Accurate series resistance measurement of solar cells

The series resistance (R_s) of a solar cell is commonly represented as a constant resistance value. However, because of the distributed nature of series resistance, the effective lumped R_s vary with current density and illumination intensity. Treating R_s as a constant is usually insufficient for an accurate analysis of its J-V curve. This work first presents a review of the distributed nature of series resistance and commonly applied methods to measure R_s. Particular attention is given to the multi-light method (MLM) and it is discussed in detail, where R _s in both the light and dark can be measured as a function of current by extracting R_s from a set of current-voltage (J-V) curves attained at different illumination intensities. The principle behind this method is discussed, and the results are then compared with those of other known methods of R_s measurement. The accurate measurement of R_s(J) attained with the MLM permits the extraction of an R_s-corrected J-V curve, which is theoretically more accurate than that attained by alternative methods because of negligible error from injection dependence and spectral mismatch. With the solar cell equation modified to include R_s(J), we attain a much better fit to experimental data, finding a significant reduction in error compared with using a constant R_s.