Modulation of thermoelectric performance of Cn-BTBT molecular junctions by engineering contact geometry
Bei Zhang, Xiaojiao Zhang, Shidong Zhang, Yunpeng Wang, Jiwei Dong, Yaoxing Sun, Fangping Ouyang, Mengqiu Long
Abstract
Organic molecular devices are promising candidates for thermoelectric applications. By using density functional theory combined with non-equilibrium Green’s function method, we have investigated the thermoelectric properties of a single-molecule junction, which is constructed by 2,7-dialkyl [1] benzothieno [3,2-b] [1] benzothiophene derivatives (Cn-BTBT) connected with zigzag graphene nanoribbon electrodes. It is found that the phonon thermal conductance decreases with the increase of alkyl edge branches due to the local resonance. And the thermoelectric performance can be enhanced significantly by substituting bithiophene or biphosphole bridge anchor groups. A good thermoelectric figure of merit about 0.56 can be obtained near Fermi level. Moreover, we also found that the molecular device can be changed from p-type into n-type by changing the contact points, resulting in the transformation of Seebeck coefficient from positive to negative.