The optical transmittance was determined by taking the average value in the visible light region ranging between 400 nm and 700 nm in wavelength. Figure 2 illustrates the optical transmittance of the IZTO films deposited on glass substrate. Among all films, as-deposited IZTO film showed the lowest average transmittance of about 84%. The band gap energy value of IZTO films was estimated from the inset in Figure 2, which was done by extrapolating the linear part of hν versus (αhν)2 graph to the x axis according to Tauc equation . The average optical band gap energy value was estimated at 3.25 eV, while there was no significant difference, even after annealing treatment. An optical band gap value of about 3 eV was reported from IZTO with composition of 50 at % zinc and 30 at % indium , as increasing indium and zinc deteriorated the optical transmittance and decreased the optical band gap energy of IZTO thin films . Nevertheless, a shift in band gap energy and average transmittance values was reported elsewhere by composition variation of IZTO . This is why an annealing treatment did not alter the band gap value of the IZTO film. Overall, the optical properties of all IZTO films exhibited high average transmittance above 80% and relatively high band gap energy, which is desirable for transparent display application.