Enhanced Thermoelectric Efficiency via Orthogonal Electrical and Thermal Conductances in Phosphorene

Abstract

Thermoelectric devices that utilize the Seebeck effect convert heat flow into electrical energy and are highly desirable for the development of portable, solid state, passively powered electronic systems. The conversion efficiencies of such devices are quantified by the dimensionless thermoelectric figure of merit (ZT), which is proportional to the ratio of a device's electrical conductance to its thermal conductance. In this paper, a recently fabricated two-dimensional (2D) semiconductor called phosphorene (monolayer black phosphorus) is assessed for its thermoelectric capabilities. First-principles and model calculations reveal not only that phosphorene possesses a spatially anisotropic electrical conductance, but that its lattice thermal conductance exhibits a pronounced spatial-anisotropy as well. The prominent electrical and thermal conducting directions are orthogonal to one another, enhancing the ratio of these conductances. As a result, ZT may reach the criterion for commercial deployment along the armchair direction of phosphorene at T = 500 K and is close to 1 even at room temperature given moderate doping (∼2 × 10(16) m(-2) or 2 × 10(12) cm(-2)). Ultimately, phosphorene hopefully stands out as an environmentally sound thermoelectric material with unprecedented qualities. Intrinsically, it is a mechanically flexible material that converts heat energy with high efficiency at low temperatures (∼300 K), one whose performance does not require any sophisticated engineering techniques.

Promising thermoelectric properties of phosphorenes

“…Due to such superior electronic transport properties and relatively low k L (compared with the κ of graphene, 2000 −5000Wm −1 K −1 [34]), black-P has been suggested as a potential material for new generation nano thermoelectric applications. As a matter of fact, the room temperature thermoelectric figure of merit (ZT) of two-dimensional and quasione-dimensional (ribbon) black-P have been estimated to be as high as 1.0 [28] and 6.4 [35] respectively, using the semiclassical Boltzmann theory within the relaxation time approximation. In addition, a remarkable increase in the Seebeck coefficient and electrical conductivity of black-P with strain induced band convergence, which leads to a maximum room temperature ZT value ∼2.1 [36] have also been reported using the same method.…”

Two-dimensional flexible nanoelectronics

“…The expanding portfolio of atomic sheets illustrated in Fig. 1a currently include the archetypical 2D crystal graphene 3-14 , transition metal dichalcogenides (TMDs) 1,2,15-21 , diatomic hexagonal boron nitride (h-BN) 3,[22][23][24][25] , and emerging monoatomic buckled crystals collectively termed Xenes, which include silicene 2,26,27 , germanene 2 and phosphorene [28][29][30][31] . These materials are considered 2D because they represent the thinnest unsupported crystalline solids that can be realized, possess no dangling surface bonds and show superior intralayer (versus interlayer) transport of fundamental excitations (charge, heat, spin and light).…”

Multipurpose Black-Phosphorus/hBN Heterostructures

“…Moreover, the higher carrier mobilities (1, 000 cm 2 /Vs) 10 compared to TMDC monolayers, the strongly anisotropic electronic and optical properties, [11][12][13][14][15] as well as the robustness under elastic strain [16][17][18] have already ensured novel uses of BP in electronic, 9,10,12,19,20 photonic, [21][22][23] and thermoelectric 24,25 applications.…”