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

Abstract

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 120kHz excitation frequency compare to the 48kHz. Band gap energy of the films has also been tailored via excitation frequency. UV–vis–NIR analysis revealed that films deposited at 48kHz excitation frequency had lower band gap energies. Although, both excitation frequencies resulted chalcopyrite structure, crystallinity of the CuInS2 films was better for 120kHz. On the other hand, better optical absorption in visible and near infrared region was observed at 48kHz. Moreover, room temperature electrical conductivity of the samples deposited at 48kHz excitation frequency was higher than that of samples deposited at 120kHz. 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 48cm2/Vs has been observed for the sample deposited from 0.51ml/cm2 loading at 48kHz 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.