Photocharge Transfer Mediation by Adsorbed Ions: Simulation of Photocurrent-Voltage Curves Based on Results of Photoluminescence Transient Measurements

High surface capture velocities, of the order of 10⁵–10⁶ cm s^-1, for both minority and majority carriers were evaluated by us recently from measurements of photoluminescence decay in the picosecond time domain, taken for n-CdS crystals immersed in alkaline sulfide-polysulfide electrolytes. A resulting question was raised, whether an interface with high surface capture rate constants for both p and e will allow significant conversion efficiencies under normal continuous illumination conditions, as known to be obtained experimentally for this particular interface. This paper presents simulations of current-voltage curves, which demonstrate that J vs. V relations of desirable forms, and of good associated conversion efficiencies, may indeed be obtained in the presence of high surface capture rate constants for both holes and electrons. The condition for such behavior is that the transfer of the photogenerated minority carrier from the surface trap to an acceptor in solution proceeds with a minimum rate constant, typically of the order of 10⁶s^-1. This leads to a conclusion on the possible role of surface states, particularly those derived from adsorbed anions, as mediators of photocharge transfer.