Mitigating Light and Elevated Temperature Induced Degradation in Multicrystalline Silicon Wafers and PERC Solar Cells Using Phosphorus Diffusion Gettering

Abstract

Reducing light and elevated temperature induced degradation (LeTID) is important for the industrial success of PERC (passivated emitter and rear cell) solar cells fabricated on high‐performance multicrystalline silicon (multi‐Si) wafers. Although there has been a lot of progress in understanding the degradation kinetics, the defect(s) responsible for LeTID in multi‐Si wafers at elevated temperatures (≈80 °C, 1 Sun) has yet to be identified. In this study, the authors look at the possibility of using phosphorus diffusion gettering (PDG) for reducing LeTID in multi‐Si wafers and solar cells. By measuring light induced defect concentrations in multi‐Si wafers before and after LeTID, the authors observe that PDG can substantially reduce the average defect concentration. Trace element analysis using inductively coupled plasma mass spectrometry reveals that multi‐Si wafers from the edge of the ingot contain a high concentration of Cu, Ni and Ti in grains that degrade more than neighboring grains. To explore PDG for reducing LeTID in multi‐Si PERC solar cells, the authors fabricate cells with two different emitter profiles. Etching back a heavily diffused emitter to obtain a high sheet resistance is observed to improve the LeTID performance of the solar cells, an effect that is very likely related to a reduced impurity concentration within the wafer.