Utilizing green-synthesized ZnO nanoparticles as an electron transport layer (ETL) is a key strategy in perovskite solar cell applications, leveraging their high electron mobility, conductivity, stability against photo-corrosion, and cost-effectiveness. In this study, these environmentally synthesized nanoparticles, combined with SnO2, formed a composite solution-processed ETL achieving an impressive 18.09 % device efficiency, with 1.06 V open circuit voltage, 71.71 % fill factor, and 23.80 mA/cm2 short circuit current density. These values underscore the composite material's potential for device applications. Additionally, capacitance measurements investigated ETL and absorber layer interfaces, yielding crucial insights into their behaviour under varying voltage, frequency, and illumination conditions. The study highlights the ZnO-NP and SnO2 composite's efficacy as a superior ETL in PSCs, emphasizing the environmental sustainability implications of employing green-synthesized materials in solar energy technologies.