Light- and Elevated-Temperature-Induced Degradation-Affected Silicon Cells From a Utility-Scale Photovoltaic System Characterized by Deep-Level Transient Spectroscopy

Abstract

Photovoltaic modules from a utility-scale field experienced power loss by light- and elevated-temperature-induced degradation (LeTID). Samples from the affected monocrystalline silicon cells are cored and extracted from the module packaging and then laser-scribed to form 2-mm diameter isolated areas. Using deep-level transient spectroscopy, a majority-carrier, hole-trap defect with an activation energy of 0.42 eV is detected on degraded and regenerated samples. The LeTID-degraded sample, however, has a larger signal corresponding to a trap density of 1.1 &#x00D7; 10¹³ cm^&#x2212;3, which is about five times larger than the 2.1 &#x00D7; 10¹² cm^&#x2212;3 trap density of the regenerated sample. An increase in filling pulse time from 50 <i>&#x03BC;</i>s to 20 ms shows a slight decrease in activation energy from 0.42 to 0.36 eV suggesting that the defect level may consist of a band of energy states where shallower states continue to fill with long filling times. The capture rate of the defect is directly measured using an increasing series of filling pulsewidths in 15 to 125 ns range. This leads to a measured capture cross section of 5.1 &#x00D7; 10^&#x2212;17 cm², and using an approximate defect density of 10¹³ cm^&#x2212;3, the majority-carrier-hole lifetime related to this defect is approximately 100 <i>&#x03BC;</i>s when in the LeTID-degraded state.