Synthesis and characterization of metal oxide based electron transport materials for solar cells

• Low-cost, scalable synthesis of Al:SnO 2 thin films via chemical bath deposition (CBD). • Systematic optimization of Al doping concentration for tunable optical and structural properties. • Polycrystalline SnO 2 thin films with (110) preferential orientation confirmed by XRD. • Band gap tuning from 3.52 eV to 3.76 eV with Al incorporation, suitable for energy level alignment in perovskite solar cells. • Stable n-type conductivity confirmed by hot probe measurements. • Demonstrates CBD as a sustainable route to fabricate high-quality ETLs for perovskite solar cells. . Sustainable energy development has become essential due to fossil fuel depletion and environmental concerns, positioning perovskite solar cells as efficient and low-cost alternatives. In the present study Al-doped SnO 2 thin films were successfully prepared using a simple and low-cost chemical bath deposition (CBD) technique, followed by post-deposition annealing at 300°C for 1 hour in a box furnace. This facile synthesis approach demonstrates the effectiveness of CBD as a scalable approach for producing high-quality electron transport layer (ETL) materials for photovoltaic applications. The structural, optical, and electrical properties of the prepared thin films were comprehensively investigated using X-ray diffraction (XRD), UV-Vis spectroscopy, and the hot probe method, respectively. XRD analysis confirmed polycrystalline tetragonal rutile structure with prominent orientation along the (110) plane, while the crystallite size varied between 8.16-26.68 nm depending on Al doping. UV-Vis analysis showed that the optical band gap was tuneable from 3.52 eV to 3.76 eV as a function of Al incorporation, indicating improved transparency. Hot probe measurements verified stable n-type conductivity in both pristine and doped film samples. An increase in Urbach energy with higher Al doping indicates enhanced lattice disorder and defect density, consistent with previous reports. The low extinction coefficient (k ≈ 0.2-0.4) reflects high optical transparency and smooth film surfaces. This combined features of low-cost, low-temperature aqueous processing, high optical transparency, tuneable bandgap, and stable n-type conduction demonstrate that Al-doped SnO 2 thin films prepared via CBD are strong and promising candidates for electron transport layers (ETL) in perovskite solar cells. .