Advances in bismuth-telluride-based thermoelectric devices: Progress and challenges

By effectively converting waste heat into electricity,thermoelectric materials and devices can provide an alternative approach to tackle the energy crisis.Amongst thermoelectric materials,bismuth telluride(Bi_(2)Te_(3))and its derivatives exhibit high figure of merit ZT values in the near-room-temperature region and show great potential for application in thermoelectric devices.Considering the rapid development of Bi_(2)Te_(3)-based thermoelectric materials and their devices in the last few years,a short and systematic review is much needed.Here,we sum-marize the novel designs,properties,and applications of Bi_(2)Te_(3)-based thermoelectric devices in different contexts,including wearable,portable,implantable,and cross-disciplinary applications.The challenges and outlook for Bi_(2)Te_(3)-based thermoelectric devices are also considered.This work will guide the future development of Bi_(2)Te_(3)-based thermoelectric devices that target broader and more practical applications.

Optimal array alignment to deliver high performance in flexible conducting polymer-based thermoelectric devices

Flexible thermoelectric devices(F-TEDs)show great potentials to be applied in curved surface for power generation by harvesting low-grade energy from human body and other heat sources.However,their power generation efficiency is constrained by both unsatisfactory constituent materials performance and immature device design.Here,we used an optimal alignment of vertically-aligned poly(3,4-ethylenedioxythiophene)polystyrene sulfonate(PEDOT:PSS)arrays to assemble a 2.7×3.2 cm^(2)F-TEDs,exhibiting a maximum power output of 10.5μW.Such a high performance can be ascribed to the outstanding power factor of 198μW m^(-1)K^(-2)by the synergetic effect of both high charge mobility and optimal oxidation level and the optimized array alignment that maximizes the temperature difference utilization ratio across the TE legs.Particularly,optimized leg distance of 6 mm and leg length of 12 mm are determined to realize a high temperature difference utilization ratio of over 95%and a record-high output power density of 1.21μW cm^(-2)under a temperature difference of 30 K.Further,reliable bending(1000 cycles)and stability(240 h)tests indicate the outstanding mechanical robustness and environmental stability of the developed F-TEDs.This study indicates our reasonable device design concept and facile material treatment techniques secure high-performance F-TEDs,serving as a reference for other flexible energy harvesting devices with wide practical applications.

Enhancing thermoelectric performance of SrFBiS_(2-x)Se_(x) via band engineering and structural texturing

SrFBiS_(2) is a quaternary n-type semiconductor with rock-salt-type BiS_(2) and fluorite-type SrF layers alternately stacked along the c axis.The tunability of the crystal and electronic structures as well as the intrinsically low thermal conductivity make this compound a promising parent material for thermo-electric applications.In the current work,we show that alloying of Se and S in SrFBi_(S) 2 reduces the optical band gap with the second conduction band serving as an electron-transport medium,simultaneously increasing the electron concentration and effective mass.In addition,the raw material Bi_(2)Se_(3) is shown to act as liquid adjuvant during the annealing process,favoring preferred-orientation grain growth and forming strengthen microstructural texturing in bulk samples after hot-pressed sintering.Highly ordered lamellar grains are stacked perpendicular to the pressure direction,leading to enhanced mobility along this direction.The synthetic effect results in a maximum power factor of 5.58 μm W cm^(-1) K^(-2) at 523 K for SrFBiSSe and a peak zT=0.34 at 773 K,enhancements of 180%compared with those of pristine SrFBiS_(2).