The effects of coumarin additive on the properties of CdS thin films grown by chemical bath deposition

CdS thin films have been obtained on glass substrates by using chemical bath deposition technique. Different concentrations of coumarin were used as an additive in the growth solutions, for the first time. The effects of coumarin on the properties of the as-deposited and annealed CdS thin films were investigated. It was found that increasing coumarin concentration in the growth solution remarkably affects the crystallinity and uniformity of the films. The 1% and 2% presence of coumarin enhanced the surface morphology while higher concentrations decreased surface uniformity. In the optical band gap values of both as-deposited and annealed films, a decrease has been observed with increasing additive concentration. Through temperature dependent resistance measurements of the films, impurity levels׳ electrical activation energies for each film have been estimated by means of the obtained discrete linear regions indicating different conduction mechanisms.