Illuminating the cell through the back achieves a higher sensitivity to the back surface recombination than illumination through the front surface. Obviously, the cell has to be bifacially sensitive to permit rear illumination. The quantum efficiency for back illumination is [409, 410]
IQE =———————- A——————– (C.9)
cosh(^/I) + -^-sinh(^os/I)
Here, plotting IQE versus La yields a linear relation. The slope and intercept provide information on Sb and L. Equation (C.9) predicts that the ratio of the slope to the intercept is Sb/Dn; here Dn is the diffusion coefficient of the minority carriers (electrons).
ABSORPTION LENGTH La [jum]
C.3 Effective diffusion lengths (formulas)
