Effects of deposition temperature and CdCl2 annealing on the CdS thin films prepared by pulsed laser deposition

Abstract

Pulsed laser deposition (PLD) technique is suitable for the deposition of high-quality compound semiconductor thin films, and has been widely developed in recent years. However, pulsed laser deposition of CdS films has rarely been reported. In this work, we prepared CdS thin films using PLD. The effects of growth temperature on the PLD-CdS thin films were studied towards high-performance CdS/CdTe thin film solar cells. Results showed that the CdS film prepared at 400 °C has the best crystallinity and optical transmittance, while 200 °C is more suitable for the window layer of CdTe solar cells due to the highest energy conversion efficiency and the best short-wavelength response. CdCl2 annealing treatment was also employed on the 200 °C-deposited and 400 °C-deposited PLD-CdS layer. Annealing treatment further enhanced crystallinity, and obviously enlarged the grain size. Optical transmittance spectra showed that the band gap of the CdS films increased after annealing. Fermi level of CdS films shifted closer to the conduction band from XPS analysis. CdTe solar cells with annealed windows obtained further improved performance, including higher short-circuit current, open-circuit voltage and energy conversion efficiency.