ANALYSIS OF TIME-RESOLVED PHOTOCURRENT TRANSIENTS AT SEMICONDUCTOR LIQUID INTERFACES

Small signal photocurrent transients have been measured for n-Si/CH3OH -Me2Fc+/0/Pt, n-Si/Au/CH3OH-Me2Fc+/0/Pt, n-Si/Pt/NaOH(aq)/Ni(OH)2/Ni, n-TiO2/NaOH(aq)/Ni(OH)2/Ni, and n-TiO2/NaOH(aq)-Fe(CN)63-/4-/Pt cells. Even though the radio-frequency and microwave conductivity signals fo r photoexcited n-Si/CH3OH-Me2Fc+/0 contacts persist for > 100 mus, the photocurrent transients for these interfaces decayed in <10 mus and w ere limited by the series resistance of the cell in combination with t he space-charge capacitance of the semiconductor. An equivalent circui t model is presented and physically justified in order to explain this behavior. The model is also used to elucidate the conditions under wh ich photocurrent transients at semiconductor electrodes can be expecte d to yield information regarding the faradaic charge-transfer rate acr oss the semiconductor/liquid interface.