I₂–II–IV–VI₄ (I = Cu, Ag; II = Sr, Ba; IV = Ge, Sn; VI = S, Se): Chalcogenides for Thin-Film Photovoltaics

Abstract

Recent work has identified a non-zinc-blendetype quaternary semiconductor, Cu 2 BaSnS 4−x Se x (CBTSSe), as a promising candidate for thin-film photovoltaics (PVs). CBTSSe circumvents difficulties of competing PV materials regarding (i) toxicity (e.g., CdTe), (ii) scarcity of constituent elements (e.g., Cu(In,Ga)(S,Se) 2 /CdTe), and (iii) unavoidable antisite disordering that limits further efficiency improvement (e.g., in Cu 2 ZnSnS 4−x Se x ). In this work, we build on the CBTSSe paradigm by computationally scanning for further improved, earth-abundant and environmentally friendly thinfilm PV materials among the 16 quaternary systems I 2 −II− IV−VI 4 (I = Cu, Ag; II = Sr, Ba; IV = Ge, Sn; VI = S, Se). The band structures, band gaps, and optical absorption properties are predicted by hybrid density-functional theory calculations. We find that the Ag-containing compounds (which belong to space groups I222 or I4̅ 2m) show indirect band gaps. In contrast, the Cu-containing compounds (which belong to space group P3 1 /P3 2 and Ama2) show direct or nearly direct band gaps. In addition to the previously considered Cu 2 BaSnS 4−x Se x system, two compounds not yet considered for PV applications, Cu 2 BaGeSe 4 (P3 1 ) and Cu 2 SrSnSe 4 (Ama2), show predicted quasi-direct/ direct band gaps of 1.60 and 1.46 eV, respectively, and are therefore most promising with respect to thin-film PV application (both single-and multijunction). A Cu 2 BaGeSe 4 sample, prepared by solid-state reaction, exhibits the expected P3 1 structure type. Diffuse reflectance and photoluminescence spectrometry measurements yield an experimental band gap of 1.91(5) eV for Cu 2 BaGeSe 4 , a value slightly smaller than that for Cu 2 BaSnS 4 .

Tunable internal quantum well alignment in rationally designed oligomer-based perovskite films deposited by resonant infrared matrix-assisted pulsed laser evaporation

“…All three band alignments are expected to exist within the AEnTPbX 4 family. To facilitate rational selection of COP compounds exhibiting the three distinct behaviors, we extend the demanding hybrid spin-orbit-coupled DFT [33][34][35][36][37][38][39][40][41] calculations of Liu et al 3 with newly-predicted band alignments in the AEnTPbX 4 family with n = 1-5, X = Cl, Br, I ( Fig. S1 and Table S1, ESI †).…”

“…In traditional inorganic semiconductors with similar band gaps, we would expect this choice to systematically underestimate the fundamental gap by approximately 0.3 eV. 39…”

Promising quaternary chalcogenides as high-band-gap semiconductors for tandem photoelectrochemical water splitting devices: A computational screening approach

“…As a result of copper substitution with silver, the amount of band tailing decreases indicating less structural disorder. These experiments indicate that there is a great potential in engineering the properties of CZTS-like materials and theoretical attempts are already being made to expand the materials space beyond CZTS for optoelectronic applications [37,38].…”

Recent Progress on Cu2BaSn(SxSe1–x)4: From Material to Solar Cell Applications

“…Zhu et al reported the optical properties of Cu 2 BaSn(S x Se 1-x ) 4 , including the optical absorption coefficients of Cu 2 BaSnS 4 (P3 1 ) and Cu 2 BaSnSe 4 (Ama2). [76] The absorption coefficient of Cu 2 BaSnS 4 (P3 1 ) is isotropic in this region, similar to that of CZTSSe. However, the absorption coefficient of Cu 2 BaSnSe 4 with a much lower bandgap is much higher than that of Cu 2 BaSnS 4 when the spectral region is up to 2.5 eV.…”