Lone pair driven anisotropy in antimony chalcogenide semiconductors

Abstract

Antimony sulfide (Sb 2 S 3 ) and selenide (Sb 2 Se 3 ) have emerged as promising earth-abundant alternatives among thin-film photovoltaic compounds. A distinguishing feature of these materials is their anisotropic crystal structures, which are composed of quasi-one-dimensional (1D) [Sb 4 X 6 ] n ribbons. The interaction between ribbons has been reported to be van der Waals (vdW) in nature and Sb 2 X 3 are thus commonly classified in the literature as 1D semiconductors. However, based on first-principles calculations, here we show that inter-ribbon interactions are present in Sb 2 X 3 beyond the vdW regime. The origin of the anisotropic structures is related to the stereochemical activity of the Sb 5s lone pair according to electronic structure analysis. The impacts of structural anisotropy on the electronic, dielectric and optical properties are further examined, including the presence of higher dimensional Fermi surfaces for charge carrier transport. Our study provides guidelines for optimising the performance of Sb 2 X 3 -based solar cells via device structuring based on the underlying crystal anisotropy.

Low Carrier Effective Masses in Photoactive Sr2Sb2O2Q3 (Q = S, Se): The Role of the Lone Pair

“…Another example in chalcogenides are the well-known Sb 2 S 3 and Sb 2 Se 3 semiconductors, which were also theoretically studied for lone pair-related anisotropic effects (effective masses and mobility) to provide guidelines for using their features to design efficient solar cells devices. 57 Similar effects were also observed for Sb-based compounds, 61 19 and a Bi-based compound with a 6s 2 stereoactive lone pair. 62 To quantify this stereochemical activity, a universal method described by Hu et al 63,64 was adopted to calculate the ratio of the stereochemical activity R SCA , which involves integrating the PDOS of Sb states from a specified energy level (the point where the intensity of Sb s and Sb p is equivalent) to the Fermi level (set at 0).…”

“…Recently, theoretical studies have been reported for reduced main group cations (in oxides), such as the lone pair cation Sn 2+ (discussed later, ref ), where the high mobility of the charge carriers is mostly related to the lone pair states and the overlap between the s orbital of the lone pair cation and the anions states. Another example in chalcogenides are the well-known Sb 2 S 3 and Sb 2 Se 3 semiconductors, which were also theoretically studied for lone pair-related anisotropic effects (effective masses and mobility) to provide guidelines for using their features to design efficient solar cells devices . Similar effects were also observed for Sb-based compounds, such as Sr 6 Cd 2 Sb 6 S 7 O 10 and Sr 6 Cd 2 Sb 6 Se 7 O 10 , and a Bi-based compound with a 6s 2 stereoactive lone pair …”

“…A similar Sb 5s contribution to the top of the valence band was also observed for several antimony-based compounds, including Sr 6 Cd 2 Sb 6 S 10 O 7 oxysulfide; , α-Sb 2 O 3 , β-Sb 2 O 3 , γ-Sb 2 O 3 , α-Sb 2 O 4 and β-Sb 2 O 4 oxides; and Sb 2 S 3 and Sb 2 Se 3 chalcogenide semiconductors . This Sb 5s– Q n p ( Q = O, S, Se) hybridization plays a key role in reducing the band gap into the visible range.…”

Impact of metastable defect structures on carrier recombination in solar cells

“…Bi, Sb and Sn-based materials), 1,40 low crystal symmetry (e.g. Sb 2 X 3 ) 41,42 and/or compositional complexity (e.g. multinary compounds such as CZTS and double perovskites) [43][44][45] are likely to manifest local minima on defect energy surfaces.…”