Mitigating LeTID in TOPCon solar cells through accelerated DC bias regeneration: Mechanisms and performance recovery

Abstract

This study investigates Light and Elevated Temperature-Induced Degradation (LeTID) in high-efficiency TOPCon solar cells and evaluates electrical regeneration using DC biasing. LeTID was accelerated by exposing cells to 1-sun illumination at 85 °C for 15 h, resulting in a ∼4% reduction in open-circuit voltage (V_oc) and minor declines in J_sc, fill factor (FF), and efficiency (η). External Quantum Efficiency (EQE) spectra revealed significant losses beyond 900 nm, indicating increased bulk recombination from hydrogen-related defect activation. Dark I–V analysis further confirmed elevated forward current and a higher ideality factor, reflecting degraded junction quality. Regeneration was performed under forward and reverse DC bias at 1.0 V. Forward biasing with injection currents of 0.5 A, 1.0 A, and 1.5 A achieved near-complete recovery of V_oc (>99.9% of the initial value) within 7 h, whereas reverse biasing required approximately 9 h for similar restoration. Post-regeneration measurements demonstrated full recovery of key parameters, with normalized V_oc, J_sc, FF, and η reaching 0.9996, 0.9997, 0.9997, and 0.9996, respectively. EQE and dark I–V curves confirmed the restored spectral response and improved diode behaviour, while the series resistance returned to ∼0.75–0.80 Ω cm². These findings confirm that LeTID in TOPCon solar cells is a reversible process and establish forward DC biasing as a rapid, reliable, and scalable regeneration approach.