The Kinetics of SHJ Degradation: Time and Stressor Dependent Chemical Analysis and Simulation

Despite record efficiencies, the wide adoption of silicon heterojunction is hampered by higher costs and uncertainties in long-term performance. Although recent publications report performance loss rates comparable to other field-deployed cSi technologies, the limited availability of field data and the dispersion in performance degradation results - particularly in open-circuit voltage - remain significant concerns. Various factors, including bulk and interfacial defects, charge carrier recombination dynamics, and environmental stressors such as temperature and humidity, contribute to this degradation. Understanding the mechanisms behind the open circuit voltage degradation as well as the kinetics involved is essential for developing mitigation strategies that enhance the reliability of SHJ devices.In this paper we present a fundamental understanding of the mechanisms governing open circuit voltage degradation by coupling density functional theory, molecular dynamics and experimental measurements tracking electrical and chemical changes at the interfaces under different stressor conditions. We employ Glow Discharge Optical Emission Spectroscopy (GDOES) and X-ray Photoelectron Spectroscopy (XPS), to assess hydrogen and oxygen motion and associated changes in the bonding environment. Lifetime spectroscopy and external radiative efficiency help connect these chemical changes to variations in recombination and selectivity. Results indicate that after 10 years in the field, modules lose hydrogen and gain oxygen in consort with environmental stressors, and that these chemical changes are consistent with the deterioration of electrical properties. Results from molecular dynamics suggest that ambient humidity influences the movement of hydrogen and oxygen within the SHJ structure ultimately dictating the kinetics.