Journal
ENERGY & ENVIRONMENTAL SCIENCE
Volume 14, Issue 6, Pages 3567-3578Publisher
ROYAL SOC CHEMISTRY
DOI: 10.1039/d1ee00260k
Keywords
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Funding
- Conseil de lAction Internationale (CAI)
- F.R.S.-FNRS
- Walloon Region [1117545]
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The study examines the controversial role of cation disorder in the low open-circuit voltage of CZTS kesterite absorber. It suggests that extensive disorder stabilizes the formation of Sn-Zn antisite, contributing to the V-OC deficit. The methodology presented in this work offers insight into optimizing kesterite solar devices for higher efficiency.
The controversial role of cation disorder in the extraordinarily low open-circuit voltage (V-OC) of the Cu2ZnSnS4 (CZTS) kesterite absorber is examined through a statistical treatment of disorder within the cluster-expansion method. It is demonstrated that the extensive Cu-Zn disorder alone cannot be responsible for the large Urbach tails observed in many CZTS solar cells. While the band gap is reduced as a result of the Gaussian tails formed near the valence-band edge due to Cu clustering, band-gap fluctuations contribute only marginally to the V-OC deficit, thereby excluding Cu-Zn disorder as the primary source of the low efficiency of CZTS devices. On the other hand, the extensive disorder stabilizes the formation of Sn-Zn antisite and its defect complexes, which as nonradiative recombination and minority carrier trapping centers dominate the V-OC loss in CZTS. Our analysis indicates that current CZTS devices might have already approached the maximum conversion efficiency (14%) given the limited growth conditions and the remnant cation disorder even after postannealing. In view of the improved efficiency achieved with CZTS-derived kesterite absorbers, the methodology presented in this work offers an avenue to understanding and optimizing these emerging kesterite solar devices towards higher efficiency.
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