Enhancement of thermoelectric figure of merit of Bi₂Te₃ using carbon dots

Thermoelectric (TE) energy harvesters are multi-material solid-state devices that convert heat (i.e. a thermal gradient) directly into electric potential. Currently, the biggest challenge limiting the applications of thermoelectric devices is the low conversion efficiency (<10%). To achieve higher thermoelectric efficiency, electrical conductivity and Seebeck coefficient of thermoelectric materials must be maximized allowing the flow of charge carriers and thermal conductivity must be minimized keeping high temperature gradient between hot and cold sides. These properties are strongly coupled to each other. In other words, improving one property deteriorates the other. In nanoscale however, manipulation of matter at the atomic level can decouple these properties. Nanoengineering is therefore considered to be the only remedy for the low conversion efficiency of thermoelectric materials. Current nanomanipulation techniques focus only on reducing thermal conductivity by scattering heat carrying phonons with nanoscale artifacts. We have observed that doping thermoelectric material with carbon quantum dots (size < 5 nm) tremendously increased electrical conductivity and thermoelectric power. In the control experiments using carbon powder (same chemical arrangement but larger scale, <100 nm), we did not observe any increase in thermal power density evidencing the nanomanipulation of material properties using carbon quantum dots. Doping thermoelectric materials with carbon quantum dots has high potential due to the quantum enhancement effects on electrical properties of and needs to be further investigated for the design of novel nanocomposite materials with superior thermoelectrical properties.