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

The effect of isotropic strain on the band structures and thermoelectric properties of 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C 8 -BTBT) modified with hydroxyl ( – OH), amino ( – NH 2 ), and methyl ( – CH 3 ) groups at room temperature have been investigated by first-principles calculations. We found that isotropic strain modified the Fermi levels and bandgaps of the C 8 -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 ( N ) to give the maximum zT value of the C 8 -BTBT-based organic semiconductor. The maximum zT value of the N-type semiconductor is 0.41 for OH-modified C 8 -BTBT. For the P-type semiconductor, the maximum zT value is 0.36 for CH 3 -modified C 8 -BTBT. We also found that NH 2 -modified C 8 - BTBT has poor thermoelectric properties, which means that the – NH 2 group may not be the optimal choice for C 8 -BTBT in thermoelectric applications.