Premium
The impact of alkali elements on the degradation of CIGS solar cells
Author(s) -
Theelen Mirjam,
Hans Vincent,
Barreau Nicolas,
Steijvers Henk,
Vroon Zeger,
Zeman Miro
Publication year - 2015
Publication title -
progress in photovoltaics: research and applications
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.286
H-Index - 131
eISSN - 1099-159X
pISSN - 1062-7995
DOI - 10.1002/pip.2610
Subject(s) - alkali metal , copper indium gallium selenide solar cells , sodium , potassium , degradation (telecommunications) , grain boundary , equivalent series resistance , open circuit voltage , materials science , chemistry , solar cell , mineralogy , chemical engineering , voltage , composite material , optoelectronics , metallurgy , microstructure , electrical engineering , organic chemistry , engineering
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.