Organic Thermoelectrics

Thermoelectric (TE) materials are a class of materials that can be used to generate electricity from waste heat. For practical TE applications, both p-type and n-type materials must exhibit comparable figures of merit, in order to operate in tandem in a TE generator device. However, n-type materials have so far lagged behind p-type materials. Molecular doping is the key, limiting process to enhancing the performance of n-type materials. It has been demonstrated that n doping efficiency can be increased by lowering the energy of the LUMO level and improving host dopant compatibility. These are, fundamentally, synthetic challenges and we aim to address them as such. In this contribution, we will present our strategies for designing and synthesizing new polymers and dopants to address key properties systematically.<br/>The high doping levels required to maximize performance and the differences in polarity between the host backbone, pendant groups, and ionized dopant molecules can drive deleterious phase separation within the doped film. These challenges can be overcome by tuning the doping concentration and designing pendant groups that interact with and control the dispersion of polar dopants such as 1,3-dimethyl-2-phenylbenzimidozoline (DMBI). Improving dopant solubility will lead to uniformity of the films, higher doping efficiency, and increased conductivity. <br/>The energy of the LUMO (conduction band) of the host polymer also plays an important role in increasing doping efficiency in polymeric n-type materials. Manipulating this energy can be achieved by tuning the electronic structure of conjugated polymers. However, electron transfer between the host polymer and the dopant can also be facilitated by introducing electron-rich donor moieties in the dopant, which is why we approach the synthetic challenges to both simultaneously.