Unencapsulated CIGS solar cells with high and low contents of sodium (Na) and potassium (K) were simultaneously exposed to damp heat and illumination. The solar cells with a high alkali (Na, K) content exhibited higher initial conversion efficiencies, but degraded severely within 100 h, while the alkali poor samples kept relatively stable performance under damp heat and illumination. The degradation of the samples with a high alkali content resulted in the formation of sodium rich spots on the top ZnO:Al surface of the samples. This is likely caused by light‐induced Na + migration via the grain boundaries in the absorber to the depletion region, where the Na + accumulated. This allowed subsequent Na + transport through the depletion region due to the lowering of the internal electric field caused both by the Na + accumulation and illumination. The migration resulted in the formation of shunt paths, which reduced the shunt resistance and open circuit voltage. Furthermore, ingression of water into the ZnO:Al is expected to be responsible for a slow but steady increase in series resistance for both high and low alkali solar cells. Additionally, sodium migration led to a severe increase of the series resistance in case of alkali rich samples. Copyright © 2015 John Wiley & Sons, Ltd. Module like alkali rich CIGS solar cells degrade quickly under combined exposure to damp heat and illumination, while alkali poor solar cells are relatively stable. The degradation is likely caused by the migration of sodium ions from the CIGS layer to the depletion region and further, which occurs due to the internal electric field.


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    Title :

    The impact of alkali elements on the degradation of CIGS solar cells



    Published in:

    Publication date :

    2015




    Type of media :

    Article (Journal)


    Type of material :

    Print


    Language :

    English



    Classification :

    BKL:    53.36 Energiedirektumwandler, elektrische Energiespeicher