Synthesis and Characterization of Zn-doped and un-doped SnO2 nanostructures for PV Applications

Tin oxide nanostructures, un-doped and Zn-doped, have been prepared by conventional sol-gel technique. Research grade tin chloride (SnCl2.2H2O) and zinc acetate (Zn(O2C2H3)2) were used as tin and zinc sources. Ethylene glycol and alcohol were used as solvents under different synthesis conditions. Transparent un-doped and Zn-doped SnO2 sol was prepared after continuous stirring and refluxing at 40C. Thin films, prepared from SnO2 sol, have also been deposited on glass substrate by spin coating at 500 rpm for 10 seconds and then at 3000rpm for 30 seconds. Scanning electron microscopy results show the formation of nanodiamonds (~40nm) and nanorods (~30nm) after annealing at 300C for 60 minutes. It is important to mention here that we have prepared SnO2 nanostructures without the use of any surfactant and ligand during sol synthesis. X-ray diffraction (XRD) patterns show that the preferred orientation was (111) with orthorhombic crystal structure. Crystallite size was calculated to be ~8 nm from XRD results. Optical properties measured by using spectroscopic ellipsometer have shown a band gap of 3.87 eV, which is larger than the band gap of SnO2 in bulk form (3.6eV). More than 90% transmission was observed in these sol-gel deposited SnO2 thin films. Electrical properties were studied using four-probe method and Hall effect. Thin films show room temperature conductivity of the order of 10 Ωcm. These optical and electrical values are comparable to values reported in literature. Zn-doped SnO2 films show conductivity slightly better than the undoped one.