Fluorination increases the electron mobility of zinc azadipyrromethene-based electron acceptors and enhances the performance of fullerene-free organic solar cells

Pejić, Sandra; Thomsen, Anna M; Etheridge, Forrest S.; Fernando, Roshan; Wang, Chunlai; Sauvé, Geneviève

doi:10.1039/c7tc05820a

Cited by 12 publications

(21 citation statements)

References 42 publications

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“…The zinc chelate of L1 was synthesized by reacting with sodium hydride and zinc chloride to give a blue solid 75 % yield. [6b] Zn(L1) 2 was purified by column chromatography, and its identity and purity were confirmed by MALDI‐TOF MS, 1 H NMR, 13 C NMR, 19 F NMR, and elemental analysis.…”

Section: Resultsmentioning

confidence: 99%

“…To lower the energy levels of Zn(WS3) 2 , we explored fluorination at various positions on the ADP ligand: at the p ‐distal phenyl, p ‐proximal phenyl and p ‐pyrrolic phenylethynyls, A – D in Figure . Interestingly, we found that fluorination had very little effect on the redox properties and corresponding estimated HOMO/LUMO energy levels.…”

Section: Introductionmentioning

confidence: 99%

“…Amin et al also found that attaching fluorine to the p ‐distal phenyls of ADP, E in Figure , did not lower the energy levels of the BF 2 + chelate . On the other hand, addition of –F at the proximal phenyls ( C ) or –CF 3 at the pyrrolic phenylethynyls ( D ) of Zn(WS3) 2 decreased of the energy levels by 0.09–0.10 eV . When tested in organic solar cells with P3HT as the electron donor, all fluorinated compounds except for C (with p ‐proximal phenyl‐F) performed better than Zn(WS3) 2 ,[6a] showing that fluorination was nevertheless beneficial for OPV applications.…”

Section: Introductionmentioning

confidence: 99%

“…On the other hand, addition of –F at the proximal phenyls ( C ) or –CF 3 at the pyrrolic phenylethynyls ( D ) of Zn(WS3) 2 decreased of the energy levels by 0.09–0.10 eV . When tested in organic solar cells with P3HT as the electron donor, all fluorinated compounds except for C (with p ‐proximal phenyl‐F) performed better than Zn(WS3) 2 ,[6a] showing that fluorination was nevertheless beneficial for OPV applications. Additionally, fluorination was found to be beneficial for increasing electron mobility.…”

Section: Introductionmentioning

confidence: 99%

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Synthesis and Properties of Azadipyrromethene‐Based Complexes with Nitrile Substitution

et al. 2020

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Azadipyrromethene (ADP)‐based complexes have gained interest due to their strong absorption in the visible to near‐IR region and high electron affinity. Attempts to increase their electron accepting properties by electron withdrawing group substitutions have been limited. We previously found that substitution with fluorine at the p‐distal phenyls or at the p‐pyrrolic‐phenylethynyls of ADP do not shift reduction potentials and thus have no effect on electron affinity. This could be because fluorine also acts as pi‐donor, thus, a pi‐acceptor substituent may have a greater impact on the energy levels. To test this hypothesis, we synthesized three new ADP‐based complexes with nitrile substitutions. Cyclic voltammetry shows that the nitrile substitutions indeed anodically shifts the reduction potentials, leading to increased electron affinity. The shift was ≈ 0.3 V for the p‐distal phenyl substitution and 0.16V for the p‐phenylethynyl substitution. Nitrile substitution was also found to improve electron accepting ability and electron mobility in diodes, as compared to the un‐substituted analogues.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Synthesis and Properties of Azadipyrromethene‐Based Complexes with Nitrile Substitution

et al. 2020

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“…The fluorinated complexes were tested as acceptors in OPVs using P3HT as the donor, and the optimized results are summarized in Table . First, P3HT : Zn(WS3) 2 now has a PCE of 2.5 % instead of 4 %.…”

Section: Large Molecular Acceptor: Non‐planar Shapementioning

confidence: 99%

Designing Alternative Non‐Fullerene Molecular Electron Acceptors for Solution‐Processable Organic Photovoltaics

Sauvé

2019

The Chemical Record

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Until recently, solution‐processable organic photovoltaics (OPVs) mainly relied on fullerene derivatives as the n‐type material, paired with a p‐type conjugated polymer. However, fullerene derivatives have disadvantages that limit OPV performance, thus fueling research of non‐fullerene acceptors (NFAs). Initially, NFAs showed poor performance due to difficulties in obtaining favorable blend morphologies. One example is our work with 2,6‐dialkylamino core‐substituted naphthalene diimides. Researchers then learned to control blend morphology by NFA molecular design. To limit miscibility with polymer while preventing excessive self‐aggregation, non‐planar, twisted or 3D structures were reported. An example of a 3D structure is our work with homoleptic zinc(II) complexes of azadipyrromethene. The most recent design is a planar A‐D‐A conjugated system where the D unit is rigid and has orthogonal side chains to control aggregation. These have propelled power conversion efficiencies (PCEs) to ∼14 %, surpassing fullerene‐based OPVs. These exciting new developments prompt further investigations of NFAs and provide a bright future for OPVs.

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Correlating Ultrafast Dynamics, Liquid Crystalline Phases, and Ambipolar Transport in Fluorinated Benzothiadiazole Dyes

Boehme

Yimga

Frick

et al. 2021

Adv Elect Materials

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organic semiconductors (OSCs) that can be easily processed with low-cost, largethroughput fabrication techniques. While high carrier mobilities are generally desirable, optoelectronic devices, such as organic light-emitting diodes [1] and organic photovoltaics, [2] specifically profit from ambipolar transport, i.e., balanced electron and hole transport. However, the majority of OSCs are predominantly unipolar, and demonstrate higher hole mobilities than electron mobilities. [3] Therefore, device fabrication typically requires the deposition of multiple unipolar OSCs to achieve the desired electrical properties, thereby complicating the fabrication protocols.Soluble small-molecule semiconductors that form crystalline films have the potential to combine the advantages of high chemical purity and superior (opto)electronic properties with good processability. However, crystalline organic films formed from soluble small molecules often display poor structural and thermal integrity, as well as lower carrier mobilities compared to nonsoluble small-molecule derivatives. In other words, processability generally comes at the expense of both reduced thermal and mechanical stability, as well as electrical transport.In this study, we synthesized soluble small-molecule dyes that form crystalline films at room temperature, but A key challenge in the field of organic electronics is predicting how chemical structure at the molecular scale determines nature and dynamics of excited states, as well as the macroscopic optoelectronic properties in thin film. Here, the donor-acceptor dyes 4,7-bis[5-[4-(3-ethylheptyl)-2,3-difluorophenyl]-2-thienyl]-2,1,3-benzothiadiazole (2,3-FFPTB) and 4,7-bis[5-[4-(3-ethylheptyl)-2,6-difluorophenyl]-2-thienyl]-2,1,3-benzothiadiazole (2,6-FFPTB) are synthesized, which only differ in the position of one fluorine substitution. It is observed that this variation in chemical structure does not influence the energetic position of the molecular frontier orbitals or the ultrafast dynamics on the FFPTB backbone.However, it does result in differences at the macroscale, specifically regarding structural and electrical properties of the FFPTB films. Both FFPTB molecules form crystalline films at room temperature, whereas 2,3-FFPTB has two ordered smectic phases at elevated temperatures, and 2,6-FFPTB does not display any liquid crystalline phases. It is demonstrated that the altered location of the fluorine substitution allows to control the electrostatic potential along the molecular backbone without impacting molecular energetics or ultrafast dynamics. Such a design strategy succeeds in controlling molecular interactions in liquid crystalline phase, and it is shown that the associated molecular order, or rather disorder, can be exploited to achieve ambipolar transport in FFPTB films.

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Fluorination increases the electron mobility of zinc azadipyrromethene-based electron acceptors and enhances the performance of fullerene-free organic solar cells

Abstract: Strategic fluorination of non-planar electron acceptors reduces bimolecular recombination in OPVs and significantly enhances the electron mobility to ∼10−3 cm2 V−1 s−1 in diodes.

Cited by 12 publications

References 42 publications

Synthesis and Properties of Azadipyrromethene‐Based Complexes with Nitrile Substitution

Synthesis and Properties of Azadipyrromethene‐Based Complexes with Nitrile Substitution

Designing Alternative Non‐Fullerene Molecular Electron Acceptors for Solution‐Processable Organic Photovoltaics

Correlating Ultrafast Dynamics, Liquid Crystalline Phases, and Ambipolar Transport in Fluorinated Benzothiadiazole Dyes

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