Theoretical Study On The Thermoelectric Transport Properties Of Organic Molecular Crystals Bis-Dithienothiophene

With the rapid development in economy, more and more energy is consumed. But about seventy percent of the consumed energy is wasted, mostly in terms of waste heat.Meanwhile, the traditional energy is limited and will be exhausted one day. In order to save the energy crisis, new energy industry rises gradually, looking for new, green,sustainable energy. Within this background, thermoelectric materials receive more and more attention. The reason is that they can realize energy conversion from heat to electricity directly. For instance, they can be made into thermoelectric generator. In reverse, they can also be made into thermoelectric cooler.In the beginning, the main attention is paid to the study of three-dimensional inorganic semiconductor materials, for instance, Bi2Te3, PbTe, SnSe, Si, Ge, perovskites and so on. In recent years, with the development of nanotechnology and in-depth studies of electronic, and phononic transport in the nanoscale, studies on thermoelectric properties of low-dimensional materials have become more and more popular. The energy conversion efficiency of thermoelectric materials depends on the thermoelectric figure of merit ZT. To achieve the commercial purpose, ZT should be larger than 3.Near the Fermi surface, sharp change of electron density of states results in large Seebeck coefficients, while phonon glass material has low phonon thermal conductivity.So, low-dimensional electronic and glassy phononic transport are two important ingredients to improve the efficiency of thermoelectric materials, and they form two branches of the thermoelectric research. We can focus either on controlling electronic transport in low-dimensional, or on taking use of phonon engineering in the bulk to improve ZT. Recent work has combined the two approaches well.In this paper, we propose to employ the low-dimensional electronic structure in bulk phonon-glass crystals as a way to increase the thermoelectric efficiency. We take organic molecule Bis-Dithienophene as an example, putting forward the idea that we can improvethe thermoelectric transport by utilizing the low-dimensional band structure, and keep the low thermal conductivity of the molecular crystal at the same time. Through first-principles electronic structure calculation and theoretical analysis, we approve the feasibility of the idea. Without any optimization of the material parameters, we obtained a maximum room-temperature ZT of 1.48. Meanwhile, we believe that this idea should be equally applicable to inorganic materials. Even through organic thermoelectric materials have the advantages of the flexible, cheap, non-toxic, light and so on, but the related theory is not yet mature. Many organic thermoelectric materials have low ZT. It is a rather new direction. We hope that our work can attract more researchers to get involved in this research direction.