Electrical Characteristics of Ce 3+ Doped ZnO and Improved Solar Cell Efficiency in p‐CuO/n‐ZnO Heterojunctions

p‐CuO/n‐ZnO heterojunction devices have attracted significant research interest for light‐to‐energy conversion applications due to their favorably aligned energy band positions. Herein, Ce 3+ ‐doped ZnO nanoparticles synthesized via a wet chemical approach are reported, and their physicochemical, optical, and electrical characteristics are investigated. Ce 3+ doping in ZnO resulted in increased crystallite and particle sizes, attributed to the larger ionic radius of Ce 3+ compared to Zn 2+ ions. Optical studies revealed enhanced absorption in the visible region for Ce 3+ ‐doped ZnO nanoparticles, with bandgap values of 3.34, 3.23, 3.15, and 3.07 eV for 0%, 1%, 3%, and 5% Ce 3+ doping, respectively. Enhanced electrical conductivity (from 12.1–18.9 S·cm −1 ), charge carrier concentration, and mobility were observed for 5% Ce 3+ ‐doped ZnO compared to pristine ZnO nanoparticles. Furthermore, p‐CuO/n‐CeZnO based heterojunction solar cell studies revealed that pristine ZnO, 1%, 3%, and 5% Ce 3+ ‐doped ZnO exhibited power conversion efficiencies of 2.29%, 2.55%, 2.61%, and 2.77%, respectively, demonstrating that systematic Ce 3+ doping enhances visible‐light absorption, electrical characteristics, and heterojunction solar cell performance, which has not been comprehensively reported previously.