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In this study, we report highly stable photoactive quaternary metal chalcogenide Cu2ZnSnS4 nanocrystals synthesis from low cost, ecofriendly, non-toxic and earth-abundant elements for photovoltaic devices. Their electro-optical properties such as, tunable band gap, high-absorption coefficient and wide absorption window make them highly suitable materials to be utilized as absorber layer and counter electrode in various types of solar cells. For this purpose, first we synthesized Cu2ZnSnS4 nanocrystals by colloidal, co-precipitation, wet chemical and hydrothermal methods using stabilizing agents under variable reaction conditions. Afterwards, hydrothermal method was employed to synthesize nanocrystals of Cu2CoSnS4, Cu2FeSnS4, Cu2SrSnS4 and Cu2NiSnS4 by replacing Zn with Co, Fe, Sr and Ni metals. The UV–Vis absorption spectra indicate the nanocrystals can absorb entire visible region of electromagnetic radiation and their band gaps range from 1.5 to 1.7 eV. The X-ray diffraction (XRD) patterns confirm the formation of kieserite phase of all nanocrystals with a crystallite size of approximately 6–10 nm. These nanocrystals are coated on surface of the synthesized ZnO nanoparticles to study their application as absorbing layer in quantum dots-sensitized solar cells (QDSSCs). Moreover, they were adsorbed on ITO substrate to study their utilization as counter electrode of dye-sensitized solar cells (DSSCs). The solar cells exhibit efficiencies of 1.2–1.8%, which prove the synthesized nanocrystals can perform excellent role as light absorber and counter electrode in any kind of solar cell device.