Acceptor Block Research Articles

Synthesis of All-Conjugated ABA and AB-type Donor-Acceptor Block Copolymers and Their Application in All-Polymer Solar Cells

ABSTRACTIn this work, we report the synthesis of all-conjugated donor-acceptor block copolymers via a externally initiated Kumada catalyst-transfer polycondensation (KCTP) method. In the first step, electron acceptor blocks, poly(naphthalene diimide)s (PNDIs), were prepared via the Stille coupling polycondensation. Then, P3HT blocks were polymerized by KCTP initiated by Ni(COD)2 activated PNDI complexes. Therefore, a series of ABA (P3HTs were initiated from both ends of PNDI) and AB-type (P3HT was initiated from one end of PNDI) block copolymers were successfully synthesized. Before fabrication of all-polymer solar cells, the morphologies and crystalline behaviors of the block copolymers were extensively investigated as a function of thermal annealing and the main chain composition of PNDI block. As a control, the crystalline behaviors of the physical blends of P3HT and PNDIs were also reported. Finally, all-polymer solar cells were fabricated by using the block copolymers as the single active component or as surfactants. A PCE of 0.11 % with Voc=0.46 V, Jsc=0.50 mA/cm2, and FF=0.46 was recorded by using the donor-acceptor all-conjugated block copolymer as the single active component.

A novel complementary absorbing donor–acceptor pair in block copolymers based on single material organic photovoltaics

We report on the first synthesis of a highly crystalline donor–acceptor low band gap block copolymer by using diketopyrrolopyrrole (DPP) as a low band gap block and perylenebisimide (PDI) as a strong acceptor block.

Development of Large Band-Gap Conjugated Copolymers for Efficient Regular Single and Tandem Organic Solar Cells

We demonstrated the synthesis and characterization of two conjugated copolymers, PBDTFBZO and PBDTFBZS, consisting of dialkylthiol substituted benzo[1,2-b:4,5-b']dithiophene donor and monofluorinated benzotriazole acceptor blocks. The resulting copolymers show large band gaps, deep HOMO and LUMO energy levels. Improved V(oc), J(sc), and FF were obtained at the same time to increase overall efficiencies of their single and tandem polymer solar cells. The enhanced V(oc) can be ascribed to a low-lying HOMO energy level by incorporating dialkylthiol and fluorine substituents on the polymer backbone. The improvement in J(sc) and FF are likely due to high carrier mobility, suppressed charge recombination, and fine nanostructure morphology. A 7.74% PCE was achieved from the regular single device based on PBDTFBZS:PC71BM blend film with 3% 1,8-diiodooctane (DIO) additive. In combination with low band gap diketopyrrolopyrrole (DPP)-based copolymer, tandem devices based on PBDTFBZS exhibited high PCE up to 9.40%. The results indicate that PBDTFBZO and PBDTFBZS are promising polymer donor materials for future application of large-area polymer solar cells.

Phase Separation in the Melt and Confined Crystallization as the Key to Well-Ordered Microphase Separated Donor–Acceptor Block Copolymers

Microphase-separated donor–acceptor block copolymers have been discussed as ideal systems for morphology control in organic photovoltaics. Typical microphases as known from coil–coil systems were not observed in such systems due to crystallization dominating over microphase separation. We show how this problem can be overcome by the synthesis of high molecular weight block copolymers leading to a high enough χN parameter and microphase separation in the melt. A combination of copper-catalyzed azide-alkyne click reaction and nitroxide mediated radical polymerization (NMRP) was used for the synthesis of donor–acceptor poly(3-hexylthiophene)-block-poly perylene bisimide acrylate (P3HT-b-PPerAcr) block copolymers. With this synthetic strategy, high molecular weights are possible and no triblock copolymer byproducts are formed, as observed with former methods. Two different block copolymers with a high molecular weight P3HT block of 19.7 kg/mol and a PPerAcr content of 47 and 64 wt % were obtained. X-ray scatt...

Correlation between structure and photovoltaic performance of a series of furan bridged donor–acceptor conjugated polymers

A series of donor–acceptor (D–A) polymers based on furan-bridged benzodithiophene and different acceptor blocks were designed and synthesized. By incorporating various acceptors with differing electron-withdrawing abilities into the same polymer backbone, we were seeking to reveal the correlation between molecular structures and the corresponding film morphology as well as photovoltaic performance. The experimental results and theoretical calculations indicate that the selection of acceptor units has significant impacts on the polymer energy levels and backbone coplanarity, leading to differing intermolecular packing. By using atomic force microscopy and transmission electron microscopy, we also observed that the size and topology of the alkyl-chains on acceptors can tune the polymer solubility and result in different film morphology. As a result of optimized morphology, we demonstrated power conversion efficiencies over 5% for the new polymer based devices, which are among the highest efficiencies of reported furan bridged D–A polymers.

Synthesis of all-conjugated donor–acceptor block copolymers and their application in all-polymer solar cells

Electron donor–acceptor triblock and diblock copolymers have attracted considerable interest due to their potential applications in all-polymer solar cells as single-active components or surfactants. However, the number of donor–acceptor block copolymers has lagged behind that of the rod–coil and rod–rod block copolymers due to their synthetic difficulties. This minireview highlights the recent advances in the synthetic strategies for the all-conjugated donor–acceptor block copolymers and their application in all-polymer solar cells.

All-Polymer Solar Cells Based on Fully Conjugated Block Copolymers Composed of Poly(3-hexylthiophene) and Poly(naphthalene bisimide) Segments

Fully conjugated donor–acceptor block copolymers composed of poly(3-hexylthiophene) and poly(naphthalene bisimide) segments, P3HT-PNBI-P3HTs, were synthesized using quasi-living Grignard metathesis polymerization and the Yamamoto coupling reaction. Broad absorption in a range of 350–850 nm, which corresponded to the optical band gap of 1.46 eV, was observed for the P3HT-PNBI-P3HT thin films. In addition, the optical band gap decreased to 1.38 eV (the light absorption band extended to 893 nm) by thermal annealing, which was much smaller than those of previously reported donor–acceptor block copolymers (1.6–1.8 eV). The annealed P3HT:P3HT-PNBI-P3HT blend film (1:1 by weight) also exhibited broad absorption in the range of 350–950 nm. Cyclic voltammetry demonstrated that the P3HT-PNBI-P3HT thin films exhibited the oxidation and reduction properties derived from the P3HT and PNBI segments. The HOMO and LUMO levels were in the range of 5.57–5.60 and 4.22–4.27 eV, respectively. All-polymer solar cells using the...

A Modular Strategy for Fully Conjugated Donor–Acceptor Block Copolymers

A novel strategy for the synthesis of fully conjugated donor-acceptor block copolymers, in a single reaction step employing Stille coupling polymerization of end-functional polythiophene and AA + BB monomers, is presented. The unique donor-acceptor structure of these block copolymers provides a rich self-assembly behavior, with the first example of a fully conjugated donor-acceptor block copolymer having two separate crystalline domains being obtained.

Fullerene-Functionalized Donor–Acceptor Block Copolymers through Etherification as Stabilizers for Bulk Heterojunction Solar Cells

A new synthetic method for the covalent linking of fullerenes to polymers is introduced. The Bingel-reaction was used to prepare bromine-functionalized fullerene building blocks that could be covalently linked to hydroxyl groups of model copolymers by the cesium carbonate promoted Williamson ether synthesis. Subsequently, block copolymers with a second block based on styrene and hydroxystyrene or hydroxyethyl methacrylate could be synthesized with a poly(3-hexylthiophene)–TEMPO macroinitiator through NMRP. Fullerene derivatives were linked to these polymers in a controlled manner and donor–acceptor block copolymers with high fullerene contents of near 50 wt % were achieved.

Polystyrene-Based C60 Acceptor Copolymers through Azide-Alkyne Click Chemistry Approaches

Poly(styrene-r-propargyloxy styrene) with varying molecular weights is prepared by means of a nitroxide-mediated radical polymerization and a malonate is “clicked” to it. Fullerene C60 is reacted under Bingel conditions with the polymer and can be covalently bound to its side chains. These polymers show good solubility in common organic solvents and intense studies are performed to determine the degree of substitution with fullerenes. A loading of around 15 to 20 wt% is detected by thermogravimetric analyses (TGA). These materials might be promising as the acceptor component for donor–acceptor block copolymers. Furthermore, new bromine- and organo-azide-functionalized methano fullerenes are prepared and characterized.

Frontier orbital and morphology engineering of conjugated polymers and block copolymers for potential high efficiency photovoltaics

The photoelectric power conversion efficiencies of currently reported organic/polymeric photovoltaic materials are still relatively low (typically less than 9% under AM 1.5 and one Sun intensity), and the three major losses are still severe, i.e., the ‘photon loss’ due to mismatch of materials energy gaps versus the sunlight photon energies, the ‘exciton loss’ and the ‘carrier loss’ due to poor solid state morphologies of existing polymeric donor/acceptor binary systems. Therefore, both molecular frontier orbitals (HOMOs, LUMOs) and phase morphologies of the photovoltaic polymers need to be optimized to further enhance the efficiency. In this presentation, our recent efforts on frontier orbital and energy gap engineering and terminal functionalizations of conjugated polymer blocks, and the donor-bridge-acceptor type block copolymer approaches will be reviewed. For instance, an earlier developed (DBAB)n block copolymer system (where D represents a conjugated donor block, A represents a conjugated acceptor block, and B represents a non-conjugated bridge unit) exhibited much better photovoltaic properties compared to the corresponding simple D/A blend system. Recently, a new DBA conjugated block copolymer system based on mono-functionalized monomers has also been synthesized. Additionally, a series of terminal functional and sulfone-containing conjugated polymers with evolving frontier orbital energy levels and gaps have recently been designed, synthesized, and studied. The HOMO/LUMO energy gaps of these new polymers were in a range of 1.5–2.6 eV, which are very attractive for solar energy applications. The terminal functional groups (aldehyde or phosphonate) make these polymer blocks potentially ideal candidates for the development of donor/acceptor block copolymer supra-molecular nanostructures for a variety of optoelectronic applications.

Interplay between solid-state organization and optical properties of thin films of poly-arylene-vinylene and -difluorinated vinylene: Fullerene blends

Nowadays considerable efforts are devoted to the synthesis of low bandgap conjugated polymers for application in organic polymer solar cells. A large variety of low bandgap polymers are prepared by alternating copolymerization of electron-donating donor and electron-withdrawing acceptor units. The interaction between these two units can reduce the polymer bandgap, increasing the sunlight absorption. Benzothiadiazole is commonly used as acceptor block unit in low bandgap polymers. In this contribution we investigate the supramolecular organization and optical properties of thin films of conjugated polymers consisting of benzothiadiazole and thiophene with electron-withdrawing difluorovinylene, and electron-donating vinylene substituents. Atomic force microscopy and spectroscopic ellipsometry are exploited for the analysis of the morphology and optical transitions, respectively. It is found that F-atoms in the vinylene unit yield a blue-shift of the absorption peaks of 0.2eV respect to the hydrogenated polymer and an increase in the absorption coefficient of fluorinated polymers, which indicates their potential application as photovoltaic material. The morphology evolution of the conjugated polymers blended with a fullerene derivate ([6,6]-phenyl C61-butyric acid methyl ester, PCBM) is also investigated by atomic force microscopy.

Optoelectronic Properties and Charge Transfer in Donor–Acceptor All-Conjugated Diblock Copolymers

All-conjugated block copolymers, which can self-assemble into well-ordered morphologies, provide exciting opportunities to rationally design and control the nanoscale organization of electron–donor and electron–acceptor moieties in optoelectronic active layers. Here we report on the steady-state and time-resolved optical characterization of block copolymer films and solutions containing poly(3-hexylthiophene) as the donor block and poly(9,9-dioctylfluorene) with and without copolymerization with benzothiadiazole as the acceptor block. Transient absorption measurements suggest rapid charge transfer occurs in both systems, with higher efficiency observed in the latter composition. These results indicate that this class of materials has promise in preparing highly ordered bulk heterojunction all-polymer organic photovoltaic devices.

Poly(3-hexylthiophene)-block-poly(pyridinium phenylene)s: Block Polymers of p- and n-Type Semiconductors

Conjugated crystalline−crystalline donor−acceptor−donor block copolymer semiconductors, with regioregular poly(3-hexylthiophene) as a donor (p-type) block and poly(pyridinium pheneylene) as an acceptor (n-type) block within the backbone, were produced by sequential Grignard metathesis synthesis of poly(3-hexylthiophene), a Yamamoto-type cross-coupling polymerization−cyclization sequence. These conjugated block copolymers are soluble in organic solvents and display broad optical absorption bands extending close to the near-infrared region. They show reversible ambipolar redox properties with high electron affinities of 3.8−4.0 eV as well as useful ionization potentials of 5.1 eV that are characteristic of the respective blocks. Block copolymers from p- and n-type organic semiconductors are of interest for the formation of nanostructured bulk heterojunctions in photovoltaic devices.

Overcoming excitonic bottleneck in organic solar cells: electronic structure and spectra of novel semiconducting donor–acceptor block copolymers

A novel class of organic semiconductors aimed at improving the efficiency of organic photovoltaic devices is investigated by an ab initio electronic structure theory. Two conjugated block copolymers composed of chemically bound donor and acceptor blocks show substantial charge transfer upon photoexcitation, suggesting that the optically excited states are separated charge pairs rather than strongly interacting charges forming excitons. In contrast, little charge transfer is seen in the ground electronic state. The optical cross-sections of the charge separated states are quite high due to a good overlap of the tails of the ground and excited state wavefunctions. The absorption spectra of the systems cover visible spectrum and extend to the infrared, suggesting good prospects for light harvesting. The calculation results indicate that the proposed class of semiconducting molecular heterojunctions may overcome the exciton bottleneck problem in organic photovoltaic materials.

Donor–acceptor block copolymers for photovoltaic applications

Extensive research activities in polymer synthesis and device engineering have been devoted to the development of donor–acceptor (D–A) bulk heterojunction solar cells in the last years. In such devices, several photophysical processes occur all of which have to be optimized for efficient operation. First, excitons created upon light absorption need to reach the D/A interface within their exciton diffusion length (10– 20 nm), where they may dissociate into holes and electrons. Subsequent charge transport and finally charge collection at the electrodes can occur, given that co-continous pathways of donor and acceptor domains are provided. Owing to the small exciton diffusion lengths and the required optical absorption length of 100–200 nm, vertically aligned pathways with a high aspect ratio of either phase should percolate through the film. The morphologies resulting from this ideal situation resemble those of vertically oriented microphase separated block copolymer thin films, and hence suggest the importance of D–A block copolymers for organic photovoltaics. Furthermore, the covalent bond between the donor and acceptor blocks is not only desired to improve morphology control, but also to enhance long term stability of the device. The potential of block copolymers with electronic functionality to microphase separate into well-defined microstructures with several tens of nanometers in size thus addresses the morphological requirements mentioned above. This article gives an overview of donor–acceptor block copolymers and summarises recent developments of this field.

Creation, validation, and quantitative analysis of protein expression in vascular tissue microarrays

Tissue microarrays (TMAs) are collections of multiple tissue cores placed in parallel in a single acceptor block and traditionally used to investigate protein expression in neoplastic tissues. We validated the use of TMAs to investigate protein expression in vascular segments. Vascular tissues were collected from 100 adult subjects undergoing autopsy. A diverse set of vessels were harvested and arrayed over 17 TMAs. A total of 1377 unique tissues, each with a 1.5-mm feature size, were analyzed using histochemical and immunohistochemical (IHC) diaminobenzidine (DAB) methods. Histomorphometric analysis of vascular disease demonstrated the TMA features captured the majority of the vascular alterations (intimal hyperplasia and atherosclerosis) seen in the original blood vessel section. Measurements of IHC staining intensity based on color deconvolution were used to quantify antigen abundance in defined regions of interest (ROI). Validation was performed using antibodies to connective tissue growth factor (CTGF), receptor for advanced glycation end products (AGER/RAGE), and matrix metalloproteinase 3 (MMP-3). IHC staining was highly correlated between duplicate features from the same vascular site over these three proteins. This study validates the use of TMA technology to investigate the vascular wall utilizing staining intensity data.

Donor−Acceptor Poly(thiophene-block-perylene diimide) Copolymers: Synthesis and Solar Cell Fabrication

Donor−acceptor diblock copolymers, composed of regioregular poly(3-hexylthiophene) (rrP3HT) as the electron donor block and poly(perylene diimide acrylate) (PPDA) as the electron acceptor block, were prepared and used to fabricate a solar cell. Vinyl-terminated rrP3HT was synthesized by Grignard metathesis polymerization and converted to an alkoxyamine macroinitiator. This polythiophene macroinitiator was used in controlled free radical polymerization of a perylene diimide-containing acrylate. The targeted donor−acceptor diblock copolymers were prepared with low-to-moderate polydispersity indices (1.2−1.4) and molecular weights sufficiently high for producing films by spin-coating. These copolymers showed efficient photoluminescence quenching in the solid state, indicative of charge separation, and were used to produce a solar cell with power conversion efficiency of 0.49%.

Charge separation and recombination in self-organizing nanostructured donor–acceptor block copolymer films

Download options Please wait... Article information DOI https://doi.org/10.1039/B905708K Article type Paper Submitted 20 Mar 2009 Accepted 19 May 2009 First published 29 Jun 2009 Download Citation J. Mater. Chem., 2009,19, 5436-5441 BibTex EndNote MEDLINE ProCite ReferenceManager RefWorks RIS Permissions Request permissions Charge separation and recombination in self-organizing nanostructured donor–acceptor block copolymer films S. King, M. Sommer, S. Huettner, M. Thelakkat and S. A. Haque, J. Mater. Chem., 2009, 19, 5436 DOI: 10.1039/B905708K To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page. If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given. If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page. Read more about how to correctly acknowledge RSC content. Search articles by author Simon King Michael Sommer Sven Huettner Mukundan Thelakkat Saif A. Haque

Controlled solvent vapour annealing for polymer electronics

Solvent vapour annealing (SVA) is demonstrated as an attractive method to anneal polymer blend and block copolymer thin films at low temperatures. It is especially suitable for organic electronics, where sensitive materials with strong intermolecular interactions are used. We demonstrate the effect of solvent vapour exposure on the film properties of a perylene bisimide acrylate (PPerAcr) side-chain polymer with strong crystallinity at the perylene bisimide moieties. We record the film thickness, light absorption and fluorescence as a function of the relative solvent vapour pressure. At a certain threshold of relative solvent vapour pressure, we observe a disruption of the π–π stacking, which is responsible for perylene bisimide crystallisation. This leads to an increase in the polymer-chain mobility and therefore to changes in the film morphology. The results are applied to a film of a donor–acceptor block copolymer carrying PPerAcr segments, and the influence of solvent annealing on the nanoscale morphology is demonstrated.