Kesterite or Cu2ZnSn(Se,S)4 (CZTSSe) is an emerging earth-abundant thin-film solar cell technology with current world record of 12.6% which is still far behind its cousin, the CuInGaSe technology. We investigated Suns-Voc characteristics of our high performance kesterite solar cells using two setups: (1) Low intensity (1 sun) Suns-Voc system integrated to the standard solar simulator using motorized continuous density filter. (2) High intensity (∼300 suns) Suns-Voc. The CZTSSe high intensity Suns-Voc curves exhibit bending at high intensity, which reveal several Voc limiting mechanisms that could impact the Voc at 1 sun such as: 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 latter problem can be detected by high intensity Suns-Voc with different infra red bandpass filters. Some of these limiting factors contribute to an artificially lower Jsc-Voc diode ideality factor compared to that of standard light J-V. The Suns-Voc techniques developed here is also applicable to other thin film solar cell technologies.