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Understanding doping mechanisms is essential for optimizing the doping efficiency and rationally designing next generations of dopants and organic materials. Over the last few years, N-DMBI became a reference solution-processed n-type dopant, affording decent air-stability and record power factor for thermoelectric energy generation. Nevertheless, a complete description of doping mechanism including the activation conditions, the doping pathways, and possible side reactions is still lacking. In this work, we combined experimental and theoretical evidence to clarify the activation conditions of N-DMBI and elucidate the prevalent doping pathway depending on the dielectric constant of the medium. In polar media, direct doping via hydride H− transfer is largely dominant, while, in apolar media, singly occupied molecular orbital-mediated doping after H• release is thermodynamically favored. We show that N-DMBI can be activated not only by thermal annealing above 100 °C, but also by UV-light irradiation at low fluences even in thin films. Our findings stress the importance of working in strictly anoxic environment to avoid parasitic O2-mediated side reactions, even in the presence of a host. [ABSTRACT FROM AUTHOR]

The impact of the chemical structure and molecular order on the charge transport properties of two donor–acceptor copolymers in their neutral and doped states is investigated. Both polymers comprise 3,7‐bis((E)‐7‐fluoro‐1‐(2‐octyl‐dodecyl)‐2‐oxoindolin‐3‐ylidene)‐3,7‐dihydrobenzo[1,2‐b:4,5‐b′]difuran‐2,6‐dione (FBDOPV) as electron‐accepting unit, copolymerized with 9,9‐dioctyl‐fluorene (P(FBDOPV‐F)) or with 3‐dodecyl‐2,2′‐bithiophene (P(FBDOPV‐2T‐C12)). These copolymers possess an amorphous and semi‐crystalline nature, respectively, and exhibit remarkable electron mobilities of 0.065 and 0.25 cm2 V–1 s–1 in field effect transistors. However, after chemical n‐doping with 4‐(1,3‐dimethyl‐2,3‐dihydro‐1H‐benzoimidazol‐2‐yl)phenyl)dimethylamine (N‐DMBI), electrical conductivities four orders of magnitude higher can be achieved for P(FBDOPV‐2T‐C12) (σ = 0.042 S cm−1). More charge‐transfer complexes are formed between P(FBDOPV‐F) and N‐DMBI, but the highly localized polaronic states poorly contribute to the charge transport. Doped P(FBDOPV‐2T‐C12) exhibits a negative Seebeck coefficient of –265 µV K−1 and a thermoelectric power factor (PF) of 0.30 µW m−1 K−2 at 303 K which increases to 0.72 µW m−1 K−2 at 388 K. The in‐plane thermal conductivity (κ|| = 0.53 W m−1 K−1) on the same micrometer‐thick solution‐processed film is measured, resulting in a figure of merit (ZT) of 5.0 × 10−4 at 388 K. The results provide important design guidelines to improve the doping efficiency and thermoelectric properties of n‐type organic semiconductors. [ABSTRACT FROM AUTHOR]