Improving the Thermoelectric Properties of 2,7-Dioctyl[1]Benzothieno[3,2-b][1]Benzothiophene-based Organic Semiconductors by Isotropic Strain

Ziman Wang,1,2#

Ming Yang,1,2#

Qinglong Jiang,3

Kun Zheng,4

Yongmei Ma,4

Hang Zhang1,2*Email

1Institute of Engineering Thermophysics, Chinese Academy of Sciences, Beijing 100190, China

2University of Chinese Academy of Sciences, Beijing 100049, China

3Department of Chemistry and Physics, University of Arkansas, Pine Bluff, Arkansas 71601, USA.

4Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China

Abstract

The effect of isotropic strain on the band structures and thermoelectric properties of 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) modified with hydroxyl (–OH), amino (–NH2), and methyl (–CH3) groups at room temperature have been investigated by first-principles calculations. We found that isotropic strain modified the Fermi levels and bandgaps of the C8-BTBT-based organic semiconductors. The variations of the dimensionless figure of merit (zT) values of the N-type semiconductors are greater than those of the P-type semiconductors. The thermoelectric properties were calculated using the BoltzTraP code. The results show that there is an optimal carrier concentration to give the maximum zT value of the C8-BTBT-based organic semiconductor. The maximum zT value of the N-type semiconductor is 0.41 for OH-modified C8-BTBT. For the P-type semiconductor, the maximum zT value is 0.36 for CH3-modified C8-BTBT. We also found that NH2-modified C8-BTBT has poor thermoelectric properties, which means that the –NH2 group may not be the optimal choice for C8-BTBT in thermoelectric applications.

Improving the Thermoelectric Properties of 2,7-Dioctyl[1]Benzothieno[3,2-b][1]Benzothiophene-based Organic Semiconductors by Isotropic Strain