Transient photocurrent spectroscopy on amorphous silicon solar cells

Transient photocurrent response measurements have been used to characterize deep level impurities in amorphous silicon solar cells. These measurements are based on the analysis of the current deficiency and the overshoot in the photocurrent transients of a solar cell at the onset of an irradiation pulse as a function of the preceding dark time interval. The current deficiency is a measure for the carriers emitted from traps during the preceding dark time. Variation of temperature changes the reemission probability from traps, a decrease of irradiation wavelength reduces the generation depth of photocarriers within the i layer, electric bias voltage changes the electric field in the i layer. Thus the influence of the density of states, the homogeneity of carrier generation, and the electric field on the photocurrent onset behavior can be observed. The contribution of a higher density of states in the mobility gap to the photocurrent transients after light degradation of the sample is examined. To receive more information about the density of states in amorphous silicon solar cells the authors compare their measurements with photocurrent modeling results