Rational Design of Donor Acceptor Based Semiconducting Copolymers with High Dielectric Constant

<div> <div> <div> <p>An efficient photogeneration of free charge carriers has long been recognized as the paramount challenge in organic photovoltaic (OPV) devices. The low dielectric constant organic semiconductors fall short to reduce strong Coulombic interaction of tightly bound exciton and hence lead to a loss mechanism in OPVs due to charge-carrier recombination. To circumvent this problem, we adopt a strategy to enhance the dielectric constant of organic semiconductors by incorporating tetraethyleneglycol (TEG) side-chains. We report synthesis of three new semiconducting copolymers by combining thiophene substituted diketopyrrolopyrrole (TDPP) monomer with three other monomeric units with varying electron donating strength: benzodithiophene (BBT-3TEG-TDPP), TDPP (TDPP-3TEG-TDPP) and naphthalene diimide (PNDITEG-TDPP). BBT-3TEG-TDPP and PNDITEG-TDPP showed highest dielectric constants (~ 5) at 1MHz frequency suggesting efficient contribution of dipolar polarization from TEG side-chains. To understand the electronic contribution of the polymer backbone and the polarity of TEG side-chains, and the resulting enhancement of the dielectric constant, we further performed first-principles density functional theory calculations. Single-component organic solar cells (OSC) fabricated utilizing these polymers resulted in poor performance which is attributed to the absence of free charge generation. Furthermore, transient absorption spectroscopy studies show low exciton diffusion length as observed in donor-acceptor type conjugated polymers. Our results suggest that, the strategy of enhancing dielectric constant with polar side-chains is not sufficient to reduce Coulombic interaction between hole and electron in OSCs. </p> </div> </div> </div>

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An effective strategy to enhance the dielectric constant of organic semiconductors – CPDTTPD-based low bandgap polymers bearing oligo(ethylene glycol) side chains

Journal of Materials Chemistry C ◽

10.1039/c7tc05264b ◽

2018 ◽

Vol 6 (3) ◽

pp. 500-511 ◽

Cited By ~ 16

Author(s):

Jeroen Brebels ◽

Evgenia Douvogianni ◽

Dries Devisscher ◽

Raghavendran Thiruvallur Eachambadi ◽

Jean Manca ◽

...

Keyword(s):

Dielectric Constant ◽

Ethylene Glycol ◽

Organic Semiconductors ◽

Dielectric Constants ◽

Side Chains ◽

Effective Strategy ◽

Low Bandgap

Gradually increasing dielectric constants (up to 6.3) are obtained for a series of PCPDTTPD polymers.

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Photoconversion Mechanism at the pn-Homojunction Interface in Single Organic Semiconductor

Materials ◽

10.3390/ma13071727 ◽

2020 ◽

Vol 13 (7) ◽

pp. 1727 ◽

Cited By ~ 1

Author(s):

Ji-Hyun Lee ◽

Armand Perrot ◽

Masahiro Hiramoto ◽

Seiichiro Izawa

Keyword(s):

Organic Semiconductors ◽

Organic Semiconductor ◽

Energy Structure ◽

Free Charge ◽

Charge Generation ◽

Recombination Processes ◽

Single Host ◽

Donor Acceptor ◽

Doping Technique ◽

Determining Factor

Clarifying critical differences in free charge generation and recombination processes between inorganic and organic semiconductors is important for developing efficient organic photoconversion devices such as solar cells (SCs) and photodetector. In this study, we analyzed the dependence of doping concentration on the photoconversion process at the organic pn-homojunction interface in a single organic semiconductor using the temperature dependence of J–V characteristics and energy structure measurements. Even though the organic pn-homojunction SC devices were fabricated using a single host material and the doping technique resembling an inorganic pn-homojunction, the charge generation and recombination mechanisms are similar to that of conventional donor/acceptor (D/A) type organic SCs; that is, the charge separation happens from localized exciton and charge transfer (CT) state being separated by the energy offset between adjacent molecules, and the recombination happens from localized charge carrier at two adjacent molecules. The determining factor for photoconversion processes is the localized nature of charges in organic semiconductors. The results demonstrated that controlling the delocalization of the charges is important to realize efficient organic photoconversion devices.

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Pulsed Laser Deposition of BaxSr1−xTiO3 Films on MgO, LaAlO3 and SrTiO3 for Tunable Microwave Applications

MRS Proceedings ◽

10.1557/proc-541-693 ◽

1998 ◽

Vol 541 ◽

Cited By ~ 5

Author(s):

Wontae Chang ◽

James S. Horwitz ◽

Won-Jeong Kim ◽

Jeffrey M. Pond ◽

Steven W. Kirchoefer ◽

...

Keyword(s):

Dielectric Constant ◽

Dielectric Properties ◽

Electric Field ◽

Pulsed Laser Deposition ◽

Pulsed Laser ◽

Dielectric Constants ◽

Laser Deposition ◽

Film Stress ◽

Donor Acceptor ◽

Bst Films

AbstractSingle phase BaxSr1−xTiO3 (BST) films (∼0.5-7 μm thick) have been deposited onto single crystal substrates (MgO, LaAlO3, SrTiO3) by pulsed laser deposition. Silver interdigitated electrodes were deposited on top of the ferroelectric film. The room temperature capacitance and dielectric Q (1/tanδ) of the film have been measured as a function of electric field (≤80 kV/cm) at 1 - 20 GHz. The dielectric properties of the film are observed to strongly depend on substrate type and post-deposition processing. After annealing (≤1000° C), it was observed that the dielectric constant and % tuning decreased and the dielectric Q increased for films deposited onto MgO, and the opposite effect was observed for films deposited onto LaA1O3. Presumably, this change in dielectric properties is due to the changes in film stress. Very thin (∼50 Å) amorphous BST films were successfully used as a stress-relief layer for the subsequently deposited crystalline BST (∼5000 Å) films to maximize % tuning and dielectric Q. Films have been deposited from stoichiometric targets and targets that have excess Ba and Sr. The additional Ba and Sr has been added to the target to compensate for deficiencies in Ba and Sr observed in the deposited BST (x=0.5) films. Films deposited from compensated targets have higher dielectric constants than films deposited from stoichiometric targets. Donor/acceptor dopants have also been added to the BST target (Mn, W, Fe ≤4 mol.%) to further improve the dielectric properties. The relationship between the dielectric constant, the dielectric Q, the change in dielectric constant with electric field is discussed.

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Comparative Experimental and Theoretical Study of Mg, Al and Zn Aryloxy Complexes in Copolymerization of Cyclic Esters: The Role of the Metal Coordination in Formation of Random Copolymers

Polymers ◽

10.3390/polym12102273 ◽

2020 ◽

Vol 12 (10) ◽

pp. 2273

Author(s):

Ilya Nifant’ev ◽

Pavel Komarov ◽

Valeriya Ovchinnikova ◽

Artem Kiselev ◽

Mikhail Minyaev ◽

...

Keyword(s):

Density Functional ◽

Rational Design ◽

Qualitative Difference ◽

Random Copolymers ◽

Coordination Polymerization ◽

Polymer Backbone ◽

Catalytic Behavior ◽

Cyclic Esters ◽

Dft Modeling ◽

The Density Functional Theory

Homogeneity of copolymers is a general problem of catalytic coordination polymerization. In ring-opening polymerization of cyclic esters, the rational design of the catalyst is generally applied to solve this problem by the equalization of the reactivities of comonomers—however, it often leads to a reduction of catalytic activity. In the present paper, we studied the catalytic behavior of BnOH-activated complexes (BHT)Mg(THF)2nBu (1), (BHT)2AlMe (2) and [(BHT)ZnEt]2 (3), based on 2,6-di-tert-butyl-4-methylphenol (BHT-H) in homo- and copolymerization of L-lactide (lLA) and ε-caprolactone (εCL). Even at 1:5 lLA/εCL ratio Mg complex 1 catalyzed homopolymerization of lLA without involving εCL to the formation of the polymer backbone. On the contrary, Zn complex 3 efficiently catalyzed random lLA/εCL copolymerization; the presence of mono-lactate subunits in the copolymer chain clearly pointed to the transesterification mechanism of copolymer formation. Both epimerization and transesterification side processes were analyzed using the density functional theory (DFT) modeling that confirmed the qualitative difference in catalytic behavior of 1 and 3: Mg and Zn complexes demonstrated different types of preferable coordination on the PLA chain (k2 and k3, respectively) with the result that complex 3 catalyzed controlled εCL ROP/PLA transesterification, providing the formation of lLA/εCL copolymers that contain mono-lactate fragments separated by short oligo(εCL) chains. The best results in the synthesis of random lLA/εCL copolymers were obtained during experiments on transesterification of commercially available PLLA, the applicability of 3/BnOH catalyst in the synthesis of random copolymers of εCL with methyl glycolide, ethyl ethylene phosphonate and ethyl ethylene phosphate was also demonstrated.

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Free Charge Photogeneration in a Single Component High Photovoltaic Efficiency Organic Semiconductor

10.21203/rs.3.rs-376343/v1 ◽

2021 ◽

Author(s):

Justin Hodgkiss ◽

Michael Price ◽

Paul Hume ◽

Aleksandra Ilina ◽

Isabella Wagner ◽

...

Keyword(s):

Organic Semiconductors ◽

Organic Photovoltaics ◽

Photovoltaic Cells ◽

Single Component ◽

Dielectric Constants ◽

Organic Photovoltaic ◽

Free Charge ◽

Photovoltaic Devices ◽

Organic Photovoltaic Devices ◽

Charge Generation

Abstract Organic photovoltaic cells promise cheap, flexible and scalable solar energy. Whereas light directly generates free charges in silicon photovoltaic cells, bound electron and hole pairs known as excitons are understood to be the primary excitations in organic semiconductors due to their low dielectric constants. These excitons must then be split apart at molecular heterojunctions in order to extract current. Recent record efficiency organic photovoltaics utilise the small molecule, Y6, as a key component in the photon-absorbing blend layer. This molecule and its analogues – unlike previous organic semiconductors – have both low band-gaps and high dielectric constants. Here we show that, in a neat film of Y6, these factors lead to intrinsic free charge generation without the need for a molecular heterojunction to split the exciton. We use a suite of intensity-dependent optical spectroscopy measurements to show that a significant (20-90%) fraction of free charges exist in equilibrium with bound states at light intensity equivalent to 1 sun. Rapid bimolecular charge recombination constrains single component Y6 organic photovoltaic devices to low efficiencies, but this recombination is reduced by the introduction of small quantities of donor polymer. Quantum-chemical calculations reveal charge generation pathways through strong coupling between exciton and CT states, and an intermolecular polarisation pattern that drives exciton dissociation. Our results challenge the understanding of how current record efficiency organic photovoltaics operate, and point towards new future possibilities – offering a molecular picture of intrinsic charge generation as a platform to improve charge yields, and renewing the possibility of efficient single-component organic photovoltaic devices.

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Structure and Doping Optimization of IDT-Based Copolymers for Thermoelectrics

Polymers ◽

10.3390/polym12071463 ◽

2020 ◽

Vol 12 (7) ◽

pp. 1463

Author(s):

Tongchao Liu ◽

Dexun Xie ◽

Jinjia Xu ◽

Chengjun Pan

Keyword(s):

Organic Semiconductors ◽

Carrier Mobility ◽

Carrier Transport ◽

Room Temperature ◽

Charge Carrier Transport ◽

Structure Property ◽

Polymer Backbone ◽

Donor Acceptor ◽

Higher Carrier Mobility ◽

The Relationship

π-conjugated backbones play a fundamental role in determining the thermoelectric (TE) properties of organic semiconductors. Understanding the relationship between the structure–property–function can help us screen valuable materials. In this study, we designed and synthesized a series of conjugated copolymers (P1, P2, and P3) based on an indacenodithiophene (IDT) building block. A copolymer (P3) with an alternating donor–acceptor (D-A) structure exhibits a narrower band gap and higher carrier mobility, which may be due to the D-A structure that helps reduce the charge carrier transport obstacles. In the end, its power factor reaches 4.91 μW m−1 K−2 at room temperature after doping, which is superior to those of non-D-A IDT-based copolymers (P1 and P2). These results indicate that moderate adjustment of the polymer backbone is an effective way to improve the TE properties of copolymers.

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Resolving Donor–Acceptor Interfaces and Charge Carrier Energy Levels of Organic Semiconductors with Polar Side Chains

Advanced Functional Materials ◽

10.1002/adfm.202004799 ◽

2020 ◽

Vol 30 (46) ◽

pp. 2004799 ◽

Cited By ~ 3

Author(s):

Riccardo Alessandri ◽

Selim Sami ◽

Jonathan Barnoud ◽

Alex H. Vries ◽

Siewert J. Marrink ◽

...

Keyword(s):

Charge Carrier ◽

Organic Semiconductors ◽

Energy Levels ◽

Side Chains ◽

Carrier Energy ◽

Donor Acceptor

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Synthesis and Characterization of Azobenzene-Containing Polydiacetylene Polymers

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.976.46 ◽

2014 ◽

Vol 976 ◽

pp. 46-51

Author(s):

Esthela Albarrán Preza ◽

Enrique Vigueras-Santiago ◽

Susana Hernández López

Keyword(s):

Dielectric Constant ◽

Room Temperature ◽

Main Chain ◽

Dielectric Constants ◽

Electronic Density ◽

Polar Species ◽

Acceptor Group ◽

Covalently Bonded ◽

Donor Acceptor

Polydiacetylenes are a type of highly conjugated polymers, and highly polar species are obtained when these polymers contain donor-acceptor azobenzene entities. In this paper the synthesis, characterization and evaluation of the dielectric constant of two polydiacetylenes containing azobenzenes as pendant groups are discussed. The Azobenzene chromophores are covalently bonded to the main chain, and their polarity is defined by an electro-donor (amine) and an electro-acceptor group (nitro or chlorine) bonded to the ends of a conjugated azobenzene structure. Both polymers were processed into plates of 1cm diameter x 0.674 mm thickness using a thermo mechanic technique. Their dielectric constants were evaluated respect to the temperature in a range of frequency of 110 MHz-1.32 GHz, from room temperature to close to their respective Tg. The dielectric constant for the polymer containing the nitro group was higher than it for polymer containing the chloride atom at all temperatures. It is discussed in terms of the ability to nitro and chloride to attract electronic density.

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