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 η d 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 η d , 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 η d and led to a rapid increase of the power factor with increasing σ: S 2 σ ∝ σ 0.76 . 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.