Spatially Resolved Identification of Shunt Defects in Thin Film Solar Cells via Current Transport Efficiency Imaging Combined with 3D Finite Element Modeling

Inhomogeneously distributed shunt defects significantly reduce the performance of thin film solar cells. The existing uses of simple equivalent circuit models and lumped cell-level parameters are insufficient to understand the behaviors of different shunting types. This study demonstrates how the reciprocity theorem, which bridges the relationship between the terminal differential changes and local responses of a solar cell, for the current transport efficiency can be used to spatially identify ohmic and nonohmic shunt defects exemplified in CdTe solar cells. Differential electroluminescence imaging and three-dimensional finite element modeling are used to determine the current transport efficiency images. Due to the specific local differential conductance behaviors, the application of current transport efficiency imaging for the detailed analysis of different shunt defects is successfully verified in both experimental and simulation methods. In addition, the influences of two types of shunt defects on the electrical potentials and current flow of a cell are discussed. The modeling results indicate that a nonohmic shunt defect with a larger junction voltage dip and leakage current is more detrimental than an ohmic shunt defect within the cell.