Herein, Cu doped CdS nanocrystals (NCs) are employed as electron acceptors in hybrid solar cells (HSCs) for the first time. Firstly, undoped and Cu doped CdS NCs with different concentrations (0.15, 0.3, & 0.6 mol %) are synthesized by the heating-up approach. Structural studies exhibited a peak shift towards a higher wavelength due to the replacement of Cd²⁺ ions by Cu²⁺ ions. The shape and size of the particles are explicitly changed with respect to Cu concentration. Furthermore, HSCs are fabricated with the device structure of FTO/ZnO/P3HT:PC₆₁BM:Cu doped CdS NCs/MoO₃/Ag. The highest power conversion efficiency of 3.1% is achieved at 0.3 mol% of Cu doped CdS NCs. It is apparent that Cu dopant played a decisive role in the properties of CdS NCs as well as HSCs performance. Therefore, this work unveils the importance of doping and a new strategy to enhance the performance of the HSCs.