Low open circuit voltage (VOC) has been recognized as the number one problem in the current generation of Cu2ZnSn(Se,S)4 (CZTSSe) solar cells. We report high light intensity and low temperature Suns-VOC measurement in high performance CZTSSe devices. The Suns-VOC curves exhibit bending at high light intensity, which points to several prospective VOC limiting mechanisms that could impact the VOC, even at 1 sun for lower performing samples. These VOC limiting mechanisms include low bulk conductivity (because of low hole density or low mobility), bulk or interface defects including tail states, and a non-ohmic back contact for low carrier density CZTSSe. The non-ohmic back contact problem can be detected by Suns-VOC measurements with different monochromatic illumination. These limiting factors may also contribute to an artificially lower JSC-VOC diode ideality factor.
@article{arxiv.1406.2326,
title = {Suns-V$_\textrm{OC}$ characteristics of high performance kesterite solar cells},
author = {Oki Gunawan and Tayfun Gokmen and David B. Mitzi},
journal= {arXiv preprint arXiv:1406.2326},
year = {2016}
}