The size of PbSe cubes was tuned from microsize to nanosize by glycine as a surfactant using a co-precipitation method. Four samples were synthesized that one was without surfactant and the others were synthesized by different surfactant concentrations. It was observed that the morphology of the sample with the free-surfactant condition was cubic morphology with a microsize feature with an average size of 2 μm. Additionally, adding the surfactant to the synthesis solution led to obtaining PbSe nanocubes with an average size of 35 nm. Electrochemical impedance spectroscopy (EIS) and I-V results of the PbSe nanocubes indicated lower resistance for the smallest sizes of PbSe nanocubes. Furthermore, PbSe nanocubes with the smallest sizes showed a higher absorption coefficient than the other samples did. The capability of the obtained micro and nano PbSe cubes as an absorbing layer in a solar-cell device was examined. The solar-cell measurement results revealed a higher figure of merit for the sample with the lowest size such as 6.9% of power conversion efficiency (PCE) and 75% of fill-factor (FF).