A study on the improved growth rate and morphology of chemically deposited ZnS thin film buffer layer for thin film solar cells in acidic medium

Zinc sulfide (ZnS) thin films have been prepared by chemical bath deposition method with improving growth rate and morphology using the mixed complexing agents of ethylenediamine tetra-acetate disodium salt (Na₂EDTA) and hexamethylenetetramine (HMTA). The effects of HMTA quantity on the morphological, compositional, optical, structural and electrical properties of ZnS thin films with fixed Na₂EDTA concentration have been investigated. ZnS thin films were deposited on glass substrates using aqueous solutions containing zinc acetate dehydrate and thioacetamide in acidic medium (pH 4). Field emission scanning electron microscopy results show that the morphology of a deposited ZnS thin film using HMTA as a complexing agent is rough. However, very uniform and smooth ZnS thin films are obtained using mixed complexing agents of Na₂EDTA and HMTA. The growth rate and root mean square of ZnS thin films are improved with increasing HMTA quantities. X-ray diffraction patterns show that all the ZnS thin films are grown as a hexagonal structure without secondary phase (ZnO) regardless of HMTA quantity. Optical band gap energy of ZnS thin films deposited using mixed complexing agents increase from 3.75 to 3.87eV with increasing quantity of HMTA.