High Seebeck Coefficient in Mixtures of Conjugated Polymers

A universal method to obtain record‐high electronic Seebeck coefficients is demonstrated while preserving reasonable conductivities in doped blends of organic semiconductors through rational design of the density of states (DOSs). A polymer semiconductor with a shallow highest occupied molecular orbital (HOMO) level‐poly(3‐hexylthiophene) (P3HT) is mixed with materials with a deeper HOMO (PTB7, TQ1) to form binary blends of the type P3HT x :B 1‐ x (0 ≤ x ≤ 1) that is p‐type doped by F 4 TCNQ. For B = PTB7, a Seebeck coefficient S = 1100 µV K −1 with conductivity σ = 0.3 S m −1 at x = 0.10 is achieved, while for B = TQ1, S = 2000 µV K −1 and σ = 0.03 S m −1 at x = 0.05 is found. Kinetic Monte Carlo simulations with parameters based on experiments show good agreement with the experimental results, confirming the intended mechanism. The simulations are used to derive a design rule for parameter tuning. These results can become relevant for low‐power, low‐cost applications like (providing power to) autonomous sensors, in which a high Seebeck coefficient translates directly to a proportionally reduced number of legs in the thermogenerator, and hence in reduced fabrication cost and complexity.