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 for photoexcited n-Si/CH3OH-Me2Fc+/0 contacts persist for > 100 mus, the photocurrent transients for these interfaces decayed in <10 mus and were limited by the series resistance of the cell in combination with the space-charge capacitance of the semiconductor. An equivalent circuit model is presented and physically justified in order to explain this behavior. The model is also used to elucidate the conditions under which photocurrent transients at semiconductor electrodes can be expected to yield information regarding the faradaic charge-transfer rate across the semiconductor/liquid interface.