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π‐Conjugated polymers can be manipulated at the molecular and thin‐film levels to strengthen thermoelectric performance. Herein, two distinctive polymers—PBDP‐T and PBDB‐T with respective outstanding Seebeck coefficient (S) and electrical conductivity (σ) are selected and their functional units are integrated to synthesize random terpolymers via the ′backbone sequence′ strategy. The resulting disordered π‐backbones of terpolymers however lead to an unsuccessful acquisition of high power factor (PF). Alternately, the ′film sequence′ strategy is utilized and representative high‐σ P2F and high‐S PTB7‐Th polymers are blended. Note that 3D conductive paths are generated in the blend films when the PTB7‐Th content falls between 35–80 wt%, which favors charge transportation and yields high σ. At an optimal 65 wt% PTB7‐Th, a maximum PF of 145.5 µW m−1 K−2 is obtained, far surpassing that of each parent polymer, which marks a breakthrough of the ′two‐phase combination′ rule. The peak PF achieved in medium PTB7‐Th content is attributed to the coexistence of bilayered and mixed morphologies, the former of which delivers slowly declining σ while the latter results in greatly elevated S with increasing PTB7‐Th. Given the notably lower thermal conductivity acquired in blend than neat polymers, the room‐temperature thermoelectric figure‐of‐merit as high as 0.15 is achieved. [ABSTRACT FROM AUTHOR]

A combinatorial study of the effect of in‐mixing of various guests on the thermoelectric properties of the host workhorse polymer poly[2,5‐bis(3‐tetradecylthiophen‐2‐yl)thieno[3,2‐b]thiophene] (PBTTT) is presented. Specifically, the composition and thickness for doped films of PBTTT blended with different polymers are varied. Some blends at guest weight fractions around 10–15% exhibit up to a fivefold increase in power factor compared to the reference material, leading to zT values around 0.1. Spectroscopic analysis of the charge‐transfer species, structural characterization using grazing‐incidence wide‐angle X‐ray scattering, differential scanning calorimetry, Raman, and atomic force microscopy, and Monte Carlo simulations are employed to determine that the key to improved performance is for the guest to promote long‐range electrical connectivity and low disorder, together with similar highest occupied molecular orbital levels for both materials in order to ensure electronic connectivity are combined. [ABSTRACT FROM AUTHOR]

A major attraction of organic conjugated semiconductors is that materials with new, emergent functionality can be designed and made by simple blending, as is extensively used in, e.g., bulk heterojunction organic solar cells. Herein doped blends based on organic semiconductors (OSCs) for thermoelectric applications are critically reviewed. Several experimental strategies to improve thermoelectric performance, measured in terms of power factor (PF) or figure‐of‐merit ZT, have been demonstrated in recent literature. Specifically, density‐of‐states design in blends of two OSCs can be used to obtain electronic Seebeck coefficients up to ≈2000 µV K−1. Alternatively, blending with (high‐dielectric constant) insulating polymers can improve doping efficiency and thereby conductivity, as well as induce more favorable morphologies that improve conductivity while hardly affecting thermopower. In the PEDOT:polystyrene‐sulfonate (PEDOT:PSS) blend system, processing schemes to either improve conductivity via morphology or via (partial) removal of the electronically isolating PSS, or both, have been demonstrated. Although a range of experiments have at least quasi‐quantitatively been explained by analytical or numerical models, a comprehensive model for organic thermoelectrics is lacking so far. [ABSTRACT FROM AUTHOR]