Annealing strategies for spin-coated ZnO thin film for an electron transport layer application for perovskite solar cell

This study explores how various post-deposition annealing techniques influence the structural, optical, and electrical characteristics of spin-coated ZnO thin films on glass substrates for electron transfer layer (ETL) for perovskite solar cell fabrication. Comprehensive analysis was carried out using XRD, XPS, FESEM, UV–Vis transmittance analysis, photoluminescence, Raman spectroscopy, and four-probe measurements conducted at room temperature to evaluate the structural, optical, and electrical properties of the films. Post-deposition annealing is essential for modifying ZnO thin films, influencing their structure, optical behavior, and electronic properties, making it crucial for material optimization. The XRD results show that the post-deposition annealed ZnO films exhibit a hexagonal phase at 450 °C. The FE-SEM analysis shows significant variation in the formation of ZnO surface structure after post-deposition annealing in different atmospheres. Interestingly, transmittance of the vacuum annealed ZnO thin films significantly improved from the UV to the visible region. The estimated band gap of the annealed ZnO thin films ranges from 3.44 eV to 3.55 eV. Electrical sheet resistance measurements identify an optimum value of 5.93 MΩ/square for the vacuum-annealed film, suggesting enhanced conductivity. Furthermore, the charge transport properties are found to be most favorable in sample annealed under vacuum condition exhibited superior performance compared to others. Our research work not only indicates the different post-deposition annealing process strategies of spin-coated ZnO films but also enlightens the suitable deposition process for the development of a ZnO based ETL for PSC device. The results obtained from the photovoltaic device indicate that the vacuum annealed ZnO thin films can be a potential ETL materials for PSC device.