Influence of excitation frequency on structural and electrical properties of spray pyrolyzed CuInS2 thin films

This paper reports the cost effective deposition of the copper indium sulfide (CuInS2) thin films under atmospheric conditions via ultrasonic spray pyrolysis. Structural and electrical properties of these films have been tailored by controlling the nozzle excitation frequency and the solution loading. Smoother films have been obtained via 120 kHz excitation frequency compare to the 48 kHz. Band gap energy of the films has also been tailored via excitation frequency. UV-vis-NIR analysis revealed that films deposited at 48 kHz excitation frequency had lower band gap energies. Although, both excitation frequencies resulted chalcopyrite structure, crystallinity of the CuInS2 films was better for 120 kHz. On the other hand, better optical absorption in visible and near infrared region was observed at 48 kHz. Moreover, room temperature electrical conductivity of the samples deposited at 48 kHz excitation frequency was higher than that of samples deposited at 120 kHz. Temperature dependent electrical conductivity data showed that variable range hopping mechanism can be used to explain the conduction of spray pyrolyzed CuInS2 thin films. Electrical mobility as high as 48 cm2/Vs has been observed for the sample deposited from 0.51 ml/cm2 loading at 48 kHz excitation frequency. This value is very close to the mobility of vacuum deposited thin films like amorphous silicon, which is one of the most commonly used semiconductor in electronic and energy applications.