Ying Jiang’s research while affiliated with Stanford University and other places

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Publications (9)


5,11-Conjugation-extended low-bandgap anthradithiophene-containing polymer exhibiting enhanced thin-film order and field-effect mobility
  • Article

June 2012

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21 Reads

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19 Citations

Chemical Communications

Ying Jiang

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Zhenan Bao

Anthradithiophene was incorporated in a polymer structure by extending its conjugation from the 5,11-positions, through in situ desilylation followed by acetylenic coupling with a dibromo-monomer. The resulting polymer showed largely redshifted order in a thin film as well as order in thin film, forming lamellar structures out of the substrate plane. As a result, it exhibits field-effect hole mobilities, on the order of 0.1 cm(2) V(-1) s(-1), a ten to hundred-fold improvement as compared to previous acene-containing polymers.


Fig. 1 
Table 1 Electrochemical and photophysical properties of polymers PnBTs and PnCPDTs
Fig. 2 
Fig. 3 
Fig. 4 5 m m  5 m m AFM topographs of PnBT-2,9 films cast from chloroform (a) by drop-casting on OTS-treated surface and (b) by spin- casting on PTS-treated surface. 

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Impact of regioregularity on thin-film transistor and photovoltaic cell performances of pentacene-containing polymers
  • Article
  • Full-text available

February 2012

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111 Reads

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15 Citations

Journal of Materials Chemistry

Regioregular pentacene-containing polymers were synthesized with alkylated bithiophene (BT) and cyclopentadithiophene (CPDT) as comonomers. Among them, 2,9-conjugated polymersPnBT-2,9 and PnCPDT-2,9 achieved the best performance in transistor and photovoltaic devices respectively. The former achieved the most highly ordered structures in thin films, yielding ambipolar transistor behavior with hole and electron mobilities up to 0.03 and 0.02 cm2 V−1 s−1 on octadecylsilane-treated substrates. The latter achieved photovoltaic power conversion efficiencies up to 0.33%. The impact of regioregularity and direction of conjugation-extension (2,9 vs. 2,10), on thin-film order and device performance has been demonstrated for the pentacene-containing polymers for the first time, providing insight towards future functional material design.

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Synthesis of regioregular pentacene-containing conjugated polymers

May 2011

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14 Reads

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19 Citations

Journal of Materials Chemistry

We report the synthesis and characterization of a new class of regioregular pentacene-containing conjugated polymersvia our synthetic routes reported previously. We found that our regioregular pentacenepolymers showed improved ordering than their regiorandom counterpart as well as ambipolar OFET performance.


2,9-Dibromopentacene: Synthesis and the role of substituent and symmetry on solid-state order

December 2010

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22 Reads

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10 Citations

Synthetic Metals

We have developed an effective synthetic route for 2,9-dibromopentacene, opening up new possibilities for future derivatization of pentacene. We also present the fundamental properties. Thin-film and single-crystal field-effect transistor results demonstrate a decrease in apparent charge transport efficiency with decreasing symmetry. The trend in symmetry was further correlated to single-crystal structural analysis, which implied that reduction in symmetry also reduced solid-state order. It is likely that this reduction in order is responsible for the diminished performance in the solid-state films and crystal, despite a reduction in overall tilt angle of the molecules relative to one another. Combined with previous studies, this work provides a more complete perspective on the interplay of symmetry, energetic, and intermolecular interactions in the macroscopic properties of solid-state organic electronic materials.


Anthradithiophene-Containing Copolymers for Thin-Film Transistors and Photovoltaic Cells

July 2010

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37 Reads

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52 Citations

Macromolecules

We synthesized anthradithiophene−cyclopentadithiophene conjugated copolymers via Stille coupling. The anthradithiophene core was verified to be superior in stability compared to pentacene toward Diels−Alder cycloaddition and therefore more compatible with fullerenes, acceptor material commonly used in bulk heterojunction (BHJ) photovoltaic cells. The polymers exhibit high film absorption coefficients of 105 cm−1, an order of magnitude higher than previously reported anthradithiophene−dialkylfluorene copolymers. Short-circuit currents exceeding 5 mA/cm2 and a BHJ device efficiency close to 1% were achieved when device morphology was improved with diiodooctane as a solvent additive. This is the highest power conversion efficiency achieved by an acene-containing polymer so far.


Synthesis and Characterization of Pentacene− and Anthradithiophene− Fluorene Conjugated Copolymers Synthesized by Suzuki Reactions

October 2008

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80 Reads

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60 Citations

Macromolecules

We have synthesized new types of pentacene- and anthradithiophene-dialkylfluorene conjugated copolymer via Suzuki cross-coupling polymerization. The polymer chemical structures and molecular weights were characterized by H-1 NMR, C-13 NMR, and gel permeation chromatography (GPC). Fundamental properties, such as electrochemical and optical behavior, were studied using cyclic voltammetry (CV) and UV-vis absorption (UV-vis) to estimate the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels as well as their optical bandgaps. Both polymers exhibit relatively low bandgaps and their high solubility in common halogenated organic solvents. They were successfully incorporated into photovoltaic cells, giving a power efficiency up to 0.68%. This is the first acene-containing conjugated polymer solar cell.


Synthesis and Design of Acene-Containing Polymers for Organic Photovoltaics

June 2008

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10 Reads

Triisopropylethynyl derivatives of pentacene (TIPSEP) and anthradithiophene (TIPSEAdT) copolymerized with diethynylbenzene and fluorene via Sonogashira and Suzuki coupling show optical bandgaps between 1.6 and 2.0 eV. TIPSEAdT-9,9-dioctylfluorene yielded preliminary photovoltaic power conversion efficiency of 0.69%. Article not available.


Fig. 1 Representative I-V curves of OTFTs of 1 . ( a , c ) measurements performed in dry, inert environment. ( b , d ) same device tested in air. 
Fig. 2 . Tapping mode AFM of annealed films of 1 ( a ), 3 ( b ), 4 ( c ) and 5 ( d ). A shows clearly defined grains, while b - d are less textured. ( e ) XRD spectra of the films. The gradual disappearance of the peak at ~22.66 Å indicates disorder increases with Mw ( 1 - 4 ) or with incorporation of bulky side chains ( 5 ). Insets are GIXD slices of 1 and 4 showing the same decrease in film order. ACTP-F copolymers may have limitations in solar cells due to low absorption coefficients ( α ). For example, films from 5 have α ~1.6 x 10 4 cm -1 at 600 nm, compared to ca . 1.8 x 10 5 cm -1 for P3HT. 39 By integrating the absorption spectrum of 
Fig. 3 I-V characteristic for the solar cell made from 5, 1:4 polymer:PC [61] BM by weight, optimized with an LiF/Al cathode.
2007 GCEP Report Project title: Advanced Materials and Devices for Low Cost and High Performance Organic Photovoltaic Cells

Exciton harvesting is of fundamental importance for the efficient operation of organic photovoltaic devices. The quantum efficiencies of many organic and hybrid organic- inorganic devices are still limited by low exciton harvesting efficiencies. This problem is most apparent in planar heterostructures that suffer from a direct tradeoff between light absorption and exciton harvesting. One approach to overcome small diffusion lengths is the use of triplet excitons. We have an ongoing project investigating pentacene/C60 solar cells to determine if triplets are the dominant exciton species following photoexcitation. Simulations of exciton harvesting suggest that excitons in pentacene are triplets. These triplets are likely formed by an exciton fission route which further has implications for beating the Shockley-Queisser limit and experiments are ongoing to verify this. In addition to using triplets to harvest excitons over long distances, we have developed a new scheme using long range resonant energy transfer to harvest singlet excitons over 25 nm away from the donor-acceptor interface in organic solar cells using resonant energy transfer. These results represent dramatic improvements over our previous findings and show that this scheme holds promise for the future design of highly efficient organic photovoltaics. We present theory and experiment demonstrating a scheme to harvest singlet excitons over 25 nm away from a donor-acceptor interface using resonant energy transfer. Improvement in materials choice could yield effective diffusion lengths as large as 40 nm using long-range transfer, while minimizing the energy loss to less than 0.1 eV making this a promising approach for developing highly efficient organic photovoltaics. Finally, we have successfully synthesized several new low-band gap polymers. Several of these polymers have bandgap of 1.7 eV or lower. Evaluation of the performance of these new materials is underway.


Project title: Advanced Materials and Devices for Low Cost and High Performance Organic Photovoltaic Cells

37 Reads

Exciton harvesting is of fundamental importance for the efficient operation of organic photovoltaic devices. The quantum efficiencies of many organic and hybrid organic- inorganic devices are still limited by low exciton harvesting efficiencies. This problem is most apparent in planar heterostructures that suffer from a direct tradeoff between light absorption and exciton harvesting. One approach to overcome small diffusion lengths is the use of triplet excitons. We have an ongoing project investigating pentacene/C60 solar cells to determine if triplets are the dominant exciton species following photoexcitation. Simulations of exciton harvesting suggest that excitons in pentacene are triplets. These triplets are likely formed by an exciton fission route which further has implications for beating the Shockley-Queisser limit and experiments are ongoing to verify this. In addition to using triplets to harvest excitons over long distances, we have developed a new scheme using long range resonant energy transfer to harvest singlet excitons over 25 nm away from the donor-acceptor interface in organic solar cells using resonant energy transfer. These results represent dramatic improvements over our previous findings and show that this scheme holds promise for the future design of highly efficient organic photovoltaics. We present theory and experiment demonstrating a scheme to harvest singlet excitons over 25 nm away from a donor-acceptor interface using resonant energy transfer. Improvement in materials choice could yield effective diffusion lengths as large as 40 nm using long-range transfer, while minimizing the energy loss to less than 0.1 eV making this a promising approach for developing highly efficient organic photovoltaics. Finally, we have successfully synthesized several new low-band gap polymers. Several of these polymers have bandgap of 1.7 eV or lower. Evaluation of the performance of these new materials is underway.

Citations (6)


... A representative case is provided by pentacenecontaining copolymers, which are typically regiorandom 62,63 , due to difficulties in separating regio-isomeric dibrominated precursors. The copolymerization of pure 2,9-and 2,10dibromopentacene derivatives with distannyled bithiophene comonomer gives the well-defined RR copolymers PnBT-2,9 and PnBT-2,10 ( Fig. 3a) 64 . In contrast, mixed dibromopentace starting materials and the same bithiophene reactant yield the regiorandom counterpart PnBT-RRa. ...

Reference:

Regioregular narrow-bandgap-conjugated polymers for plastic electronics
Impact of regioregularity on thin-film transistor and photovoltaic cell performances of pentacene-containing polymers

Journal of Materials Chemistry

... Pentacene-based copolymers constructed via attachments at the 2,9-or 2,10-positons are also worth considering within the context of structural precision 78 . A synthetic route to obtain pure 2,9-and 2,10-dibromopentacene precursors was reported, see Fig. 3a, which enabled the synthesis of regioregular pentacene-containing copolymers 80 . Despite the relatively low n-type mobility (10 À 4 -10 À 5 cm 2 V À 1 s À 1 ) of the resulting RR copolymers, these values are considerably higher than what is obtained when using the regiorandom counterpart (8 Â 10 À 7 cm 2 V À 1 s À 1 ). ...

Synthesis of regioregular pentacene-containing conjugated polymers
  • Citing Article
  • May 2011

Journal of Materials Chemistry

... In the study of contact propensities in the crystal structures of halogenated organic molecules [44], the packing of the C 22 H 12 Br 2 molecule (OKANOE [32,52]) was identified as having a particularly high Br···Br contact enrichment. The molecule 2,3-dibromopentacene is a very long rigid elongated molecule bearing two Br atoms on its extremities where the shape of the molecule plays an essential role in the crystal packing formation. ...

2,9-Dibromopentacene: Synthesis and the role of substituent and symmetry on solid-state order
  • Citing Article
  • December 2010

Synthetic Metals

... Second, the use of homogeneous palladium catalysts in polymerization reactions could cause a high level of palladium impurity which is firmly embedded in the polymer chains formed because of palladium leaching [27,28]. The post-treatment of polymers frequently required the use of a palladium scavenger to achieve a high purity [28][29][30], and the process for purifying polymers is quite tedious, thereby limiting application of such catalytic systems in large-scale preparation of highly purified polymers. Therefore, from the viewpoint of green and sustainable chemistry, development of a recyclable heterogeneous palladium-catalyzed carbonylative polycondensation for the preparation of PAIs is highly desirable. ...

Anthradithiophene-Containing Copolymers for Thin-Film Transistors and Photovoltaic Cells
  • Citing Article
  • July 2010

Macromolecules

... For example, Bao et al. showed conjugated polymers of pentacene are air-stable and solution-processable, unlike pentacene small molecules. 16,17 This breakthrough has inspired the emergence of various functionalized acene oligomers and polymers that are both soluble and stable. 5,8,[18][19][20][21][22][23] In terms of electronic structure, recent studies have demonstrated that acene-based polymers exhibit non-linear band gap alterations as the size of the carbocyclic acene unit changes, and a zero-band gap conjugated polymer of pentacene was synthesized. ...

Synthesis and Characterization of Pentacene− and Anthradithiophene− Fluorene Conjugated Copolymers Synthesized by Suzuki Reactions
  • Citing Article
  • October 2008

Macromolecules

... However, in relation to pentacene-based polymers, 15-17 even fewer conjugated polymers containing the more stable ADT derivatives have been prepared. [18][19][20][21][22] Here we report the synthesis of a new series of conjugated copolymers (1-5, Fig. 1) that are accessible through a metal catalyzed cross-coupling reaction at the 5 and 11 positions of dihexylanthradithiophene (DHADT). This strategy is different than the traditional method to create 5,11-functionalized ADT polymers, which rely on nucleophilic substitutions on anthradithiophene quinones. ...

5,11-Conjugation-extended low-bandgap anthradithiophene-containing polymer exhibiting enhanced thin-film order and field-effect mobility
  • Citing Article
  • June 2012

Chemical Communications