Cyano substituted benzothiadiazole: a novel acceptor inducing n-type behaviour in conjugated polymers

Casey, Abby; Han, Yang; Fei, Zhuping; White, Andrew J. P.; Anthopoulos, Thomas D.; Heeney, Martin

doi:10.1039/c4tc02008a

Cited by 92 publications

(108 citation statements)

References 53 publications

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“…Scheme 1. Synthetic procedures for a) monomer bis-Br(DTCNBT) b) monomer bis-Br(DTDCNBT) 34 and c) polymers P(Ge-DTBT) 26 , P(Ge-DTCNBT), P(Ge-DTDCNBT). 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 Table 1: Molecular weights and optical properties of P(Ge-DTBT), P(Ge-DTCNBT) and P(Ge-DTDCNBT) a Molecular weights measured using gel permeation chromatography (against polystyrene standards) in chlorobenzene at 80°C.…”

Section: Synthesis Of Monomers and Polymersmentioning

confidence: 99%

Effect of Systematically Tuning Conjugated Donor Polymer Lowest Unoccupied Molecular Orbital Levels via Cyano Substitution on Organic Photovoltaic Device Performance

et al. 2016

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We report a systematic study into the effects of cyano substitution on the electron accepting ability of the common acceptor 4,7-bis(thiophen-2-yl)-2,1,3-benzothiadiazole (DTBT). We describe the synthesis of DTBT monomers with either zero, 1 or 2 cyano groups on the BT unit, and their corresponding co-polymers with the electron rich donor dithienogermole (DTG). The presence of the cyano group is found to have a strong influence on the optoelectronic properties of the resulting donor-acceptor polymers, with the optical band gap red-shifting by approximately 0.15 eV per cyano substituent. We find that the polymer electron affinity is significantly increased by ca. 0.25 eV upon addition of each cyano group, whilst the ionization potential is less strongly affected, increasing by less than 0.1 eV per cyano substituent. In organic photovoltaic (OPV) devices power conversion efficiencies (PCE) are almost doubled from around 3.5% for the unsubstituted BT polymer to over 6.5% for the mono-cyano substituted BT polymer However, the PCE drops to less than 1% for the di-cyano substituted BT polymer. These differences are mainly related to differences in the photocurrent, which varies by one order of magnitude between the best (1CN) and worst devices (2CN). The origin of this variation in photocurrent was investigated by studying the charge generation properties of the photoactive polymer:fullerene blends using fluorescence and transient absorption spectroscopic techniques. These measurements revealed that the improved photocurrent of 1CN in comparison to 0CN was due to improved light harvesting properties whilst maintaining a high exciton dissociation yield. The addition of one cyano group to the BT unit optimized the position of the polymer LUMO level closer to that of the electron acceptor PC71BM, such that the polymer's light harvesting properties were improved without sacrificing either exciton dissociation yield or device V OC . We also identify that the drop in performance for the 2CN polymer is caused by very limited yields of electron transfer from the polymer to the fullerene LUMO levels, likely caused by poor orbital energy level alignment with the fullerene acceptor (PC71BM). This work highlights the impact that small changes in chemical structure can have on the optoelectronic and device properties of semiconducting polymer. In particular this work highlights the effect of LUMO-LUMO offset on the excited state dynamics of polymer:fullerene blends.

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Section: Synthesis Of Monomers and Polymersmentioning

confidence: 99%

Effect of Systematically Tuning Conjugated Donor Polymer Lowest Unoccupied Molecular Orbital Levels via Cyano Substitution on Organic Photovoltaic Device Performance

et al. 2016

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“…63,69,[85][86][87][88][89][90] The previously mentioned polymer 21 originally synthesized by Heeney and coworkers was also examined as a component of TFTs with a promising mobility of 0.11 cm 2 V -1 s -1 noted. 87 Similarly, the previously described dithienogermole and germafluorene copolymers 54-60 ( Fig.…”

Section: Transistors and Semi-conducting Materialsmentioning

confidence: 99%

Marriage of heavy main group elements with π-conjugated materials for optoelectronic applications

2016

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This review article summarizes recent progress in the synthesis and optoelectronic properties of conjugated materials containing heavy main group elements from Group 13-16 as integral components. As will be discussed, the introduction of these elements can promote novel phosphorescent behavior and support desirable molecular and polymeric properties such as low optical band gaps and high charge mobilities for photovoltaic and thin film transistor applications.

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“…[13][14][15][16] For example, we have previously shown that replacing dithienyl benzothiadiazole (DTBT) with dithienylthiadiazolopyridine (DTPyT) could lead to a lowered LUMO level (by ~ 0.3 eV) and a narrowed band gap (by ~ 0.2 eV) when each was copolymerized with BnDT. 13 Inspired by this successful precedent and others, [14][15][16] we envisioned a general modification strategy for the parent benzotriazole (TAZ) (Chart 1), aiming to enhance the electron withdrawing nature of the moiety 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 5 m-TAZ while preserving its other beneficial structural features. However, building such a library of triazole acceptors would be very challenging if one chose to painstakingly synthesize each proposed structural modification of m-TAZ from individual starting materials, though we and others have taken such individualized syntheses for other structurally related acceptors (Scheme S1).…”

Section: Chart 1 General Structure Of Triazole Based Acceptorsmentioning

confidence: 99%

A General Approach toward Electron Deficient Triazole Units to Construct Conjugated Polymers for Solar Cells

Yan

Zhou

et al. 2015

Chem. Mater.

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Triazole based structural units have been widely used to construct conjugated polymers for optoelectronic applications; yet the design and synthesis of such units have been limited to just a few known examples. We report a general yet versatile synthetic approach towards a diverse set of triazole based conjugated molecules bearing various electron accepting abilities. The structural differences of as-synthesized three new triazole acceptors have a significant impact on the optoelectronic properties of conjugated polymers incorporating these triazoles. Bulk heterojunction solar cells based on one of these new polymers, PyCNTAZ, feature a high open circuit voltage of ~1 V and a notable efficiency of 8.4% with an active layer thickness around 300 nm.

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Cyano substituted benzothiadiazole: a novel acceptor inducing n-type behaviour in conjugated polymers

Abstract: The displacement of fluoride by cyanide offers a simple route to strongly electron accepting cyano substituted benzothiadiazole monomers. Copolymerisation with electron rich donors leads to low band gap polymers which exhibit electron transporting behaviour.

Cited by 92 publications

References 53 publications

Effect of Systematically Tuning Conjugated Donor Polymer Lowest Unoccupied Molecular Orbital Levels via Cyano Substitution on Organic Photovoltaic Device Performance

Effect of Systematically Tuning Conjugated Donor Polymer Lowest Unoccupied Molecular Orbital Levels via Cyano Substitution on Organic Photovoltaic Device Performance

Marriage of heavy main group elements with π-conjugated materials for optoelectronic applications

A General Approach toward Electron Deficient Triazole Units to Construct Conjugated Polymers for Solar Cells

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