How intermolecular geometrical disorder affects the molecular doping of donor–acceptor copolymers

• Published in: Nature communications 2015-03, Vol.6 (1), p.6460-6460, Article 6460
• Main Authors: Di Nuzzo, Daniele, Fontanesi, Claudio, Jones, Rebecca, Allard, Sybille, Dumsch, Ines, Scherf, Ullrich, von Hauff, Elizabeth, Schumacher, Stefan, Da Como, Enrico
• Format: Article
• Language: English
• Subjects: 119/118; 639/301/119/1000; 639/301/923/1028; 639/638/440/947; Humanities and Social Sciences; multidisciplinary; Science; Science (multidisciplinary)
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/ncomms7460

Molecular doping of conjugated polymers represents an important strategy for improving organic electronic devices. However, the widely reported low efficiency of doping remains a crucial limitation to obtain high performance. Here we investigate how charge transfer between dopant and donor–acceptor copolymers is affected by the spatial arrangement of the dopant molecule with respect to the copolymer repeat unit. We p-dope a donor–acceptor copolymer and probe its charge-sensitive molecular vibrations in films by infrared spectroscopy. We find that, compared with a related homopolymer, a four times higher dopant/polymer molar ratio is needed to observe signatures of charges. By DFT methods, we simulate the vibrational spectra, moving the dopant along the copolymer backbone and finding that efficient charge transfer occurs only when the dopant is close to the donor moiety. Our results show that the donor–acceptor structure poses an obstacle to efficient doping, with the acceptor moiety being inactive for p-type doping. Doping of conjugated polymers is an important strategy for the development of organic electronics. Here, the authors study the spatial organization of dopants in donor–acceptor polymers, indicating that charge transfer is improved when the dopant and donor moiety are in close proximity.