Characterization and photoelectrochemical properties of CICS thin films grown via an electrodeposition route

Abstract

In this work, cerium doped CuInS₂ (CIS) polycrystalline thin films with different Ce content are firstly synthesized on indium doped tin oxide (ITO) glass via a low-cost electrochemical technique. The electrochemical nucleation and growth kinetics of a Cu–In–Ce alloy in a triethanolamine (TEA) plating bath solution onto the ITO glass substrate were investigated by cyclic voltammetry (CV) and chronoamperometry (CA). The composition of CuIn_1−xCe_xS₂ (CICS) films was varied by substituting In with Ce with 0 ≤ x ≤ 0.15 (x = Ce/Ce + In). The structural, morphological, optical, and photoelectrochemical (PEC) properties of CICS films were studied as a function of Ce content. X-ray diffraction (XRD) analysis revealed that the annealed CuIn_1−xCe_xS₂ (x = 0, 0.05, 0.1, 0.15) thin films crystallize in a tetragonal chalcopyrite structure with preferential orientation along the (112) plane. Moreover, the crystalline quality and the preferential orientation of CICS films were enhanced up to 0.1 at% of doping concentration. The Raman spectrum results confirmed the establishment of the predominant phase, which corresponds to a CICS chalcopyrite structure and β-In₂S₃ as secondary phase. The surface morphology and elemental analysis of these samples were respectively investigated by scanning electron microscopy (SEM) and energy dispersive X-ray technique (EDS). AFM analysis confirmed the alteration of the surface microstructures of CICS thin films owing to Ce content and the associated RMS roughness value was ranging from 5.73 nm to 10.34 nm. UV-visible spectroscopy results exhibited that the energy band-gap of CICS films can be tuned by cerium content. A Mott–Schottky plot revealed the formation of p-type electrical conductivity with carrier density and flat-band potential of CICS thin films of about 2.6 × 10¹⁶ cm⁻³ and −0.15 V, respectively. Amongst all photo-cathodes with various Ce dopant concentrations, the sample CuIn_0.9Ce_0.1S₂ exhibited a higher photocurrent density than the other samples, which suggests the lowest recombination of photo-generated electron–hole pairs in the depletion region.