Study of electrodeposited ZnS thin films grown with ZnSO4 and (NH4)2S2O3 precursors for use in solar cells

Electrodeposited thin films of zinc sulphide (ZnS) are researched and developed for thin film solar cells. The sulphur source, ammonium thiosulphate [(NH4)2S2O3)] is used for the first time to prepare the aqueous electrolytes with zinc sulphate (ZnSO4) as the source of zinc ions. The deposited thin films of ZnS were characterised usingoptical absorption for bandgap estimation, X-ray diffraction (XRD) for identification of phases and structure, Scanning Electron Microscopy (SEM) for surface morphology, Energy Dispersive X-ray (EDX) for composition and photoelectrochemical (PEC) cell to determine the electrical conduction type. The optical absorption shows the bandgapis in the range(3.70 - 3.90) eV. XRD shows the ZnS layers are amorphous and SEM reveals their grain sizes to be ~30 nm. EDX qualitatively shows the presence of Zn and S in these layers. By using PEC cell, both n-type and p-type electrical conductivity have been detected in ZnS layers under various zinc ion concentrations and growth voltages. Initial CdTe based solar cells using ZnS as the window layer produced PV active devices with efficiency of ~2%. The glass/FTO/ZnS/CdTe/Au structures produced device parameters; Voc ~ 510 mV, Jsc ~ 12 mAcm-2 and FF ~ 0.40 indicating the possibility of further improvements. These results will be presented in this paper, and the work is continuing.