Nonlinear shunt paths in thin-film CdTe solar cells

Abstract

Here we report on a nonlinear, sometimes metastable, shunt-path loss mechanism located at thin-film (TF) solar cell corners, and presumably to a lesser degree, edges that causes much of the degradation in performance during stress testing. We use dark I–V curves and current transients to study the voltage switching behavior for normal, undegraded cells, and degraded cells with these shunt paths that are devastating to performance. By physically removing the microshunt-path defect, located with infrared imaging, and knowing the light and dark I–V performance before and after its removal, we can model the electrical properties of that defect and demonstrate how it so severely compromises device performance. Using a one-dimensional model to describe such cell degradation is inappropriate and misleading. We propose a defect mechanism and discuss the implications for scribe lines and cell ends in full size modules.