Wong, Z. M., Deng, T., Shi, W., Wu, G., &amp; Yang, S.-W. (2020). Strain Effects on the n-Type Thermoelectric Performance of the Small-Molecule Organic Semiconductor 2-5-Difluoro-7,7,8,8-Tetracyanoquinodimethane. ACS Applied Energy Materials, 3(10), 10174–10182. doi:10.1021/acsaem.0c01875
Over the last few years, small-molecule organic semiconductors have been garnering increasing research interest as flexible electronic materials thanks to their abundance, ease of processing, high purity, and low thermal conductivity. In this work, we evaluate in detail the thermoelectric (TE) properties of the small-molecule organic semiconductor 2-5-difluoro-7,7,8,8-tetracyanoquinodimethane (F2-TCNQ) by first-principles calculations and the Boltzmann transport equation. Upon optimal n-doping, a peak power factor of 566 μW m–1 K–2 can be achieved at room temperature, attributed to the band-like three-dimensional (3D) intermolecular electron transport from the efficient overlapping and delocalization of the lowest unoccupied molecular orbitals (LUMOs), which results in high electron mobility and a favorable power factor. Coupled with a low thermal conductivity, this results in an outstanding thermoelectric figure-of-merit zT of 0.46. Furthermore, the zT is predicted to enhance tremendously by up to 120% (0.77) and 50% (0.65) upon application of 5% interlayer tensile and compressive strains, respectively, due to strain interplaying of the power factors and thermal conductivities. These findings not only showcase the potential outstanding TE properties of F2-TCNQ but also indicate strain engineering to be a viable approach toward the enhancement of TE performance, paving the way to methodized screening, identification, and assessment of other analogously layered small organic molecular materials for potentially high-performing TE applications.
This research / project is supported by the A*STAR - Pharos Programme
Grant Reference no. : 152720024