<p>Colloidal semiconductor nanocrystal solar cells have been extensively developed in recent years and achieved a power conversion efficiency of ~ 15%. However, cost, toxic constituent elements, and pure-phase materials synthesis are major concerns for large-scale commercialization. Here in this report, we have successfully synthesized pure-phase crystalline Cu₂MnSnS₄ nanocrystals using the hot injection method which is further carefully characterized by various state-of-the-art techniques to investigate its structural, morphological, and optoelectronic properties. The high optical absorption and optimal band gap of 1.1&#xa0;eV are observed, which is highly suited for solar cell applications. Furthermore, we pioneered the idea of fabricating the Cu₂MnSnS₄ nanocrystal-sensitized solar cell. We achieved a notable power conversion efficiency of 1.1% (~ fourfold higher) with n-CdS buffer layer than w/o n-CdS, 0.3%. The enhanced efficiency is directly attributed to the improved charge transfer and retard charge recombination across the p-Cu₂MnSnS₄/n-CdS interface. So far, to the best of our knowledge, we report the highest power conversion efficiency of 1.1% for Cu₂MnSnS₄ nanocrystals sensitized solar cell and energy&#xa0;band diagram for understanding the mechanism. The results were validated using an energy band diagram constructed using the cyclic voltammetry technique.</p>