Abstract
We have measured the current-voltage curves of thin-film solar cells using focused laser spots (30-500 /spl mu/m) using DC and modulated (AC) photocurrent techniques. The AC short-circuit current response (I/sub SC/) and the AC fill factors (FF) decrease for small spot sizes corresponding to several 100 sun light intensities. Laser line scans across the devices produced significant but reproducible spatial fluctuations in AC I/sub SC/. These spatial variations depend on spot size and are reduced by scanning with lower light intensity. The reduction of AC FF and AC I/sub SC/ was largest in a-Si:H, intermediate in CdTe and CuInSe/sub 2/ (CIS), barely noticeable in some Cu(Ga,In)Se/sub 2/ (CIGS) cells and absent in a silicon cells. The observations on CIGS and some CIS cells can be explained by internal series resistance, but field dependent collection and recombination effects must be invoked to explain results on most thin-film solar cell materials. Such field modification is not accounted for in standard exponential diode equation models.
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