High-performance, solution-processed transistors fabricated from semiconducting polymers containi... more High-performance, solution-processed transistors fabricated from semiconducting polymers containing indacenodithiohene repeat units are described. The bridging functions on the backbone contribute to suppressing large-scale crystallization in thin films. However, charge carrier mobilities of up to 1 cm2/(V s) for a benzothiadiazole copolymer were reported and, coupled with both ambient stability and long-wavelength absorption, make this family of polymers particularly attractive for application in next-generation organic optoelectronics.
Thieno [3, 2-b] thienobis (silolothiophene), a new electron rich hexacyclic monomer has been synt... more Thieno [3, 2-b] thienobis (silolothiophene), a new electron rich hexacyclic monomer has been synthesized and incorporated into three novel donor-acceptor low-bandgap polymers. By 10 carefully choosing the acceptor co-monomer, the energy levels of the polymers could be modulated and high power conversion efficiencies of 5.52% were reached in OPV devices.
Two novel indacenodithiophene (IDT) based donor-acceptor conjugated polymers for use in organic f... more Two novel indacenodithiophene (IDT) based donor-acceptor conjugated polymers for use in organic field effect transistors and photovoltaic devices are synthesized and characterized. The effect of inclusion of two fluorine atoms on the acceptor portion of the polymer is thoroughly investigated via a range of techniques. The inductively withdrawing and mesomerically donating properties of the fluorine atoms result in a decrease of the HOMO, with little effect on the LUMO as demonstrated through DFT analysis.
We describe a series of highly soluble diketo pyrrolo-pyrrole (DPP)-bithiophene copolymers exhibi... more We describe a series of highly soluble diketo pyrrolo-pyrrole (DPP)-bithiophene copolymers exhibiting field effect hole mobilities up to 0.74 cm2 V–1 s–1, with a common synthetic motif of bulky 2-octyldodecyl side groups on the conjugated backbone. Spectroscopy, diffraction, and microscopy measurements reveal a transition in molecular packing behavior from a preferentially edge-on orientation of the conjugated plane to a preferentially face-on orientation as the attachment density of the side chains increases.
Abstract The synthesis and optimization of new photovoltaic donor polymers is a time-consuming pr... more Abstract The synthesis and optimization of new photovoltaic donor polymers is a time-consuming process. Computer-based molecular simulations can narrow the scope of materials choice to the most promising ones, by identifying materials with desirable energy levels and absorption energies. In this paper, such a retrospective analysis is presented of a series of fused aromatic push–pull copolymers.
Journal of the American Chemical Society, Jan 1, 2012
We study the appearance and energy of the charge transfer (CT) state using measurements of electr... more We study the appearance and energy of the charge transfer (CT) state using measurements of electroluminescence (EL) and photoluminescence (PL) in blend films of high-performance polymers with fullerene acceptors. EL spectroscopy provides a direct probe of the energy of the interfacial states without the need to rely on the LUMO and HOMO energies as estimated in pristine materials. For each polymer, we use different fullerenes with varying LUMO levels as electron acceptors, in order to vary the energy of the CT state relative to the blend with [6,6]-phenyl C61-butyric acid methyl ester (PCBM). As the energy of the CT state emission approaches the absorption onset of the blend component with the smaller optical bandgap, E(opt,min) ≡ min{E(opt,donor); E(opt,acceptor)}, we observe a transition in the EL spectrum from CT emission to singlet emission from the component with the smaller bandgap. The appearance of component singlet emission coincides with reduced photocurrent and fill factor. We conclude that the open circuit voltage V(OC) is limited by the smaller bandgap of the two blend components. From the losses of the studied materials, we derive an empirical limit for the open circuit voltage: V(OC) ≲ E(opt,min)/e - (0.66 ± 0.08)eV.
The prospect of using low cost, high throughput material deposition processes to fabricate organi... more The prospect of using low cost, high throughput material deposition processes to fabricate organic circuitry and solar cells continues to drive research towards improving the performance of the semiconducting materials utilized in these devices. Conjugated aromatic polymers have emerged as a leading candidate semiconductor material class, due to their combination of their amenability to processing and reasonable electrical and optical performance. Challenges remain, however, to further improve the charge carrier mobility of the polymers for transistor applications and the power conversion efficiency for solar cells. This optimization requires a clear understanding of the relationship between molecular structure and both electronic properties and thin film morphology. In this Account, we describe an optimization process for a series of semiconducting polymers based on an electron rich indacenodithiophene aromatic backbone skeleton. We demonstrate the effect of bridging atoms, alkyl chain functionalization, and co-repeating units on the morphology, molecular orbital energy levels, charge carrier mobility, and solar cell efficiencies. This conjugated unit is extremely versatile with a coplanar aromatic ring structure, and the electron density can be manipulated by the choice of bridging group between the rings. The functionality of the bridging group also plays an important role in the polymer solubility, and out of plane aliphatic chains present in both the carbon and silicon bridge promote solubility. This particular polymer conformation, however, typically suppresses long range organization and crystallinity, which had been shown to strongly influence charge transport. In many cases, polymers exhibited both high solubility and excellent charge transport properties, even where there was no observable evidence of polymer crystallinity. The optical bandgap of the polymers can be tuned by the combination of the donating power of the bridging unit and the electron withdrawing nature of co-repeat units, alternating along the polymer backbone. Using strong donors and acceptors, we could shift the absorption into the near infrared.
Chemical communications (Cambridge, England), Jan 1, 2012
A novel thiophene substituted isoindigo and its copolymer with benzothiadiazole have been synthes... more A novel thiophene substituted isoindigo and its copolymer with benzothiadiazole have been synthesized. The polymer with low lying LUMO energy levels exhibits excellent ambipolar behavior in field effect transistors with both hole and electron mobilities recorded over 0.1 cm(2) V(-1) s(-1).
Thieno [3, 4-b] pyrazine-based poly (heteroarylenevinylene) s (PHAVs)(P-1-P-6) by Horner polycond... more Thieno [3, 4-b] pyrazine-based poly (heteroarylenevinylene) s (PHAVs)(P-1-P-6) by Horner polycondensation and cyano-PHAVs (P-7-P-9) by Knoevenagel polycondensation have been synthesized in quantitative yields. The copolymers are characterized by NMR, IR, UV, GPC, and elemental analysis. High molecular weight (M̄ w up to 279 000 g/mol), thermostable, soluble, and film-forming materials were obtained. The absorption spectra of the polymers show two peaks located in the UV and visible region from~ 384 to 650 nm ...
Abstract Novel copolymers consisting of the alternating push–pull comonomers fluorene and thieno ... more Abstract Novel copolymers consisting of the alternating push–pull comonomers fluorene and thieno [3, 4-b] pyrazine/quinoxaline were synthesized by a palladium-catalyzed Suzuki cross-coupling reaction in 60–80% yields. The structure of the deeply colored copolymers was confirmed with 1 H and 13 C NMR. All the new materials were characterized with spectroscopic and electrochemical methods. Bulk heterojunction organic solar cells based on some of the novel polymers in combination with the well-known fullerene acceptor [6, 6 ...
High-performance, solution-processed transistors fabricated from semiconducting polymers containi... more High-performance, solution-processed transistors fabricated from semiconducting polymers containing indacenodithiohene repeat units are described. The bridging functions on the backbone contribute to suppressing large-scale crystallization in thin films. However, charge carrier mobilities of up to 1 cm2/(V s) for a benzothiadiazole copolymer were reported and, coupled with both ambient stability and long-wavelength absorption, make this family of polymers particularly attractive for application in next-generation organic optoelectronics.
Thieno [3, 2-b] thienobis (silolothiophene), a new electron rich hexacyclic monomer has been synt... more Thieno [3, 2-b] thienobis (silolothiophene), a new electron rich hexacyclic monomer has been synthesized and incorporated into three novel donor-acceptor low-bandgap polymers. By 10 carefully choosing the acceptor co-monomer, the energy levels of the polymers could be modulated and high power conversion efficiencies of 5.52% were reached in OPV devices.
Two novel indacenodithiophene (IDT) based donor-acceptor conjugated polymers for use in organic f... more Two novel indacenodithiophene (IDT) based donor-acceptor conjugated polymers for use in organic field effect transistors and photovoltaic devices are synthesized and characterized. The effect of inclusion of two fluorine atoms on the acceptor portion of the polymer is thoroughly investigated via a range of techniques. The inductively withdrawing and mesomerically donating properties of the fluorine atoms result in a decrease of the HOMO, with little effect on the LUMO as demonstrated through DFT analysis.
We describe a series of highly soluble diketo pyrrolo-pyrrole (DPP)-bithiophene copolymers exhibi... more We describe a series of highly soluble diketo pyrrolo-pyrrole (DPP)-bithiophene copolymers exhibiting field effect hole mobilities up to 0.74 cm2 V–1 s–1, with a common synthetic motif of bulky 2-octyldodecyl side groups on the conjugated backbone. Spectroscopy, diffraction, and microscopy measurements reveal a transition in molecular packing behavior from a preferentially edge-on orientation of the conjugated plane to a preferentially face-on orientation as the attachment density of the side chains increases.
Abstract The synthesis and optimization of new photovoltaic donor polymers is a time-consuming pr... more Abstract The synthesis and optimization of new photovoltaic donor polymers is a time-consuming process. Computer-based molecular simulations can narrow the scope of materials choice to the most promising ones, by identifying materials with desirable energy levels and absorption energies. In this paper, such a retrospective analysis is presented of a series of fused aromatic push–pull copolymers.
Journal of the American Chemical Society, Jan 1, 2012
We study the appearance and energy of the charge transfer (CT) state using measurements of electr... more We study the appearance and energy of the charge transfer (CT) state using measurements of electroluminescence (EL) and photoluminescence (PL) in blend films of high-performance polymers with fullerene acceptors. EL spectroscopy provides a direct probe of the energy of the interfacial states without the need to rely on the LUMO and HOMO energies as estimated in pristine materials. For each polymer, we use different fullerenes with varying LUMO levels as electron acceptors, in order to vary the energy of the CT state relative to the blend with [6,6]-phenyl C61-butyric acid methyl ester (PCBM). As the energy of the CT state emission approaches the absorption onset of the blend component with the smaller optical bandgap, E(opt,min) ≡ min{E(opt,donor); E(opt,acceptor)}, we observe a transition in the EL spectrum from CT emission to singlet emission from the component with the smaller bandgap. The appearance of component singlet emission coincides with reduced photocurrent and fill factor. We conclude that the open circuit voltage V(OC) is limited by the smaller bandgap of the two blend components. From the losses of the studied materials, we derive an empirical limit for the open circuit voltage: V(OC) ≲ E(opt,min)/e - (0.66 ± 0.08)eV.
The prospect of using low cost, high throughput material deposition processes to fabricate organi... more The prospect of using low cost, high throughput material deposition processes to fabricate organic circuitry and solar cells continues to drive research towards improving the performance of the semiconducting materials utilized in these devices. Conjugated aromatic polymers have emerged as a leading candidate semiconductor material class, due to their combination of their amenability to processing and reasonable electrical and optical performance. Challenges remain, however, to further improve the charge carrier mobility of the polymers for transistor applications and the power conversion efficiency for solar cells. This optimization requires a clear understanding of the relationship between molecular structure and both electronic properties and thin film morphology. In this Account, we describe an optimization process for a series of semiconducting polymers based on an electron rich indacenodithiophene aromatic backbone skeleton. We demonstrate the effect of bridging atoms, alkyl chain functionalization, and co-repeating units on the morphology, molecular orbital energy levels, charge carrier mobility, and solar cell efficiencies. This conjugated unit is extremely versatile with a coplanar aromatic ring structure, and the electron density can be manipulated by the choice of bridging group between the rings. The functionality of the bridging group also plays an important role in the polymer solubility, and out of plane aliphatic chains present in both the carbon and silicon bridge promote solubility. This particular polymer conformation, however, typically suppresses long range organization and crystallinity, which had been shown to strongly influence charge transport. In many cases, polymers exhibited both high solubility and excellent charge transport properties, even where there was no observable evidence of polymer crystallinity. The optical bandgap of the polymers can be tuned by the combination of the donating power of the bridging unit and the electron withdrawing nature of co-repeat units, alternating along the polymer backbone. Using strong donors and acceptors, we could shift the absorption into the near infrared.
Chemical communications (Cambridge, England), Jan 1, 2012
A novel thiophene substituted isoindigo and its copolymer with benzothiadiazole have been synthes... more A novel thiophene substituted isoindigo and its copolymer with benzothiadiazole have been synthesized. The polymer with low lying LUMO energy levels exhibits excellent ambipolar behavior in field effect transistors with both hole and electron mobilities recorded over 0.1 cm(2) V(-1) s(-1).
Thieno [3, 4-b] pyrazine-based poly (heteroarylenevinylene) s (PHAVs)(P-1-P-6) by Horner polycond... more Thieno [3, 4-b] pyrazine-based poly (heteroarylenevinylene) s (PHAVs)(P-1-P-6) by Horner polycondensation and cyano-PHAVs (P-7-P-9) by Knoevenagel polycondensation have been synthesized in quantitative yields. The copolymers are characterized by NMR, IR, UV, GPC, and elemental analysis. High molecular weight (M̄ w up to 279 000 g/mol), thermostable, soluble, and film-forming materials were obtained. The absorption spectra of the polymers show two peaks located in the UV and visible region from~ 384 to 650 nm ...
Abstract Novel copolymers consisting of the alternating push–pull comonomers fluorene and thieno ... more Abstract Novel copolymers consisting of the alternating push–pull comonomers fluorene and thieno [3, 4-b] pyrazine/quinoxaline were synthesized by a palladium-catalyzed Suzuki cross-coupling reaction in 60–80% yields. The structure of the deeply colored copolymers was confirmed with 1 H and 13 C NMR. All the new materials were characterized with spectroscopic and electrochemical methods. Bulk heterojunction organic solar cells based on some of the novel polymers in combination with the well-known fullerene acceptor [6, 6 ...
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