Simulation and experimentally investigation on cupric oxide (CuO) and zinc oxide (ZnO) based heterojunction solar cells (HJSC) fabricated using the sol–gel spin coating technique has been presented in this contribution. It is seen from simulated results, the photoconversion efficiency (PCE) of the hetero-junction solar cells employing with structure FTO/ZnO/CuO/Al can be enhanced through engineering on the thickness of photoactive layers, band gap and carrier concentration of photoactive materials. AMPS-1D simulated result showed cells efficiency of ∼5.5%, current density (Jsc) of 6 mA/cm2, open circuit voltage (Voc) of 0.9 V and fill-factor (FF) of 80%. Whereas solar cell fabricated with spin coating technique using optimized parameters from simulated results with conventional structure demonstrated a power conversion efficiency exceeding 1.15% with Vocof 1.36 V, Jsc of 1.99 mA/cm2 and FF of 53% without electron transport layer (ETL), hole transport layer (HTL) and anti-reflecting coating (ARC). Deposited film properties like structural, surface morphological, photovoltaic and optical were studied by using X-ray diffraction (XRD), scanning electron microscopy (SEM), and light current density–voltage (J–V) with AM1.5 solar simulator and UV-vis Spectroscopy. Although there is a variation between simulation and experimental results due to open air fabrication environment with no charge transport layers and no anti-reflection coating, this value of inorganic HJSC efficiency is possibly the highest reported for a ZnO/CuO interface fabricated using spin coating technique that highlights spin coating as a promising technique for inexpensive and scalable fabrication of ZnO/CuO based hetero-junctions solar cell.