A NEW METHOD OF DETERMINATION OF MINORITY-CARRIER DIFFUSION LENGTH INTHE BASE REGION OF SILICON SOLAR-CELLS

A new method of determination of the minority carrier diffusion length (L) in the base region of an n(+)-p-p(+) silicon solar cell using the spectral response of the cell in a middle wavelength (lambda) range, e.g., 0.75 < lambda < 0.90 mu m is presented. In this method Q(int) or if required Q(int)/f where Q(int) is the internal quantum efficiency of the cell and f = e(-(xb alpha lambda))(L(2) alpha(lambda)(2)/L(2) a lpha(lambda)(2) - 1), x(b) being the distance of base region from the front surface, is plotted against the reciprocal absorption coefficien t (alpha(lambda)(-1)) of silicon. The Q(int) versus alpha(lambda)(-1) or else Q(int)/f versus alpha(lambda)(-1) plot gives an intercept L(MW ) on the alpha(lambda)(-1)-axis and a unit intercept on the other axis . The intercept length L(MW) is related to L through d/L and S-B, wher e d is the thickness of the base region and S-B is the back surface re combination velocity of minority carriers. For d/L > 2.5, L = L(MW) an d is independent of S-B. However, for d/L < 2.5, the true value of L w hich may be somewhat different from L(MW) can be determined if S-B is known. While most existing long wavelength spectral response (LWSR) me thods require d/L to be large (d/L > 2.5) is such that tanh(d/L) appro ximate to 1, this method has no such restriction on d/L. It is highly suitable for cells for which L is large but x(b) is small. We have app lied the MWSR and LWSR methods to a few n(+)-p-p(+) silicon solar cell s and have found that the former is much superior to the fatter if d/L < 2.5.