Accelerated Light-Induced Degradation (ALID) for Monitoring of Defects in PV Silicon Wafers and Solar Cells

Abstract

In crystalline silicon, above-bandgap illumination can transform defects into strong recombination centers, degrading minority-carrier lifetime and solar cell efficiency. This light-induced degradation (LID) is due primarily to boron–oxygen and iron–boron defects, and can be reversed using thermal treatments that are distinctly different for each type of defect. Combining illumination and thermal treatment, we have designed an accelerated light-induced degradation (ALID) cycle that, within minutes, transforms defects into the distinct states needed to isolate individual contributions from boron–oxygen dimers (BO_2i) and interstitial iron (Fe_i). In this cycle, the concentrations of BO_2i and Fe_i are determined using surface photovoltage (SPV) diffusion length measurement. The ALID cycle uses reversible defect reactions and gives very good repeatability of wafer-scale mapping of BO_2i and Fe_i in photovoltaic (PV) wafers and final solar cells.