Drift-mobility characterization of silicon thin-film solar cells using photocapacitance

We have applied the photocapacitance method to the measurements of hole drift-mobilities in silicon solar cells. We found a simple analysis that yields drift-mobilities even in the presence of anomalously dispersive transport. On one thick sample we measured the hole drift-mobility using both the photocapacitance and the time-of-flight methods; the two methods gave results that were consistent with each other and with the established bandtail multiple-trapping model. We then applied the method to thinner samples that are more characteristic of the conditions in solar modules, but are not generally usable for the time-of-flight method. These samples showed much smaller hole drift-mobilities than expected from the bandtail trapping model. We speculate that the hole drift-mobility has smaller values in regions close to the substrate during deposition than has been reported for thicker samples.