Band gap engineering and enhancement of electrical conductivity in hydrothermally synthesized CeO2 ̶ PbS nanocomposites for solar cell applications

Abstract

The wide band gap of CeO2 limits its application in solar energy harvesting, notwithstanding the exceptional optical and electrical properties due to the presence of unfilled 4f orbitals. Therefore, we combine a narrow band gap semiconductor PbS with CeO2 for band gap narrowing and to achieve enhanced electrical conductivity in the nanocomposites. CeO2 ̶ PbS nanocomposites were synthesized from a combination of as-prepared CeO2 powder and precursors of lead and sulphur using a two-step hydrothermal reaction process. The morphologies and structures of various nanocomposites synthesized at different concentrations of Pb precursor were studied by Field Emission Scanning Electron Microscopy and X-ray diffraction. The average crystallite sizes of the nanoparticles were estimated from XRD analysis and found to be in the range of 11 ̶ 15 nm for all the CeO2 ̶ PbS nanocomposites. The homogeneity and chemical composition were investigated by Energy Dispersed X-ray Analysis and X-ray photoelectron spectroscopy. Similarly, the microstructure study and lattice imaging were carried out with the help of high-resolution transmission electron microscopy. The lattice structure was corroborated by lattice vibration properties studied by micro-Raman spectroscopy. The surface structure and composition, such as the identification of surface functional group and adsorbed species were ascertained with the help of Fourier Transform Infrared Spectroscopy. The optical properties of the CeO2 ̶ PbS were studied by UV–Vis Diffuse Reflectance Spectroscopy. The optical band gaps of the nanocomposites were estimated to be 2.76 ̶ 2.98 eV. The electrical property of the CeO2 ̶ PbS powder was analyzed by recording the current-voltage characteristics of a series of hydraulic pressed pellets. The electrical conductivity obtained for CeO2 ̶ PbS nanocomposites was found to be much higher than that of pristine CeO2 nanoparticles. Hence, the enhanced electrical property with reduced band gap of CeO2 ̶ PbS nanocomposites makes it suitable for optoelectronic devices and solar cell applications.