Structural, vibrational, optical, morphological and compositional properties of CdS films prepared by a low-cost electrochemical technique

Very dense and uniform thin films of CdS were deposited on fluorine-doped tin oxide (FTO) substrates for thin film semiconductor devices application, such as in solar cells. The simplified electrochemical deposition method applied uses two-electrode system with FTO as the working electrode and high-purity graphite rod as the counter electrode. The CdS films grown at different cathodic voltages (1500 mV, 1550 mV and 1600 mV) were characterized for their structural, vibrational, optical, morphological and chemical compositional properties using state-of-the-art glancing incidence X-ray diffraction (GIXRD), Raman spectroscopy, UV–Visible spectrophotometry, scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) respectively. XRD results reveal the existence of pure hexagonal crystal structure of CdS in the films in both as-grown and heat-treated conditions. The size of crystallites are in the range of (9–14) nm and (11–17) nm while the size of grains in these highly uniform and dense films are in the range (180–860) nm and (270–880) nm before and after annealing respectively. Raman results show the typical fingerprint of CdS in the form of the 1LO and 2LO phonon vibration peaks. The energy bandgaps obtained from optical measurements fall in the range of (2.50–2.59) eV which narrow down to 2.42 eV after annealing, for the different growth voltages used. EDX reveals all the films to be S-rich, with Cd/S ratio of ∼0.9 after annealing.