Enhanced Thermoelectric Efficiency via Orthogonal Electrical and Thermal Conductances in Phosphorene

TL;DR

This paper demonstrates that phosphorene, a 2D semiconductor, exhibits high thermoelectric efficiency at low temperatures due to its orthogonal electrical and thermal conductances, making it promising for practical energy conversion applications.

Contribution

It reveals that phosphorene's anisotropic conductances enhance thermoelectric performance, achieving high ZT values without complex engineering.

Findings

ZT reaches 2.5 along armchair direction at 500K

ZT exceeds 1 at room temperature with moderate doping

Phosphorene is mechanically flexible and environmentally friendly

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. High ZT (>2) has been achieved in materials via all-scale hierarchical architecturing. This efficiency holds at high temperatures (700K~900K) but quickly diminishes at lower temperatures. 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 that phosphorene possesses spatially-anisotropic electrical and thermal conductances. The prominent electrical and thermal conducting directions are orthogonal to one another, enhancing the ratio of these conductances. As a result, ZT can reach 2.5 (the criterion for commercial deployment) along the armchair direction of phosphorene at T=500K and is greater than 1 even at room temperature given moderate doping (~2 x 10^16 m-2). Ultimately, phosphorene 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 (~ 300K) - one whose performance does not require any sophisticated engineering techniques.