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Driving Force and Optical Signatures of Bipolaron Formation in Chemically Doped Conjugated Polymers
Author(s) -
Voss Matthew G.,
Challa J. Reddy,
Scholes D. Tyler,
Yee Patrick Y.,
Wu Eric C.,
Liu Xiao,
Park Sanghyun J.,
León Ruiz Omar,
Subramaniyan Selvam,
Chen Mengdan,
Jenekhe Samson A.,
Wang Xiaolin,
Tolbert Sarah H.,
Schwartz Benjamin J.
Publication year - 2021
Publication title -
advanced materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 10.707
H-Index - 527
eISSN - 1521-4095
pISSN - 0935-9648
DOI - 10.1002/adma.202000228
Subject(s) - bipolaron , polaron , materials science , dopant , doping , conjugated system , charge carrier , chemical physics , conductive polymer , polymer , spectroscopy , ultrafast laser spectroscopy , optoelectronics , conductivity , chemistry , electron , physics , composite material , quantum mechanics
Molecular dopants are often added to semiconducting polymers to improve electrical conductivity. However, the use of such dopants does not always produce mobile charge carriers. In this work, ultrafast spectroscopy is used to explore the nature of the carriers created following doping of conjugated push–pull polymers with both F 4 TCNQ (2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane) and FeCl 3 . It is shown that for one particular push–pull material, the charge carriers created by doping are entirely non‐conductive bipolarons and not single polarons, and that transient absorption spectroscopy following excitation in the infrared can readily distinguish the two types of charge carriers. Based on density functional theory calculations and experiments on multiple push–pull conjugated polymers, it is argued that the size of the donor push units determines the relative stabilities of polarons and bipolarons, with larger donor units stabilizing the bipolarons by providing more area for two charges to co‐reside.