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. 2021 Apr 28;7(18):eabe5280.
doi: 10.1126/sciadv.abe5280. Print 2021 Apr.

Charge transport physics of a unique class of rigid-rod conjugated polymers with fused-ring conjugated units linked by double carbon-carbon bonds

Mingfei Xiao  1 , Remington L Carey  1 , Hu Chen  2 , Xuechen Jiao  3   4 , Vincent Lemaur  5 , Sam Schott  1 , Mark Nikolka  1 , Cameron Jellett  6 , Aditya Sadhanala  1   7 , Sarah Rogers  8 , Satyaprasad P Senanayak  1   9 , Ada Onwubiko  6 , Sanyang Han  1 , Zhilong Zhang  1 , Mojtaba Abdi-Jalebi  1   10 , Youcheng Zhang  1 , Tudor H Thomas  1 , Najet Mahmoudi  8 , Lianglun Lai  1   11 , Ekaterina Selezneva  1 , Xinglong Ren  1 , Malgorzata Nguyen  1 , Qijing Wang  1 , Ian Jacobs  1 , Wan Yue  12 , Christopher R McNeill  3 , Guoming Liu  1   13   14 , David Beljonne  5 , Iain McCulloch  2   6 , Henning Sirringhaus  15
Affiliations

Charge transport physics of a unique class of rigid-rod conjugated polymers with fused-ring conjugated units linked by double carbon-carbon bonds

Mingfei Xiao et al. Sci Adv. .

Abstract

We investigate the charge transport physics of a previously unidentified class of electron-deficient conjugated polymers that do not contain any single bonds linking monomer units along the backbone but only double-bond linkages. Such polymers would be expected to behave as rigid rods, but little is known about their actual chain conformations and electronic structure. Here, we present a detailed study of the structural and charge transport properties of a family of four such polymers. By adopting a copolymer design, we achieve high electron mobilities up to 0.5 cm2 V-1 s-1 Field-induced electron spin resonance measurements of charge dynamics provide evidence for relatively slow hopping over, however, long distances. Our work provides important insights into the factors that limit charge transport in this unique class of polymers and allows us to identify molecular design strategies for achieving even higher levels of performance.

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Figures

Fig. 1
Fig. 1. Chemical structures and thin-film UV-Vis-NIR absorption spectra.
(A) Chemical structure of NN1, NN2, AN1, AN2, and P(NDI2OD-T2) polymers. (B) Thin-film UV-Vis-NIR absorption spectra of the polymers. The films were spun from hot 1,2,4-trichlorobenzene solution.
Fig. 2
Fig. 2. SANS of NN1, NN2, AN2, and P(NDI2OD-T2) in hot, dichlorobenzene solution.
The NN1, NN2, and AN2 fused polymers adopt a rigid-rod shape with a scaling of I ≈ q−1 over a large region, while the semiflexible P(NDI2OD-T2) polymer shows a characteristic worm-like chain behavior. The curves have been shifted vertically for clarity. The incoherent scattering background was subtracted.
Fig. 3
Fig. 3. Structural characterization of the representative rigid-rod polymer thin films.
(A) 2D GIWAXS patterns of NN1, NN2, and AN2 thin-film samples. (B) In-plane and out-of-plane 1D linecuts of NN1, NN2, and AN2’s 2D GIWAXS patterns.
Fig. 4
Fig. 4. PDS of rigid-rod polymer thin films.
Absorbance of the NN1, NN2, AN1, and AN2 thin films measured by PDS. Dotted lines represent exponential tail fits for extraction of the Urbach energies Eu (inset).
Fig. 5
Fig. 5. Temperature-dependent and molecular weight–dependent charge transport investigation of rigid-rod polymer FETs.
(A) Transfer curves measured on top-gate, bottom-contact FETs (L = 20 μm, W = 1 mm) fabricated from the spin-coated AN2 film. (B) Linear and saturation mobility extracted from transfer curves measured on the same device. (C) Molecular weight–dependent saturation mobility for spin-coated NN1, NN2, AN1, and AN2 top-gate, bottom-contact FETs (L = 20 μm, W = 1 mm). (D) Temperature-dependent saturation electron mobility (at VG = 60 V, VD = 60 V) for spin-coated NN1, NN2, AN1, and AN2 top-gate, bottom-contact FETs (L = 20 μm, W = 1 mm).
Fig. 6
Fig. 6. Environmental and stress stability investigation of rigid-rod polymer FETs.
(A) Saturation electron mobility of NN1, NN2, AN1, AN2, and P(NDI2OD-T2) top-gate, bottom-contact OFETs (L = 20 μm, W = 1 mm) measured under various air exposure time, highlighting the air stability of electron transport of fused polymer OFETs in comparison to the P(NDI2OD-T2) OFET. (B) Saturation transfer curves (with p- and n-channel accumulation) for a representative AN2 OFET measured in the air after 450-hour continuous air exposure to demonstrate the operational stability of the sufficiently air-exposed device.
Fig. 7
Fig. 7. FI-ESR characterization of rigid-rod polymers.
FI-ESR spectra of the top-gate, bottom-contact sample (L = 100 μm, W = 243 mm) fabricated from spin-coated (A) NN1 and (D) AN2 film at 5 and 170 K. Spin lifetimes T1 and T2 for electron polarons in (B) NN1 and (E) AN2 FI-ESR sample at VG = 60 V. Motion frequency of charges determined from T2 (left axis) and saturation mobilities from FET measurements at VG = 60 V (right axis) of (C) NN1 and (F) AN2 FI-ESR samples. Labels show the calculated hopping distances in the motional narrowing regime by relating the motion frequency and saturation electron mobility with the Einstein relation for charge transport.
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