Band gap temperature-dependence of close-space sublimation grown Sb2Se3 by photo-reflectance

Abstract

The candidate photovoltaic absorber antimony selenide Sb2Se3 has been prepared by the commercially attractive close-space sublimation method. Structure, composition, and morphology are studied by x-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy. Large rhubarb-like grains favorable for photovoltaics naturally develop. The temperature-dependence of the direct band gap is determined by photoreflectance between 20 and 320 K and is well described by the Varshni and Bose–Einstein relations, blue-shifting with decreasing temperature from 1.18 to 1.32 eV. The 300 K band gap matches that seen in high quality single-crystal material, while the 0 K gap is consistent with that found in first-principles calculations, further supporting the array of beneficial photovoltaic properties indicated for this material.

The complex defect chemistry of antimony selenide

“…This method has been previously shown to give highly accurate structural properties in comparison with experiment, and also results in a predicted band gap that lies within 10 meV of a 0 K Varshni t to experimental measurements. 8,26 Defect calculations were also performed using the HSE06+D3 method on a 1 Â 3 Â 1 supercell (60 atoms) with a G centered 2 Â 2 Â 2 kpoint mesh and a plane-wave energy cutoff of 350 eV. All structures were optimized until the forces on each atom were below 0.02 eVÅ À1 .…”

Chemical etching of Sb2Se3 solar cells: surface chemistry and back contact behaviour

“…These planes are representative of nanoribbons lying at 37°, 44°, 46°and 0°from normal to the substrate for the (211), (221), (301) and (002) planes respectively. Growth of nanoribbons normal to the substrate surface would be expected to optimise both vertical conduction along the nanoribbon axes and also increase the fraction of van der Waalsbonded rather than covalent-bonded grain boundaries, both of which are expected to be beneficial to photovoltaic performance [2,4]. Even the ∼45°angle of the (221) and (301) planes from normal is not expected to impede carrier transport due to the size of the grains in this material.…”

“…Even the ∼45°angle of the (221) and (301) planes from normal is not expected to impede carrier transport due to the size of the grains in this material. It is reasonable to assume that the majority of the grains, and therefore the nanoribbons, span from the bottom to the top of the film [2,11]. There is a small difference in the peak at 26.6°, however this is attributed to an additional Sb 2 Se 3 (021) orientation [2] and is therefore not indicative of any significant change at the surface.…”

“…J-V-T analysis was carried out on all CSS deposited Sb 2 Se 3 devices in order to determine the magnitude of f b . R s values were measured in the dark via the slope method for a range of temperatures (250-350K) for all devices prior to fitting them using equation (2). The fits can be found in figure 8 and the results of the fitting are shown in table 5.…”

“…Antimony selenide (Sb 2 Se 3 ) is a rapidly developing inorganic material which shows great promise within the field of thin film photovoltaics (PV); it is a stable, binary V-VI compound with a direct band gap of 1.18 eV [1,2] -well suited for use in PV. Its absorption coefficient is >10 5 cm −1 and the constituent materials are cheap and abundant [1] with low toxicity [3].…”