Effect of heat treatment on electrical properties of fluorine doped tin dioxide films prepared by ultrasonic spray pyrolysis technique

Fluorine doped tin dioxide (FTO) films were prepared on glass substrates by a homemade ultrasonic spray pyrolysis system and the electrical properties were improved by annealing in air. The as-deposited film was prepared from SnCl4 solution. This spray solution prepared from tin tetrachloride pentahydrate (SnCl4 5H2O) dissolved in deionized water at 0.3 M concentration and NH4F was added into the solution for fluorine doping. The NH4F/SnCl4 ratio was varied as 0, 5, 10, 20 and 40%mol, respectively. All of films were prepared at the same period of time, 15 minutes, and substrate temperatures of 300oC. The lowest resistivity of prepared films was found about 8.40x10-1 Ω cm at the optimum NH4F/SnCl4 ratio of 10%mol. The heat treatment parameters were annealed temperature and time. The annealed temperature was varying as 200, 250, 300 and 350 oC and annealed times were set at three different values as 15, 30 and 45 min. for each annealed temperature. After heat treatment process, the transmittance in the near infrared range was decreased due to the decreasing of resistivity.