Journal
SOLAR ENERGY MATERIALS AND SOLAR CELLS
Volume 159, Issue -, Pages 447-455Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.solmat.2016.09.034
Keywords
CZTSe solar cell; Defects states; Carrier density; Admittance spectroscopy; Ratio of Zn/Sn
Funding
- National Natural Science Foundation of China [61274053, 51372121, 51472239, 51572132]
- YangFan Innovative & Entrepreneurial Research Team Project [2014YT02N037]
- New & Renewable Energy of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) grant - Korea government Ministry of Trade, Industry and Energy [20123010010130]
- National Research Foundation of Korea (NRF) - Korean government [NRF-2014R1A2A1A11053109]
- National Research Foundation of Korea [22A20151113064] Funding Source: Korea Institute of Science & Technology Information (KISTI), National Science & Technology Information Service (NTIS)
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The defects states and carrier density of CZTSe absorber layers are two of the crucial factors that decide the photovoltaic performance of CZTSe thin film solar cells. Fine tailoring the defects and carrier density is a key to push the power conversion efficiency of CZTSe solar cells to a more competitive level. In this work, the phase properties, defect states, and carrier density of CZTSe thin film are well controlled by fine tuning the ratio of Zn/Sn in the range from 0.75 to 1.27. Capacity-Voltage measurements and Admittance Spectroscopy are used to characterize the carrier density, depletion region width, and defect states of the CZTSe solar cells. The results indicate that the defects states and carrier density of CZTSe layer are very sensitive to the ratio of Zn/Sn. Combining experimental results and numerical simulation, the statistic regularities of the photovoltaic parameters of the CZTSe solar cells with different ratios of Zn/Sn is well explained. The increase of V-OC of CZTSe solar cells with the ratio of Zn/Sn is related to both the increased carrier density and the decreased deep level defects states. The decline of J(SC) of the Zn-rich solar cells is caused by both the shrunken depletion region width and a large barrier caused by ZnSe phase. This barrier is the cause for a low fill factor in the Zn-rich solar cells. Overall, the CZTSe solar cells with a stoichiometric ratio of Zn/Sn=1.02 have favorable defects property and carrier density, thus resulting in the highest photovoltaic efficiency of 10.21%.
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