflection (PD) signal at the working electrode of a PEC cell is developed. Furthermore, several experimental PD-signal–versus–bias-voltage curves are presented for three low-resistivity CdS–polysulfide-electrolyte PEC cells. The experimental PD-signal–versus–bias data are then used to obtain the photocurrent quantum efficiencies of the PEC cells at reverse bias and electronic energy-level parameters of the photoelectrochemical interface, making use of a simple, theoretical relationship between the slope of the PD-bias curve and the quantum efficiency; the quantum efficiencies were found to lie within the range 0.05–0.45, reasonable values given that the crystals were found to form current-inhibiting corrosion layers at reverse bias. A general discussion regarding the usefulness of the PD technique in obtaining quantitative PEC energy-conversion parameters is also included, with special emphasis on photogenerated species gradient perturbations.