Enhancing Visible Light Absorption for Ferroelectric Sn₂P₂S₆ by Se Anion Substitution

Abstract

Ferroelectric (FE) semiconductors that simultaneously exhibit spectrally suitable band gaps and room temperature stable FE polarizations necessary for separation of photo-excited carriers have been extensively investigated for FE-photovoltaic (PV) applications. Di tin hexathiohypodiphosphate, Sn 2 P 2 S 6 , is one of the rare semiconducting FE materials. However, owing to the indirect nature of its energy band gap and relatively large direct band gap, FE Sn 2 P 2 S 6 absorbs only a small portion of the visible light spectrum. In the current work, we propose substitution of S by Se anion as an experimental feasible route to enhance the visible light absorption for FE Sn 2 P 2 S 6 . Using first-principles calculations, we demonstrate that the effective "band gap engineering" with respect to Se substitution concentration can be achieved in Sn 2 P 2 S 6(1−x) Se 6x solid solutions. Especially, Sn 2 P 2 S 4.5 Se 1.5 compound is predicted to be an indirect band gap semiconductor, with a direct band gap at Γ point even lower than that of BiFeO 3 , and meanwhile exhibits a stable ferroelectricity comparable with single-phase Sn 2 P 2 S 6 . As a result, the improved visible light absorption can be achieved in Sn 2 P 2 S 4.5 Se 1.5 compound, making Se-doped FE Sn 2 P 2 S 6 more suitable for PV applications.

Enhanced domain wall conductivity in photosensitive ferroelectrics Sn2P2S6 with full-visible-spectrum absorption

“…The intrinsic absorption edge (around 527 nm) of the SPS crystal is observed in the inset of Fig. 2a, corresponding to the direct band gap of about 2.35 eV, which is consistent with previous reports [24,25]. Usually, this band gap will limit the visible-spectrum absorption in the range of 300-527 nm.…”

Nonlayered Tin Thiohypodiphosphate Nanosheets: Controllable Growth and Solar-Light-Driven Water Splitting

“…This constrains the available choice in nonlayered 2D nanomaterials for various applications such as catalysis. Moreover, a nonlayered Sn 2 P 2 S 6 crystal is theoretically acknowledged to possess a suitable bandgap, 24,25 which holds great potential for photocatalytic H 2 generation under visible light illumination. Herein, we successfully synthesized nonlayered Sn 2 P 2 S 6 nanosheets with Pc monoclinic phase, which are further utilized as a photocatalyst to produce H 2 gas under solar light illumination from pure water.…”

“…This constrains the available choice in nonlayered 2D nanomaterials for various applications such as catalysis. Moreover, a nonlayered Sn 2 P 2 S 6 crystal is theoretically acknowledged to possess a suitable bandgap, , which holds great potential for photocatalytic H 2 generation under visible light illumination.…”

Quantum paraelectricity and induced ferroelectricity by germanium doping of (PbySn1–y)2P2S(Se)6 single crystals

“…SPS is the most prominent example of ferroelectric ternary phosphorus chalcogenide crystals represented by the general formula M 2 P 2 X 6 (where M is transition or post-transition carbon group p metals, X is chalcogenides). Moreover, optical measurements have proven Sn 2 P 2 S 6 as a semiconductor with a relatively narrow bandgap and promising photorefractive, photovoltaic, electrooptic and piezoelectric features [2,3]. Another feature, that makes them very attractive for the researchers, is an isovalent anion substitution into the crystal lattice producing series of (Pb y Sn 1-y ) 2 P 2 (Se x S 1-x ) 6 mixed crystals.…”