Modification of the optoelectronic properties of reactively evaporated In6Se7 thin films by Sn doping for photovoltaic applications

Sn doped In6Se7 thin films with 5wt% and 10wt% Sn are prepared on glass substrate using reactive evaporation technique. The samples are characterized by XRD, FESEM, XPS and UV-Vis-NIR Spectrophotometer. XRD result shows that the samples are polycrystalline with monoclinic structure. Presence of compressive strain and lattice space shrinkage is observed in 10wt% Sn doped sample. A detailed study of the optical properties demonstrated that a blue shift of 0.02eV in the optical band gap of 5wt% Sn doped sample is due to Burstein-Moss effect. Band gap narrowing in 10wt% Sn doped sample is explained in terms of defect induced static disorder. 5wt% Sn doped sample exhibits lowest resistivity and improved photoconductivity compared to undoped sample. This enhancement in optoelectronic properties facilitates the use of such films in photovoltaic applications.