Various pure organic semiconducting molecules exhibit extraordinarily large Seebeck coefficient which cannot be elucidated by conventional physical models of thermoelectricity.

Carbon nanotubes (CNTs) are an attractive material for flexible thermoelectric devices because of their mechanical strength, lightness, and high conductivity. However, their thermoelectric performance is restricted by their large thermal conductivity. In this letter, a novel material design for improving the performance of CNTs by inserting biobased molecules at CNT/CNT junctions is proposed. We demonstrate that the thermal conductivity is markedly suppressed, but the electrical conductivity is increased by the addition of cage-shaped proteins with semiconducting cores. The Seebeck coefficient also increases by selecting the appropriate core material. By improving the three above-mentioned important parameters, the ZT value is increased over 1000-fold.

Layer-by-layer fabrication of uniformly oriented thin films over large areas by cost-effective solution-based approaches can open new horizons for the realization of high-performance organic circuits in various applications. In this work, fabrication of a large-area ≈40 cm 2 film with uniform orientation is reported for poly(3,3‴-dialkylquaterthiophene) (PQT) using a unidirectional floating film transfer method (UFTM). Orientation characteristics and charge transport anisotropy were analyzed using polarized UV−vis spectral mapping and fabrication of bottom-gated organic field-effect transistors (OFETs) from different regions. Films were found to be highly oriented with an optical dichroic ratio of ca. 15. Orientation characteristics reveal that films were highly oriented along the width of the film, covering >70% of the area, and angledependent field-effect mobilities are in good agreement with the orientation of the polymer backbones. These highly oriented films resulted in charge transport anisotropy of 8.9. An array of bottom-gated OFETs fabricated along the length of single large-area (≈15 × 2.5 cm 2 ) thin film demonstrated the average field-effect mobility of 0.0262 cm 2 /(V s) with a very narrow standard deviation of 12.6%. We also demonstrated that film thickness can be easily tuned from 5.6 to 45 nm by increasing the PQT concentration, and field-effect mobility is highly reproducible even when the film thickness is 10 nm. Microstructural characterization of the thusprepared large-area thin films revealed the edge-on stacked polymer backbones and surface roughness of <1 nm as probed by grazing incidence X-ray diffraction and atomic force microscopy, respectively. Flexible OFETs with bottom-gate top-contact geometry were also fabricated, having average field-effect mobility of 0.0181 cm 2 /(V s). There was no considerable change in mobility after bending the flexible devices at different radii.

The small thermal conductivity of molecular solids is beneficial for their thermoelectric applications. If Seebeck coefficients were sufficiently large to compensate for the relatively small electrical conductivity, these materials would be promising candidates for thermoelectric devices. In this work, the thermoelectric properties of C60 were studied by in situ measurements under ultrahigh vacuum after the deposition of a pure C60 thin film. An exceptionally large Seebeck coefficient of more than 150 mV/K was observed as a steady-state thermoelectromotive force. Even considering several extreme but realistic conditions, conventional semiclassical thermoelectric theories cannot explain this giant Seebeck effect.

In addition, their chemical tunability, and potential for coating large areas make these materials attractive for roll-to-roll processing. [2,3] Further, the charge transport in SCPs is highly anisotropic because of the presence of three possible directions with different magnitudes of orbital overlap, which decrease in the following order: along the π-conjugated main chain, along the π−stacking direction, and through the insulating side chains. As a result, control over the alignment of SCPs in films can significantly modulate their electronic properties. [4] Further, the controlled orientation of SCPs is beneficial for improving charge transport and understanding their anisotropic properties to optimize the chemical structure. In particular, the uniaxial alignment of SCPs parallel to the channel direction of organic field-effect transistors (OFET) promotes in-plane charge transport, resulting in a high fieldeffect mobility (µ), [4] and several excellent reviews concerning alignment methods for SCPs for application in OFETs have been published. [4][5][6][7] Recently, there has been considerable interest in fabricating active-layer films on liquid substrates (both of SCPs and small molecules) that can, thus, be transferred to arbitrary substrates. [8][9][10] Importantly, compared to conventional solution processing methods, this strategy offers better control of the film morphology because of the use of a liquid substrate; specifically, in conventional methods, the morphology of the resultant film is strongly affected by the interfacial properties of the device substrate. In contrast, when using a liquid substrate, the films are transferred to the device substrate after solvent evaporation, and the morphology of any underlying film is unaffected, thus facilitating the development of layer-by-layer structures without the need for orthogonal solvents. [11][12][13] Morita et al. [14] first reported the floating film transfer method (FTM), and they demonstrated that the preparation of thin floating films of poly(3-hexylthiophene) on a hydrophilic liquid substrate resulted in better optoelectronic properties than those prepared by spin-coating method. Subsequently, FTM has been applied for the preparation of various SCPs. [8,12,13,[15][16][17][18][19] The orientational control of semiconducting polymers (SCPs) in floating films offers several advantages over conventional solution-processing methods for device fabrication, and the unidirectional floating film transfer method (UFTM) has been applied to fabricate large-area oriented p-type SCP films. Here, UFTM can be used to prepare high-performance n-type SCP films of P(NDI2OD-T2) is reported. A strong correlation between the degree of polymer orientation and the solvent used for the preparation of P(NDI2OD-T2) floating films is observed. In particular, the size of the nanofibers aligned along the orientation direction prepared using chloroform is dramatically increased by adding a small amount of chlorobenzene. Microstructural characterization reveals that the P(NDI2O...