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Photocurrent transients have been measured with better than 1 nanosecond time resolution in photoelectrochemical cells with insulator and semiconductor electrodes. The shape of the transients observed with semiconductor electrodes in the time window of several nanoseconds can be deduced from a simple equivalent circuit. The transient observed in the external circuit consists of two contributions, the first is the time integral and the second is directly proportional to the actual photoresponse. At low light intensity good semiconductor electrodes show only the first contribution. There is no direct influence of charge carrier discharge or of the Helmholtz‐layer as such on the fast transient in the nano‐second range.

Escape from the potential well: Competition between long jumps and long waiting timesThe irreversible escape of charge carriers from the bottom of a Coulombic potential well over the barrier by diffusional motion has been measured, for the first time, directly as a rise time of I ns time-resolved current transients in anthracene single crystals with electrolytic contacts. The observed steep decrease in the characteristic escape time down to I ns, with rising electric field up to I X IO j V cm -I, is in excellent agreement with the predictions of a stationary one-dimensional charge carrier injection model with generalized boundary conditions. The electric field dependence of the rate constant for escape cannot be approximated simply by an exponential dependence on the barrier height, as in the familiar Schottky correction for the case of electron emission or in the Poole-Frenkel formula for change carrier escape from a charged trap. As a side result, the hole mobility in the c' direction of anthracene single crystals has been found constant If. =0.85±0.05 cm' Vs·· 1 up to an electric field strength of 5±lO j Vcm-I at room temperature.

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