[6,6]-Phenyl C61-butyric acid methyl ester (PCBM) is a good electron transport material and can be employed in optoelectronic application. To understand the effect of the amount ratio on the capacitive behaviors, the pristine ZnO, 3%, 5% and 10% amounts PCBM (low amount) added ZnO interfacial layered Al/ZnO:PCBM/p-Si heterojunction structures have been fabricated by sol–gel spin-coating method and characterized by X-ray diffraction (XRD), capacitance–voltage (C-V) and conductance-voltage (G-V) measurements for the frequency range between 10 kHz and 1 MHz. Some electrical parameters of the pristine ZnO and various PCBM added ZnO interlayered devices have been calculated from 1/C2-V (1/capacitance2-voltage) plots for various frequencies. Moreover, capacitance transient (C-t) and conductance-transient (G-t) measurements of the Al/ZnO:PCBM/p-Si devices have been performed for various light illumination intensities from 20 to 100 mW/cm2 with 20 mW/cm2 increments under light illumination which has whole spectral matching. The results revealed that PCBM amount has a great effect on capacitance and conductivity values of the Al/ZnO:PCBM/p-Si devices.