Stability of Commercial nc‐Si:H Heterojunction Solar Cells Under Variable Illumination

ABSTRACT Silicon heterojunction (SHJ) solar cells gain market share due to their high efficiency. However, amorphous silicon is thermally unstable, and although nanocrystalline silicon (nc‐Si) enhances efficiency, its extended stability trends remain unclear, especially following high‐intensity illuminated annealing. This study investigates the stability of nc‐Si SHJ cells, precursors, and symmetrical structures under light soaking (LS) and dark storage over 1200 h. High‐intensity treatment improves initial cell efficiency by 0.3% abs , driven by increases in open‐circuit voltage ( V oc ) and fill factor (FF), but these gains degrade by −0.8% abs from the improved state after LS. In contrast, untreated cells exposed to LS show a smaller 0.16% abs gain but maintain better extended stability trends. Precursors exhibit similar degradation patterns to finished cells, confirming the origin lies within the silicon layers. Symmetrical structures show that i/n layers remain stable under LS, whereas i/p layers exhibit noticeable degradation. However, in the dark and under light–dark cycles, i/n layers contribute most to degradation, whereas i/p layers maintain repeatable recovery with successive light exposure. These differences highlight the importance of cyclical testing in understanding field‐relevant stability. Minority carrier lifetime ( τ eff ) modeling and ToF‐SIMS analysis link performance gains to reduced interface defect density ( D it ) and improved surface potential ( φ surf ), both driven by hydrogen redistribution at the interface and dopant interaction. These findings highlight the trade‐off between initial performance and extended stability trends, guiding improved nc‐Si treatment strategies.