Generalized analysis of the illumination intensity vs. open-circuit voltage of solar cells

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 V_oc measurements (QssV_oc). 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 QssV_oc measurements and the true steady-state and dark I-V curves. An important application of the QssV_oc technique is to determine the minority carrier lifetime, and the new model proves to be especially important to do this accurately.