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Thin films based on barium fluoride (BaFx) have demonstrated the capability to reduce the work function of photovoltaic (PV) anodes in hybrid thermionic devices for the conversion of thermal‐to‐electrical energy. Because PV anodes integrated in thermionic converters can operate at temperatures higher than room temperature, in this study, X‐ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS) were used to investigate the temperature dependence up to 300°C of the chemical and physical properties of BaFx thin‐films, deposited on gallium arsenide and silicon, that represent possible candidates for PV anodes. A correlation between chemical composition and work function reduction by 0.5 ± 0.1 eV for the thin films on both GaAs and Si has been found as a function of temperature from room temperature to 300°C. According to XPS analyses, this effect can be ascribable to the thermal desorption of the first contaminated layers of BaFx coatings. [ABSTRACT FROM AUTHOR]

Thin films based on scandium oxide (Sc2O3) were deposited on silicon substrates to investigate the thickness effect on the reduction of work function. X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), energy dispersive X-ray reflectivity (EDXR), atomic force microscopy (AFM), and ultraviolet photoelectron spectroscopy (UPS) measurements were performed on the films deposited by electron-beam evaporation with different nominal thicknesses (in the range of 2–50 nm) and in multi-layered mixed structures with barium fluoride (BaF2) films. The obtained results indicate that non-continuous films are required to minimize the work function (down to 2.7 eV at room temperature), thanks to the formation of surface dipole effects between crystalline islands and substrates, even if the stoichiometry is far from the ideal one (Sc/O = 0.38). Finally, the presence of BaF2 in multi-layered films is not beneficial for a further reduction in the work function. [ABSTRACT FROM AUTHOR]

Thin films of barium fluorides with different thicknesses were deposited on GaAs substrate by electron beam evaporation. The aim of the work was to identify the best growth conditions for the production of coatings with a low work function suitable for the anode of hybrid thermionic‐photovoltaic (TIPV) devices. The chemical composition and work function φ of the films with different thicknesses were investigated by X‐ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). The lowest value of φ = 2.1 eV was obtained for the film with a thickness of ~2 nm. In the valence band spectra of the films at low kinetic energy, near the cutoff, a characteristic peak of negative electron affinity was present. This effect contributed to a further reduction of the film's work function. [ABSTRACT FROM AUTHOR]