Suns-VOC characteristics of high performance kesterite solar cells

Low open circuit voltage (V-OC) 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-V-OC measurement in high performance CZTSSe devices. The Suns-V-OC curves exhibit bending at high light intensity, which points to several prospective V-OC limiting mechanisms that could impact the V-OC, even at 1 sun for lower performing samples. These V-OC 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-V-OC measurements with different monochromatic illuminations. These limiting factors may also contribute to an artificially lower J(SC)-V-OC diode ideality factor. (c) 2014 AIP Publishing LLC.