Breaking thermoelectric (TE) trade-off relationship is a dreaming task to maximum TE performance of polymeric semiconductors. Existing efforts focuses on designing high mobility semiconductors and achieving ordered molecular doping, ignoring the critical role of molecular orientation on TE conversion. Here, we report the achievement of ZT to 0.40 by fine-tuning molecular orientation of one diketopyrrolopyrrole-based polymer (DPP-BTz). The films with bimodal molecular orientation not only yield superior doping efficiency by increasing lamellar spacing, but also result in increased splitting between the Fermi energy and the transport energy to enhance thermopower. It therefore contributes to simultaneous improvement of Seebeck coefficient and electrical conductivity in an unexpected way. More importantly, the bimodal film exhibits a maximum power factor of up to 346 μW m−1 K−2, more than 400% higher than that of unimodal films. The result indicates great potential of molecular orientation engineering in polymeric semiconductors for developing state-of-the-art OTE materials.

Triggering ZT to 0.40 by engineering orientation in one polymeric semiconductor

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