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A new technique to determine the current–voltage characteristics of solar cells based on simultaneously measuring the open-circuit voltage as a function of a slowly varying light intensity has been proposed recently [Sinton and Cuevas, Proc. 16th European Photovoltaic Solar Energy Conf., Glasgow, UK, May 2000, pp. 1152–1155]. This paper presents a detailed theoretical analysis and interpretation of such quasi-steady-state Voc measurements (QssVoc). The ability of this analysis to accurately obtain the true steady-state device characteristics even in the case of high lifetime, high resistivity devices is demonstrated experimentally. Besides reasonable choices for the light source (2 and 4 ms exponential flashes), we have also used a rapidly varying illumination (0.35 ms decay rate) to illustrate problems with the existing analysis. The new analysis results in an excellent agreement between the three QssVoc measurements and the true steady-state and dark I–V curves. An important application of the QssVoc technique is to determine the minority carrier lifetime, and the new model proves to be especially important to do this accurately. |
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