In the presented work Cu2ZnSnSe4 nanocrystals have been synthesized by the polyol method. The chemical composition, morphological, structural, and microstructural properties of Cu2ZnSnSe4 nanocrystals depending on synthesis temperature and time as well as precursor composition have been thoroughly investigated using scanning and transmission electron microscopies, energy dispersive X-ray analysis, X-Ray diffraction, FTIR spectroscopy. We compared the properties of nanocrystals synthesized from different precursors containing selenourea or amorphous selenium as a source of selenium and then determined the optimal conditions for nanocrystals synthesis. It was found that the optimal synthesis time for nanocrystals obtained using the first approach was t = (30-45) min, and for the second approach t = 120 min. It was also found that the optimal composition for the synthesis of single-phase Cu2ZnSnSe4 nanocrystals by the second approach is the molar ratio of precursors 2:1.5:1:4 and synthesis temperature T = 280 оС. Cu2ZnSnSe4 nanocrystals synthesized under optimal conditions were used to develop nanoinks for printing solar cell absorbers by 2D and 3D printers.