Cu2ZnSn(S, Se)(4) (CZTSSe) absorber layers are fabricated by co-electrodeposited Cu-Zn-Sn-S (CZTS) precursors followed by selenization. In order to complex the Cu ions and shift its reduction potential to more negative, trisodium citrate is applied as the complexing agent during the co-electrodeposition. After the coelectrodeposition, CZTS precursors are preliminary annealed at 280 degrees C in order to improve the homogeneity by intermixing of the elements. The influences of selenization temperatures on the chemical compositions, crystal phases, optical properties and photovoltaic device performances are also systematically investigated by X-ray energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), Raman spectroscopy, UV-vis absorption spectroscopy, and J-V measurements. EDS results reveal that the CZTSSe absorber layers are all in a Cupoor and Zn-rich nature, which is beneficial for fabricating cells with high efficiency. It is found that the crystalline quality and morphology of the CZTSSe absorber can be greatly improved by post-selenization at 550 degrees C. Photovoltaic devices are fabricated with standard soda-lime glass (SLG)/Mo/CZTSSe/CdS/i-ZnO/ITO/Ag grid structures. Champion cell demonstrates 2.81% efficiency based on the optimized CZTSSe absorber. These results validate co-electrodeposition as a promising strategy for developing earth-abundant thin film solar cells at low-cost.