Spectral Engineering in π-Conjugated Polymers with Intramolecular Donor−Acceptor Interactions

Beaujuge, Pierre M.; Amb, Chad M.; Reynolds, John R.

doi:10.1021/ar100043u

Cited by 578 publications

(481 citation statements)

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“…In dilute solutions, as shown in Figure 1, PBDThDTBT and PBDTchDTBT exhibited almost unanimous intramolecular CT transition absorption 38 centered at ∼595 nm, indicating that although cyclohexyl could result in larger θ1, however, such …”

Section: −5mentioning

confidence: 98%

Intra- and Intermolecular Steric Hindrance Effects Induced Higher Open-Circuit Voltage and Power Conversion Efficiency

Han

Chen

et al. 2015

ACS Macro Lett.

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A pair of donor−acceptor polymers PBDThDTBT and PBDTchDTBT are synthesized, which share the same conjugated backbone, but are designed with hexyl and cyclohexyl side chains, respectively. The stronger steric hindrance of cyclohexyl endows PBDTchDTBT a deeper lying HOMO energy level of −5.39 eV compared to −5.22 eV for PBDThDTBT. However, PBDThDTBT and PBDTchDTBT exhibit a similar optical bandgap around 1.72 eV and a hole mobility around 10 −5 cm 2 V −1 s −1 . Interestingly, the PBDTchDTBT/PC 71 BM blends exhibited higher hole mobility than PBDThDTBT/PC 71 BM after DIO was added. The higher hole mobility and fibrillar network in the active layer endows PBDTchDTBT higher power conversion efficiency of 7.9%, together with simultaneously improved open-circuit voltage of 0.80 V, short-circuit current density of 13.50 mA cm, and fill factor of 72.74% after a systemic study of their solar cell devices. S emiconducting polymer is considered as the ideal material for next generation large area optoelectronics application in virtue of its superior solution processing and film forming ability.1−5 When a semiconducting polymer is employed, research is mainly focused on its frontier molecular orbital energy levels and optical and optoelectronic characteristics, which have reliance on the polymer's planarity, interchain aggregation, alkyl substituents, and molecular weight.6−9 One simple and effective strategy employed to adjust the energy levels and optical property of a semiconducting polymer is intra-or intermolecular steric hindrance effect (SHE). 10−13However, SHE has been reported with negative effect on molecular self-organization in the donor−acceptor (D−A) oligmers.14 Intermolecular SHE introduced to the polymer backbone could prevent molecular packing and then result in weaker crystallinity.15 Intramolecular SHE may reduce the π-orbital overlap between two adjacent units and lead to undesirable hypochromatic shifted absorption spectra and wide bandgap (E g ), 10,16−20 however, as is well-known, wide absorption spectra, and narrow E g of the absorber are crucial for organic solar cells (OSCs) application. 21Although SHE has been considered as a negative effect for polymer's self-aggregation and effective conjugation, one advantage should be pointed out, that is, SHE can significantly decrease the highest occupied molecular orbital (HOMO) energy levels of the polymer. For example, poly(3-cyclohexylthiophene) (P3chT) exhibited more twisted conjugating backbone than poly(3-hexylthiophene) (P3hT) because of stronger SHE of cyclohexyl than hexyl, which resulted in a larger dihedral angle (θ) between the two adjacent thiophene rings together with a wider E g and a deeper lying HOMO of −5.72 eV, 0.72 eV lower than that of P3hT (−5.0 eV) experimentally.10 Theoretically, Bredas and co-workers reported that the ionic potential of the polythiophene increased gradually as the torsion angle increased from 0 to 90°.22 This

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Section: −5mentioning

confidence: 98%

Intra- and Intermolecular Steric Hindrance Effects Induced Higher Open-Circuit Voltage and Power Conversion Efficiency

Han

Chen

et al. 2015

ACS Macro Lett.

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“…Secondly, inserting acceptor moieties as n-type units [i.e., diketopyrrolopyrrole (DPP), naphthalene-bis(dicarboximide) (NDI), etc.] into p-type moieties has become a very efficient strategy to synthesize more conjugated polymers by employing the intense intra-and inter-chain donor-acceptor interactions recently [11,86,[99][100][101][102][103]. Take DPP unit for an example, the combination of DPP and thiophene, that is, dithienyl-DPPs, show excellent planarity with a small torsion of only 12 degrees due to both the intense donor-acceptor interaction via electron transfer and the favorable intra-molecular S-O interaction [11].…”

Section: The Effect Of Planarity and Rigidity On Structure Morphologmentioning

confidence: 99%

Structure and Morphology Control in Thin Films of Conjugated Polymers for an Improved Charge Transport

Wang

et al. 2013

Polymers

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Abstract:The morphological and structural features of the conjugated polymer films play an important role in the charge transport and the final performance of organic optoelectronics devices [such as organic thin-film transistor (OTFT) and organic photovoltaic cell (OPV), etc.] in terms of crystallinity, packing of polymer chains and connection between crystal domains. This review will discuss how the conjugated polymer solidify into, for instance, thin-film structures, and how to control the molecular arrangement of such functional polymer architectures by controlling the polymer chain rigidity, polymer solution aggregation, suitable processing procedures, etc. These basic elements in intrinsic properties and processing strategy described here would be helpful to understand the correlation between morphology and charge transport properties and guide the preparation of efficient functional conjugated polymer films correspondingly.

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“…1(b), where the absorption at a shorter wavelength arises from the D unit and the absorption at a longer wavelength arises from the internal charge transfer between D and A units in the copolymer, as observed in other D/A-type copolymers with similar chemical structure. 3,4,38 The absence of vibronic absorption indicates a disordered nature of the polymer.…”

Section: Resultsmentioning

confidence: 99%

Charge transport in amorphous low bandgap conjugated polymer/fullerene films

Kim¹,

Cho²,

Noh³

et al. 2012

Journal of Applied Physics

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The structural and charge transport properties of a low bandgap copolymer poly(3-hexylthiophene-alt-6,7-dimethyl-4,9-bis-(4-hexylthien-2yl)-[1,2,5]thiadiazolo[3,4-g]quinoxaline) (P(3HT-MeTDQ)) and its blend with [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) are investigated. Thermal analysis, X-ray scattering diffraction (XRD), atomic force microscopy and transmission electron microscopy (TEM) of P(3HT-MeTDQ) reveal that the polymer is amorphous in solid state. As the hole mobility of P(3HT-MeTDQ) was measured by the time-of-flight photoconductivity method, the mobility was 3.35 × 10−4 cm2/V s, which is very comparable to that of semicrystalline poly(3-hexyl thiophene). When the mobility of amorphous P(3HT-MeTDQ) was analyzed according to the Gaussian disorder model, the polymer has the energetic and positional disorders with the values of σ = 62 meV and Σ = 1.7, respectively, indicating that the polymer has a relatively narrow Gaussian distribution of transport states. Interestingly, when P(3HT-MeTDQ) is blended with PCBM, the amorphous P(3HT-MeTDQ) becomes partially ordered, as evidenced by observation of two discernible XRD peaks at 2θ = 5° (d = 17.7 Å) and 25.5° (d = 3.5 Å) corresponding to the interchain distance and π-stacking distance, respectively. The bicontinuous network morphology was identified at the blend with 60 wt. % PCBM by TEM, at which the charge carrier transport changes from hole-only to ambipolar.

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Spectral Engineering in π-Conjugated Polymers with Intramolecular Donor−Acceptor Interactions

Cited by 578 publications

References 31 publications

Intra- and Intermolecular Steric Hindrance Effects Induced Higher Open-Circuit Voltage and Power Conversion Efficiency

Intra- and Intermolecular Steric Hindrance Effects Induced Higher Open-Circuit Voltage and Power Conversion Efficiency

Structure and Morphology Control in Thin Films of Conjugated Polymers for an Improved Charge Transport

Charge transport in amorphous low bandgap conjugated polymer/fullerene films

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