n‐Dopants Based on Dimers of Benzimidazoline Radicals: Structures and Mechanism of Redox Reactions

Zhang, Siyuan; Naab, Benjamin D.; Jucov, Evgheni V.; Parkin, Sean; Evans, Eric G. B.; Millhauser, Glenn L.; Timofeeva, Tatiana V.; Risko, Chad; Brédas, Jean‐Luc; Bao, Zhenan; Barlow, Stephen; Marder, Seth R.

doi:10.1002/chem.201500611

Cited by 39 publications

(77 citation statements)

References 44 publications

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“…Furthermore, redox-active organic compounds were recently suggested for sustainable battery systems 7 , 8 . Although commercially employed in OLED displays, the working principle of molecular doping is still a controversial topic 9 – 12 , hindering the development of novel redox couples 13 , 14 . As initial step, either host-dopant electronic wave-function hybridization or ground-state integer-charge transfer (ICT) from donor (D) to acceptor (A) molecules were identified as fundamental mechanisms 15 , 16 .…”

Section: Introductionmentioning

confidence: 99%

Elementary steps in electrical doping of organic semiconductors

et al. 2018

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Fermi level control by doping is established since decades in inorganic semiconductors and has been successfully introduced in organic semiconductors. Despite its commercial success in the multi-billion OLED display business, molecular doping is little understood, with its elementary steps controversially discussed and mostly-empirical-materials design. Particularly puzzling is the efficient carrier release, despite a presumably large Coulomb barrier. Here we quantitatively investigate doping as a two-step process, involving single-electron transfer from donor to acceptor molecules and subsequent dissociation of the ground-state integer-charge transfer complex (ICTC). We show that carrier release by ICTC dissociation has an activation energy of only a few tens of meV, despite a Coulomb binding of several 100 meV. We resolve this discrepancy by taking energetic disorder into account. The overall doping process is explained by an extended semiconductor model in which occupation of ICTCs causes the classically known reserve regime at device-relevant doping concentrations.

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Section: Introductionmentioning

confidence: 99%

Elementary steps in electrical doping of organic semiconductors

et al. 2018

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“…[ 34 ] It is necessary to discuss the effective redox potential of (2-Cyc-DMBI) 2 to demonstrate that at equilibrium no unreacted dopant remains in the solution UV-Vis doping experiments. For a dimer doping reaction, doping will be endergonic when…”

Section: Doping Reaction Thermodynamicsmentioning

confidence: 99%

“…Consistent with this estimation, the previous study demonstrated that TIPS-pentacene ( E 0/− solution = −1.5 V vs Fc / Fc + ) was reduced by (2-Cyc-DMBI) 2 in solution. [ 34 ] TIPS-pentacene has a much higher LUMO energy than the polymers presented in Table 1 and, therefore, it is reasonable to assume that at low doping concentrations the reaction between (2-Cyc-DMBI) 2 and the PDI and NDI polymers is quantitative if the reaction is observed to reach equilibrium.…”

Section: Doping Reaction Thermodynamicsmentioning

confidence: 99%

Role of Polymer Structure on the Conductivity of N‐Doped Polymers

Naab

Kurosawa

et al. 2016

Adv Elect Materials

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113

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The n‐doping of several conjugated co‐polymers based on perylene diimide (PDI) and napthalene diimide (NDI) acceptors co‐polymerized with ethynylene, ethylene, and bithiophene by the dimeric dopant (2‐Cyc‐DMBI)2 is reported. The n‐doping reactions are confirmed in solution by UV–Vis–NIR spectroscopy and in thin films with photothermal deflection spectroscopy (PDS). The reduced species of the ethynylene‐linked polymers are found to be more delocalized along the polymer backbone than the bithiophene‐linked polymers by comparison of the absorption spectra. A high conductivity of 0.45 S cm−1 is measured for the ethynylene‐linked polymer P(PDI2OD‐A). In contrast, neither of the two bithiophene‐linked polymers, P(NDI2OD‐T2) and P(PDI2OD‐T2), achieve conductivities greater than 4 × 10−3 S cm−1. Furthermore, there is no correlation between the conductivity of the doped films and the mobility of the pure films used in this study. Grazing incidence X‐ray diffraction (GIXD) measurements of the films find that a similar doped phase forms irrespective of the crystallinity of the pure host polymer. In absence of a significant difference in morphology, these results suggest a link between the polaron delocalization length of the polymers and the conductivity, and more fundamentally between the backbone structure of the polymer and the polaron delocalization length.

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“…In these approaches, the actual n-dopant is either preserved within a precursor molecule, [11][12][13][14][15] or present as the corresponding dimer with suffi cient low energy levels to resist oxidation. [16][17][18][19][20] In all of these cases, n-type doping of fullerene fi lms, i.e., [6,6]-phenyl-C 61 -butyric acid methyl ester (PC 61 BM) or C 60 (electron affi nity EA = 4.0 eV), was demonstrated. [ 12,14,19 ] Moreover, successful n-doping of copper-phthalocyanine (CuPc, EA = 3.5 eV) with dimeric forms of rhodocene was reported.…”

Section: Introductionmentioning

confidence: 99%

Passivation of Molecular n‐Doping: Exploring the Limits of Air Stability

Tietze

Rose

Schwarze

et al. 2016

Adv Funct Materials

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Molecular doping is a key technique for fl exible and low-cost organic complementary semiconductor technologies that requires both effi cient and stable p-and n-type doping. However, in contrast to molecular p-dopants, highly effi cient n-type dopants are commonly sensitive to rapid degradation in air due to their low ionization energies ( IE s) required for electron donation, e.g., IE = 2.4 eV for tetrakis(1,3,4,6,7,8-hexahydro-2H -pyrimido[1,2-a ]pyrimidinato) ditungsten(II) (W 2 (hpp) 4 ). Here, the air stability of various host:W 2 (hpp) 4 combinations is compared by conductivity measurements and photoemission spectroscopy. A partial passivation of the n-doping against degradation is found, with this effect identifi ed to depend on the specifi c energy levels of the host material. Since host-W 2 (hpp) 4 electronic wavefunction hybridization is unlikely due to confi nement of the dopant highest occupied molecular orbital (HOMO) to its molecular center, this fi nding is explained via stabilization of the dopant by single-electron transfer to a host material whose energy levels are suffi ciently low for avoiding further charge transfer to oxygen-water complexes. Our results show the feasibility of temporarily handling n-doped organic thin fi lms in air, e.g., during structuring of organic fi eld effect transistors (OFETs) by lithography.

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n‐Dopants Based on Dimers of Benzimidazoline Radicals: Structures and Mechanism of Redox Reactions

Cited by 39 publications

References 44 publications

Elementary steps in electrical doping of organic semiconductors

Elementary steps in electrical doping of organic semiconductors

Role of Polymer Structure on the Conductivity of N‐Doped Polymers

Passivation of Molecular n‐Doping: Exploring the Limits of Air Stability

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