Effect of precursor molar concentration on electrical parameters of Ag/CuO/n-Si/Ag heterojunction under dark and light conditions

In this work, Ag/CuO/n-Si/Ag heterojunction photodiodes were successfully fabricated using a simple and environmentally friendly sol-gel dip-coating technique, and the influence of CuO precursor molar concentration (0.3 M and 0.75 M) on their electrical transport and photodetection characteristics was systematically investigated. Current-voltage (I-V) measurements were performed under dark conditions and illumination intensities ranging from 100 to 200 mW cm −2 . The electrical parameters, including the ideality factor, saturation current, zero-bias barrier height, series resistance, shunt resistance, and rectification ratio, were extracted using the thermionic emission (TE) model and Cheung's method. The results demonstrate that increasing the precursor concentration significantly improves the electrical quality of the heterojunction and promotes more efficient photogenerated carrier transport under optical illumination. The photodiode fabricated with a 0.75 M CuO precursor exhibited enhanced reverse photocurrent, lower series resistance, higher responsivity and photosensitivity, together with effective dark-current suppression, indicating improved carrier separation and collection efficiency within the depletion region. The relatively stable barrier height under different illumination levels further confirms the electrical stability of the heterojunction during photodetection. These improvements are attributed to enhanced optical absorption and optimized charge transport resulting from the improved CuO thin-film characteristics. These results demonstrate that increasing the precursor concentration from 0.3 M to 0.75 M improves the electrical quality of the CuO/n-Si junction and enhances photogenerated carrier extraction, resulting in higher photocurrent, responsivity, and photosensitivity while maintaining low dark-current levels. The main contribution of this work is to establish precursor molar concentration as a simple and effective processing parameter for tuning the coupled electrical transport and photoresponse of solution-processed Ag/CuO/n-Si/Ag heterojunction photodiodes.