Compositional dependence of the optical properties of amorphous Sb2Se3−xSx thin films

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

“…22,23 While the precursory CdS/Sb 2 Se 3 layout (inherited from CdTe) allows the detrimental diffusion of Cd atoms across the junction interface, 5 performance improves with TiO 2 /Sb 2 Se 3 or ZnO/Sb 2 Se 3 architectures 5,24 and with a supplementary PbS hole-transport layer. 6 Prior Sb 2 Se 3 synthesis routes have included thermal evaporation, 3,5,8,18,25,26 chemical bath deposition, 12,26 Bridgman method, 9 solution or spin-coating, 12 RF sputtering, 26 and spray-deposition or pyrolysis. 25,26 This paper reports large Sb 2 Se 3 crystal grains grown by close-space sublimation (CSS), perhaps the simplest physical vapor deposition method.…”

“…6 Prior Sb 2 Se 3 synthesis routes have included thermal evaporation, 3,5,8,18,25,26 chemical bath deposition, 12,26 Bridgman method, 9 solution or spin-coating, 12 RF sputtering, 26 and spray-deposition or pyrolysis. 25,26 This paper reports large Sb 2 Se 3 crystal grains grown by close-space sublimation (CSS), perhaps the simplest physical vapor deposition method. CSS is highly attractive to commercial PV vendors and is often favored for CdTe cell fabrication (including champion cells).…”

“…Specific advantages include low-costs, high deposition rates (e.g., several microns of CdTe within minutes), configuration versatility, and ease of scaling-up to meet production targets. 27 Despite the interest in Sb 2 Se 3 , considerable variance is seen in reports on the nature and magnitude of the band gap, which is variously claimed to be either indirect, ranging from 1.0 to 1.5 eV (either allowed 8,10,11,25,26 or forbidden 9 ), or direct 8,11 ranging from 1.2 to 1.9 eV. The fundamental gap is generally considered to be indirect with a direct gap lying at ∼0.1 eV to higher energy, 8 leading to very strong optical absorption: highly desirable in a PV absorber; in contrast, silicon has rather weak absorption until the direct onset at 3.2 eV.…”

“…Variable material quality is another key factor complicating band gap assessment. Amorphous material is often reported [7][8][9]11,18,25,26 in low-temperature Sb 2 Se 3 deposition and always has a higher gap than crystalline material. An amorphous-to-crystalline transition 7,8,11,16,26,31 occurs upon annealing above 200 • C, yet while crystalline material is easily detected by x-ray diffraction, amorphous phase fractions are more difficult to quantify.…”

“…Amorphous material is often reported [7][8][9]11,18,25,26 in low-temperature Sb 2 Se 3 deposition and always has a higher gap than crystalline material. An amorphous-to-crystalline transition 7,8,11,16,26,31 occurs upon annealing above 200 • C, yet while crystalline material is easily detected by x-ray diffraction, amorphous phase fractions are more difficult to quantify. In non-stoichiometric material, the band gap is reported to increase quadratically with increasing Se content 26 or in the presence of an oxygen impurity 5,7 (perhaps differing from the Fd3m Sb 2 O 3 phase) which is removed after annealing in N 2 and Se vapor at 300 • C. Allowing also for potential polycrystalline disorder, each of these factors likely necessitates the consideration of an Urbach tail in any fit to the absorption onset.…”