Cadmium Telluride (CdTe) solar cells are leading the way in efficient, cost-effective, and environmentally friendly solar energy conversion, with a favourable bandgap of 1.45 eV. However, the potential of zinc oxide (ZnO) as a buffer layer, its interaction with copper back contact, and the effect of its thickness on device performance have not been thoroughly investigated. To address this knowledge gap, we fabricated CdTe solar cells using vacuum-assisted chemical vapour deposition, incorporating ZnO as a coating layer. We varied the thickness of the ZnO layer at 0, 10, 20, and 30 nm, while all samples received a 50 nm copper back contact layer. Extensive characterization of CdTe solar cells revealed significant improvements with the addition of a ZnO coating and a copper back contact. Notably, the CdTe solar cell with a copper back contact and a 30 nm ZnO layer exhibited the best optical and electrical performance. X-ray diffraction analysis confirmed the presence of ZnO within the CdTe layer. The CdTe/30 nm ZnO/50 nm Cu configuration demonstrated an increased photocurrent density of 30 mA/cm2, improved electrical conductivity of 3 × 10–3 S/cm, good transmittance of 80%, optimal quantum efficiency of 85%, and a bandgap of 1.6 eV. These findings establish a connection between ZnO layer thickness and solar cell efficiency, providing valuable insights for optimizing CdTe-based photovoltaic devices. © 2025 Elsevier B.V., All rights reserved.