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Nature of Charge Carriers in a High Electron Mobility Naphthalenediimide Based Semiconducting Copolymer
Author(s) -
D'Innocenzo Valerio,
Luzio Alessandro,
Petrozza Annamaria,
Fazzi Daniele,
Caironi Mario
Publication year - 2014
Publication title -
advanced functional materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 6.069
H-Index - 322
eISSN - 1616-3028
pISSN - 1616-301X
DOI - 10.1002/adfm.201400394
Subject(s) - materials science , polaron , electron mobility , charge carrier , density functional theory , acceptor , chemical physics , copolymer , electron , annealing (glass) , polymer , condensed matter physics , optoelectronics , computational chemistry , chemistry , physics , quantum mechanics , composite material
The nature of charge carriers in recently developed high mobility semiconducting donor‐acceptor polymers is debated. Here, localization due to charge relaxation is investigated in a prototypal system, a good electron transporting naphthalenediimide based copolymer, by means of current‐voltage I ‐ V electrical characteristics and charge modulation spectroscopy (CMS) in top‐gate field‐effect transistors (FETs), combined with density functional theory (DFT) and time dependent DFT (TDDFT) calculations. In particular, pristine copolymer films are compared with films that underwent a melt‐annealing process, the latter leading to a drastic change of the microstructure. Despite the packing modification, which involves also the channel region, both the electron mobility and the energy of polaronic transitions are substantially unchanged upon melt‐annealing. The polaron absorption features can be rationalized and reproduced by TDDFT calculations for isolated charged oligomers. Therefore, it is concluded that in such a high electron mobility copolymer the charge transport process involves polaronic species which are intramolecular in nature and, from a more general point of view, that interchain delocalization of the polaron is not necessary to sustain charge mobilities in the 0.1 to 1 cm 2 V – 1 s –1 range. These findings contribute to the rationalization of the charge transport process in the recently developed class of donor‐acceptor π‐conjugated copolymers featuring high charge mobilities and complex morphologies.