Effect of different thermo-treatment at relatively low temperatures on the properties of indium‑tin-oxide thin films

Pulsed DC magnetron sputtering was used to deposit indium‑tin-oxide (ITO) thin films on glass substrates for application in photovoltaic devices as the final window layer. The evolution of crystal phase, morphology, resistivity and transmittance of the ITO films under different thermal annealing procedure (in-situ annealing versus post-annealing) at relatively low temperatures (up to 300 °C) were studied. Fully crystalline ITO films with low sheet resistance of 24 Ω/□ and high average transmittance (exclude glass substrate) of 90.10% with a Haacke's figure of merit 1.47 × 10^− 2 Ω⁻¹ were obtained by in-situ annealing at 200 °C. In comparison, the minimum temperature observed to fully crystalize the ITO thin films with competitive crystallinity, electrical and optical properties by post-annealing was 250 °C. The corresponding post-annealed 300 nm thick films showed sheet resistance of 49 Ω/□ and average transmittance (exclude glass substrate) as high as 91.93% with a Haacke's figure of merit 0.882 × 10^− 2 Ω⁻¹. The surface morphology of the as-deposited ITO films remained homogeneous after post-annealing whereas large particles (up to 100 nm) were observed on the surface of the films deposited by in-situ annealing. The results indicated that different thermal treatment procedures at lower temperatures produce significant effect on the electrical, optical and other physical properties of the ITO thin films which are critical for the window layer in photovoltaics.