Sb 5s² lone pairs and band alignment of Sb₂Se₃: a photoemission and density functional theory study

Abstract

The presence of a lone pair of 5s electrons at the valence band maximum (VBM) of Sb2Se3 and the resulting band alignments are investigated using soft and hard x-ray photoemission...

Hidden spontaneous polarisation in the chalcohalide photovoltaic absorber Sn2SbS2I3

“…1,32 One-dimensional atomic chain structures, exhibited by this (Fig. 1) and related materials such as Sb Se 3 , 35 BiOI 32 and SbSI, 29,30 can yield benign grain boundaries, greatly reducing charge-carrier recombination in polycrystalline absorber materials. 32,74 The small electronic band gap (E g ∼ 1.1 eV), wide con-duction and valence bands, and relatively small electron effective mass (m e = 0.29) also favour defect-tolerant behaviour in this material.…”

“…c. Maximum PV efficiency (η max ) as a function of film thickness, using the SLME 60 and Blank et al 61 estimates for the radiative limit (Q i = 1). MAPI (5.70 eV) 72 , SbSI (5.37 eV) 30 and Sb 2 Se 3 (5.13 eV), 35 and slightly larger than that of FaSnI 3 (4.88 eV) 73 -favouring the formation of shallow acceptor defects which are innocuous to PV performance. The substantial mixed ionic-covalent character and lattice polarisability in Sn 2 SbS 2 I 3 , discussed previously, results in a strong dielectric screening (ε x,y,z = [51.3, 18.2, 22.4]) that will limit the electrostatic interactions between defects and charge carriers, thus reducing the probability of carrier capture and trapmediated recombination.…”

“…Indeed, this dynamic stereochemical activ-ity of the Sb lone-pair is one of the primary driving factors behind the formation of the distorted, lower-symmetry Cmc2 1 polymorph -through a second-order Jahn-Teller instability, often observed in lone-pair chalcogenides. 22,[33][34][35] While all experimental works have reported the Cmcm crystal structure for Sn 2 SbS 2 I 3 , 9,10,12 Ibanez et al 10 noted that assignment of Sb to an 8f Wyckoff position (i.e. the Sb Wyckoff site in Cmc2 1 symmetry) with 50% occupancy, as opposed to the 4c site for Cmcm, gave a significant reduction in R-factor -a measure of agreement between the structure model and diffraction data 36 -from 0.105 to 0.066.…”

Ge 4s2 lone pairs and band alignments in GeS and GeSe for photovoltaics

“…22 This in turn implies that s orbitals will be relatively more prominent in HAXPES than in XPS spectra, as they will contribute a higher proportion of the total intensity at a higher incident photon energy, as found in previous studies on materials with ns 2 lone pairs. 9,17,23,24 HAXPES can also offer higher spectral resolution, but also has reduced surface sensitivity compared to XPS, so there are merits to using both techniques.…”

“…6,7 Lone pair materials An important feature of Sb 2 Se 3 is the contribution of the Sb 5s 2 lone pair to the valence band. 9 Materials with stereochemically active lone pairs are attracting growing interest because of the high power conversion efficiency of methyl-ammonium lead iodide (MAPI) solar cells. 1 There is growing evidence to suggest that a large part of the high performance of this material is due to the Pb 6s 2 lone pair, which is thought to underpin some of its desirable PV properties.…”