SYNTHESIS OF Al-Ga CO-DOPED TIN OXIDE NANOPARTICLES USING Psidium guajava LEAVES EXTRACT AND CHARACTERIZATION FOR POTENTIAL APPLICATION IN SOLAR CELL

Abstract

A significant percentage of greenhouse gases (GHGs) are emitted during burning of fossil fuel, contributing to climate change by trapping heat leading to an increase in global temperature. Alternative energy sources have been explored as they are considered clean and non-polluting. While solar cells typically have low efficiency in converting sunlight into electricity, doping of metal oxide semiconductors used in solar cells can help resolve this issue. Due to their interesting energy band gaps, which can be readily adjusted by doping with foreign elements, metal oxide semiconductors like tin oxide have a wide range of applications. The research focuses on the synthesis and characterization of undoped tin oxide nanoparticles (NPs) with and without Psidium guajava extract, to determine the effects of Al and Ga doping concentrations (0.5, 1.0, 1.5, 2.0 and 2.5%) and to investigate the effects of varying Al and Ga co￾doping ratios (25:75, 50:50 and 75:25 %) on the structural, luminescence and optical properties of tin oxide nanoparticles. Synthesis was done using green synthesis method by utilizing Psidium guajava as caping agent and the nanoparticles were characterized using Photoluminescence spectrophotometer (PL), ultra-violent visible spectrophotometer (UV-Vis), X-ray diffractometer (XRD) and Fourier transform infrared spectrophotometer (FTIR). From the UVVis results, the band gap of capped and uncapped tin oxide was 3.98 and 3.21 eV, respectively. The band gap decreased upon doping and co-doping. For capped Al, Ga and Al: Ga-SnO2, obtained band gap were within 2.01-2.88, 2.29-3.25 and 1.58-1.69 eV, respectively. For uncapped Al, Ga and Al: Ga-SnO2, optical band gaps were within 2.38-2.89, 2.46-3.07 and 3.063.14 eV, respectively. Using the Scherrer equation, crystallite sizes of 14.89 and 18.00 nm were calculated for capped and uncapped SnO2. For Al-doped SnO₂, the smallest crystallite sizes were observed at 2.0% doping (capped, 10.57 nm) and 1.5% doping (uncapped, 12.47 nm). For Ga-doped SnO₂, the smallest sizes were at 2.5% (capped) and 1.5% (uncapped). PL spectra showed a strong emission peak and a broadband in the 460-480 nm range, attributed to the defect and oxygen vacancy recombination. For capped Al-SnO2, Ga-SnO2 and Al:Ga-SnO2, the highest PL intensities were observed at 2% Al, 0.5% Ga and 75:25 Al:Ga-SnO2 ration, peak intensities were highest at 2.0 % Al, 2.0% Ga, and a 75:25 ratio. The lowest PL intensity peaks were observed at 2.5 % Al, 1.0 % Ga and 25:75 Al:Ga-SnO2 ratio in both capped and uncapped samples. Doping and co-doping significantly tuned SnO₂ nanoparticle properties, improving their optical and structural characteristics for potential solar applications. Future studies should explore other green synthesis routes and dopant elements to further enhance SnO₂ efficiency in optoelectronic devices.