Few-Layer PdSe₂ Sheets: Promising Thermoelectric Materials Driven by High Valley Convergence

Abstract

Herein, we report a comprehensive study on the structural and electronic properties of bulk, monolayer, and multilayer PdSe 2 sheets. First, we present a benchmark study on the structural properties of bulk PdSe 2 by using 13 commonly used density functional theory (DFT) functionals. Unexpectedly, the most commonly used van der Waals (vdW)-correction methods, including DFT-D2, optB88, and vdW-DF2, fail to provide accurate predictions of lattice parameters compared to experimental data (relative error > 15%). On the other hand, the PBE-TS series functionals provide significantly improved prediction with a relative error of <2%. Unlike hexagonal two-dimensional materials like graphene, transition metal dichalcogenides, and h-BN, the conduction band minimum of monolayer PdSe 2 is not located along the high symmetry lines in the first Brillouin zone; this highlights the importance of the structure–property relationship in the pentagonal lattice. Interestingly, high valley convergence is found in the conduction and valence bands in monolayer, bilayer, and trilayer PdSe 2 sheets, suggesting promising application in thermoelectric cooling.

Two‐Dimensional Noble‐Metal Chalcogenides and Phosphochalcogenides

“…Hulliger determined a small band gap of 0.4 eV through resistivity measurements. Several theoretical studies predicted a (semi)metal‐to‐semiconductor transition for bulk 2 O ‐PdSe 2 as a result of the underestimation of the band gap with the PBE functional . This led to misinterpretations of optical absorbance spectra yielding a zero band gap for bulk PdSe 2 .…”

Palladium selenide as a broadband saturable absorber for ultra-fast photonics

“…A , A , B , and A g g g Raman active modes of PdSe 2 [78][79][80]. In general, the Raman characteristics of the PdSe 2 nanosheets should be studied as a comparison.…”

“…Reported results have proven that PdSe 2 exhibited several competitive excellent properties. Most importantly, PdSe 2 exhibits a thickness-dependent widetunable bandgap value, which can be narrowed from 1.3 eV for the monolayer to 0 eV for bulk [75][76][77][78][79][80][81]. Moreover, as is known that the thickness-dependent bandgap is not a unique property of PdSe 2 [82,83], the thickness-dependent bandgap is regarded as a commonality of two-dimensional materials.…”

“…Second, in comparison to other isotropic TMDCs, PdSe 2 has another unique property of pentagonal atomic structure in which Pd atoms coordinate with four Se atoms, forming a square backbone lattice ( Figure 1A and B). The waved Pd-Se layers are held together by van der Waals force with a distance of about 0.4 nm ( Figure 1C) [77][78][79][80][81]. Owing to the unique pentagonal atomic structure, in comparison with commonly used TMDs, PdSe 2 devices present a unique anisotropic response to external stimulations, which will provide opportunities for designing anisotropic photoelectric devices.…”

Zweidimensionale Edelmetallchalkogenide und ‐phosphochalkogenide

“…Hulliger hat eine kleine Bandlücke von 0.4 eV durch Widerstandsmessungen bestimmt. Mehrere theoretische Untersuchungen sagten einen (Halb)metall‐zu‐Halbleiter‐Übergang von Bulk zu Monolage vorher, wobei die Bandlücke des Bulk‐Materials aber durch das PBE‐Funktional unterschätzt wird . Das hat zur Fehlinterpretation von optischen Absorptionsspektren geführt, die einen metallischen Zustand für 2 O ‐PdSe 2 im Bulk ergeben haben .…”