Impact of Nonuniform Illumination and Probe Bar Shading on Solar Cell I–V Measurement

Abstract

This paper examines the effect of nonuniform and probe-bar-shaded solar illumination in the I–V characterization of large area Si wafer solar cells. The illumination conditions were experimentally implemented by masking the solar cell during measurement. The results are examined in detail with simulations in Griddler, a finite element analysis software developed at the Solar Energy Research Institute of Singapore. The light I–V characteristics, particularly the fill factor, depend on the specific irradiance profiles relative to the current-collecting busbars due to effects on the effective series resistance Rs. The effect is slight for small light nonuniformities (IEC 60904 Class A nonuniformity classification or <2%) but for light nonuniformities up to 20%, the standard deviation in the fill factor can reach about 0.19% absolute. Probe bar shading directly leads to an underestimation of the measured fill factor due to longer current paths and larger voltage drops.