Interpreting transient photocurrents as a signature of the density of states distribution: the profound importance of the short-time decay

We present a study exploring the fidelity of recovery of the density of states from transient photocurrents for different distributions of traps based on computer simulation of transient photocurrent decay (TPC). The most important result of the work is that much of the information on the form of the density of states (DOS) over an energy range of up to 0.5 eV depth, is contained in the detailed form of the initial decay of the photocurrent on a timescale <10−10 s in which we might expect only the shallowest traps to have an affect. To illustrate this point, we demonstrate that substantially different DOS distributions (exponential, Gaussian, rectangular) can be made to give apparently identical TPC decays over several orders of magnitude of time after an initial trapping phase in which there are only small differences in the shape of the response. Recombination effects may also be included. Nevertheless, using a Fourier transform TPC analytical method we can make a distinction between such DOS distributions, provided the short-time initial decay is included.