Cu2O-n thin films were successfully electrodeposited from a Cu(II) lactate solution containing different concentrations of copper(II) sulfate (CuSO4) and 1 M lactic acid (C3H6O3) at pH 6.5. The electrochemical behaviour of Cu2O thin films has been investigated by means of cyclic voltammetry (CV), chronoamperometry (CA). The nucleation behaviour of the deposited Cu2O has been studied on FTO substrates as a function of Cu2+ concentration. It was found that the nucleation changes from progressive to instantaneous with increasing Cu2+ concentration. Many electrochemical parameters were investigated such as transfer coefficient, diffusion coefficient, cathodic and anodic charges, nucleation rate etc. The effect of the nucleation mechanism on microstructural and optical properties of Cu2O were investigated by X-ray diffractometry (XRD) and ultraviolet visible spectrophotometry (UV–Vis–NIR) and photoluminescence (PL). The optimal concentration of Cu2+ ions was found to be 0.075 and 0.1 M obtained with instantaneous nucleation process. The high photoluminescence (PL) efficiency observed indicating good optical properties with a high carrier density, small depletion layer, high photo-generated electron–hole pairs, narrow band gap and low charge transfer resistance. This results exhibit a high photoelectric performance.