Effect of spatial variation of incident radiation on spectral response of a large area silicon solar cell and the cell parameters determined from it

Effect of spatial variation of incident monochromatic light on spectral response of an n+–p–p+ silicon solar cell and determination of diffusion length of minority carriers (Lb) in the base region and the thickness of the apparent dead layer (xd) in the n+ emitter from the spectral response have been investigated. Spectral response of a few 10 cm diameter and 10×10 cm2 pseudo-square silicon solar cells was measured with the help of a standard silicon solar cell of 2×2 cm2 area in 400–1100 nm wavelength range. Different areas (4, 9, 16, 25 and total area 78.6 or 96 cm2) were exposed. The effect of the radial variation of incident radiation was determined quantitatively by defining a parameter f1 as the ratio of the average intensity falling on the reference cell to that on the exposed area of the test cell. The value of f1 varied between 1 and 1.15 (1.25) as the exposed area of the cell varied from 4 cm2 to 78.6 (96) cm2 indicating that the spatial inhomogeneity of intensity increased with the increase in the exposed cell area. Short-circuit current densities, Jsc, computed from spectral response data for AM1.5 spectrum were less compared to the directly measured values by a factor which was nearly equal to f1. However, radial variation of intensity does not affect the determination of diffusion length of minority carriers in the base region (by the long wavelength spectral response, LWSR method using the measured spectral response data in 0.85<λ<1.05 μm range) and the thickness of the dead layer (by the method of Singh et al. using the data of 0.45<λ<0.65 μm range) significantly.