Optimal array alignment to deliver high performance in flexible conducting polymer‐based thermoelectric devices

• High charge mobility and optimal oxidation level leads to high power factor;. • Identification of the optimal distance between two adjacent TE arrays for devices;. • A flexible thermoelectric device shows a power density of 1.21 µW∙cm −2 . Flexible thermoelectric devices (F-TEDs) show great potentials to be applied in curved surface for power generation by harvesting low-grade energy from human body and other heat sources. However, their power generation efficiency is constrained by both unsatisfactory constituent materials performance and immature device design. Here, we used an optimal alignment of vertically-aligned poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) arrays to assemble a 2.7 × 3.2 cm 2 F-TEDs, exhibiting a maximum power output of 10.5 µW. Such a high performance can be ascribed to the outstanding power factor of 198 µW m −1 K −2 by the synergetic effect of both high charge mobility and optimal oxidation level and the optimized array alignment that maximizes the temperature difference utilization ratio across the TE legs. Particularly, optimized leg distance of 6 mm and leg length of 12 mm are determined to realize a high temperature difference utilization ratio of over 95% and a record-high output power density of 1.21 µW cm −2 under a temperature difference of 30 K. Further, reliable bending (1000 cycles) and stability (240 h) tests indicate the outstanding mechanical robustness and environmental stability of the developed F-TEDs. This study indicates our reasonable device design concept and facile material treatment techniques secure high-performance F-TEDs, serving as a reference for other flexible energy harvesting devices with wide practical applications.