Degradation-Related Defect Level in Weathered Silicon Heterojunction Modules Characterized by Deep Level Transient Spectroscopy

Journal Article · Thu Sep 07 04:00:00 EDT 2023 · Solar Energy Materials and Solar Cells

DOI:https://doi.org/10.1016/j.solmat.2023.112527· OSTI ID:2004923

Johnston, Steven W.; Jordan, Dirk C.; Kern, Dana B.; Colvin, Dylan J.; Davis, Kristopher O.; Moutinho, Helio R.; Kroeger, George F.

Commercial silicon heterojunction photovoltaic modules, known as amorphous-silicon-based heterojunction with intrinsic thin-film layer (HIT) modules, show average degradation after 10 years in the field. HIT modules weathered outdoors in Colorado and Florida display mostly uniform decreases in intensity when mapped with photoluminescence (PL) imaging compared to a control module. Flash-table-based current-voltage curves show that degradation is dominated by voltage loss. Samples are cored from each of the modules, and deep level transient spectroscopy (DLTS) detects three electron-trap defect states in all modules with activation energies of electron emission from the defects of 0.07, 0.16, and 0.50 eV. DLTS measurements on the weathered modules show an additional deep-level, electron-trap defect state with an activation energy of 0.51 eV and a trap density of approximately 10^12 cm^-3. The capture rate is measured using varying short filling pulse times, and the resulting capture cross section is estimated to be 1.1x10^-16 cm^2. The development of the weathering-related defect level correlates to decreases in carrier lifetime, PL intensity, and module voltage. Various depths of the space charge region are probed with increments in applied reverse bias and filling-pulse bias. This DLTS depth profiling shows a trend of trap density increasing with less applied reverse bias, suggesting that the weathering-related defect increases carrier recombination toward the interface between the bulk silicon wafer and the junction-forming amorphous-silicon passivation layers.

• Research Organization: National Renewable Energy Laboratory (NREL), Golden, CO (United States)
• Sponsoring Organization: USDOE Office of Energy Efficiency and Renewable Energy (EERE), Renewable Power Office. Solar Energy Technologies Office
• DOE Contract Number: AC36-08GO28308
• OSTI ID: 2004923
• Report Number(s): NREL/JA-5K00-86484; MainId:87257; UUID:a14f215a-e81a-4c56-bebd-9741e6b0aeb0; MainAdminID:70679
• Journal Information: Solar Energy Materials and Solar Cells, Journal Name: Solar Energy Materials and Solar Cells Vol. 262
• Country of Publication: United States
• Language: English

Related Subjects

SOLAR ENERGY
charge carrier lifetime
degradation
laser ablation
photovoltaic cells
semiconductor impurities
solar panels