Copper ions are incorporated into the PbS quantum dots as dopants via a chemical method and an ion irradiation method. For irradiating the samples, a 100 MeV copper swift heavy ion beam is used with three different doses of 1 × 10¹¹, 3 × 10¹¹, and 1 × 10¹² ions/cm². The doped and irradiated samples are characterised by different techniques and introduced as a sensitising layer in a solar cell. The current density–voltage characteristics of the solar cells are studied under white light illumination conditions and the solar cell parameters such as J _sc, V _oc, fill factor, and efficiency are obtained. Efficiency as high as 4.78% is obtained for irradiated quantum dots, which is significantly higher than that of pristine and doped quantum dot solar cells. However, at higher ion dosage, the solar cell efficiency degrades due to unwanted particle agglomeration in quantum dots.