Manipulating thermal and electronic transports in thermoelectric Bi$_2$Te$_3$ nanowires by porphyrin adsorption

Decoupling the electronic thermal and electrical conductivities is one of the limitations hindering a breakthrough in thermoelectric efficiency. After a conformal surface coating of bismuth telluride nanowires (Bi$_2$Te$_3$ NWs) by porphyrins, the thermal conductivity increases from 0.8 to 1.0 Wm$^{-1}$K$^{-1}$ at 300 K without any obvious change in electrical conductivity. Density Functional Theory (DFT) calculations assisted by Boltzmann Transport Equation (BTE) simulations of electronic transport properties indicate that the electronic thermal transport is enhanced by the depletion of surface charge carriers, which results in transition from metallic to semiconducting behavior. Thus, the adsorption of porphyrin onto the Bi$_2$Te$_3$ NWs layer suppresses the surface electronic conduction, resulting in thermal electronic conduction dictated by the bulk of the NW. The results mean that electronic thermal transport can be decoupled from the electrical conductivity by changing the density of surface states on Bi$_2$Te$_3$ NWs