Position‐Induced Efficient Doping for Highly Doped Organic Thermoelectric Materials

Abstract

Electrical doping is essentially required for high‐performance organic thermoelectric (TE) materials; however, the doping efficiency ηd has not been extensively investigated in highly doped organic semiconductors (OSCs). Here, it is demonstrated that the distribution of dopant molecules in a specific position in highly doped OSCs affects the ηd, which is critically related to the Seebeck coefficient S and the electrical conductivity σ. Poly(2,5‐bis(3‐hexadecylthiophen‐2‐yl)thieno[3,2‐b]thiophene) (PBTTT) films are p‐doped with 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane (F4TCNQ) by either solution‐sequential (SSq) doping or vapor doping. SSq doping deposited F4TCNQ only in the amorphous domains of PBTTT films, whereas vapor doping deposited it in both the amorphous and crystalline domains. F4TCNQ molecules in the crystalline domains exhibited a high ηd and led to a rapid increase of the power factor with increasing σ: S2σ ∝ σ0.76. These results provide guidance for the efficient doping of highly doped OSCs and emphasize the importance of doping efficiency in obtaining high‐performance organic TE materials.

Extremely Suppressed Energetic Disorder in a Chemically Doped Conjugated Polymer

“…The estimated polaron size of IDTBT (6.7 nm) was larger than that reported for PBTTT (<4.8 nm) with high crystallinity, indicating that the doped IDTBT could exhibit excellent electrical properties. [23,24] Although undoped monomers occupied a significant proportion of the total number of monomers at [OA] = 0.4, a polaron was delocalized across 4.2 monomers and they could be close to each other and condensed to form a bipolaron. In the UV/Vis/NIR spectra, the neutral peaks were completely bleached at [OA] = 0.8, leaving a continuous absorption band within the bandgap; this result is further evidence of the coexistence of polaron bands and bipolaron bands within the intrinsic bandgap (Figure 1d and Figure S13, Supporting Information).…”

Optimizing chain alignment and preserving the pristine structure of single-ether based PBTTT helps improve thermoelectric properties in sequentially doped thin films

“…For most PSCs, the processing conditions (temperature, solvent, film preparation method) determine the dominant contact planes of the crystals on a substrate. [26][27][28][29][30] For P3HT and PBTTT, different crystal orientations on a substrate are observed depending on the type of solvent used, the temperature of an annealing step or the molecular weight of the polymer. In this work, we have studied the way the growth conditions (rubbing temperature T R ) of oriented PSC thin films affect the resulting anisotropic TE properties in the doped thin films.…”

Novel Dithienopyrrole‐Based Conjugated Copolymers: Importance of Backbone Planarity in Achieving High Electrical Conductivity and Thermoelectric Performance

“…[37] In addition, different doping efficiencies and morphological changes of different material systems upon doping further complicates the comparison of the Seebeck coefficients between material systems. [38,39] Despite the complexity, we tried to interpret the relationship between the Seebeck coefficient and electrical conductivity for the doped polymers, using the charge transport model for conducting polymers (Figure S13b, Supporting Information). In this model, the electrical conductivity is expressed by the following equations [37] 1)…”