The role of potassium in grain boundaries of flexible CZTSSe thin film solar cells
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The electrical property at the grain boundaries (GBs) of Cu2ZnSn(S,Se)4 (CZTSSe) thin film is very important to fabricate a high efficiency device and it is closely interrelated with alkali elements. Here, we used Kelvin probe force microscopy to confirm that spike-type contact potential difference formed at the GBs in CZTSSe thin film after potassium (K) doping, which could attract the electrons to travel through the grains boundaries and was favorable for obtaining a device with better performance. K also could promote the grain growth of CZTSSe thin films. With the help of K doping, a flexible CZTSSe solar cell with an efficiency over 3% was obtained.
This work was financially supported by National Natural Science Foundation of China (Grant Nos. 11504177, 61774084), Natural Science Foundation of Jiangsu Province (Grant Nos. BK20160909, BK20171442) and NUPTSF (Grant No. NY218109).