Polaron Delocalization in Donor-Acceptor Polymers and its Impact on Organic Electrochemical Transist
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Moser, Maximilian↗
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Topology and ground state control in open-shell donor-acceptor conjugated polymers
Donor-acceptor (DA) conjugated polymers (CPs) with narrow bandgaps and open-shell (diradical) character represent an emerging class of materials whose rich behavior emanates from their collective electronic properties and diminished electron pairing. However, the structural and electronic heterogeneities that define these materials complicate bandgap control at low energies and connections linking topology, exchange interactions, and (opto)electronic functionality remain nascent. To address these challenges, we demonstrate structurally rigid and strongly π-conjugated copolymers comprised of a solubilizing thiadiazoloquinoxaline acceptor and cyclopenta[2,1-b:3,4-b']dithiophene or dithieno[3,2-b:2',3'-d]thiophene donors. Atom-specific substitution modulates local aromatic character within the donor resulting in dramatic differences in structural, physicochemical, electronic, and magnetic properties of the polymers. These long-range π-mediated interactions facilitate control between low-spin aromatic and high-spin quinoidal forms. This work provides a strategy to understand the evolution of the electronic structure within DA CPs, control the ground state spin multiplicity, tune spin-spin interactions, and articulate the emergence of their novel properties.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Ground-state electron transfer in all-polymer donor-acceptor heterojunctions
Abstract not provided
Xu, Kai↗
Side chain independent photovoltaic performance of thienopyrroledione conjugated donor-acceptor polymers
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99 GENERAL AND MISCELLANEOUS↗
Dichlorinated Dithienylethene-Based Copolymers for Air-Stable n-Type Conductivity and Thermoelectricity
Here, two donor-acceptor polymers were obtained by coupling difluoro- and dichloro-substituted forms of the electron-deficient unit BDOPV and the relatively weak donor moiety dichlorodithienylethene (ClTVT). The conductivity and power factors of doped devices are different for the chlorinated and fluorinated BDOPV polymers. High electron conductivity of 38.3 and 16.1 S cm -1 were obtained from the chlorinated and fluorinated polymers with N-DMBI, respectively, and 12.4 and 2.4 S cm -1 were obtained from the chlorinated and fluorinated polymers with CoCp 2 , respectively, from drop-cast devices. The corresponding power factors are 22.7, 7.6, 39.5 and 8.0 μW m -1 K -2 , respectively. Doping of PClClTVT with N-DMBI results in excellent air-stability; the electron conductivity of devices with 50 mol% N-DMBI as dopant remained up to 4.9 S m -1 after 222 days in the air, the longest for an n-doped polymer stored in air, with a thermoelectric power factor of 9.3 μW m -1 K -2 . However, the conductivity of PFClTVT-based devices can hardly be measured after 103 days. These observations are consistent with morphologies determined by grazing incidence wide angle X-ray scattering (GIWAXS) and atomic force microscopy (AFM). The results demonstrate that chemical structures leading to dense and ordered packing can enhance electron conductivity and air stability of n-type donor-acceptor polymers.
30 DIRECT ENERGY CONVERSION↗
Highly stretchable organic electrochemical transistors with strain-resistant performance
Realizing fully stretchable electronic materials is central to advancing new types of mechanically agile and skin-integrable optoelectronic device technologies. Here we demonstrate a materials design concept combining an organic semiconductor film with a honeycomb porous structure with biaxially prestretched platform that enables high-performance organic electrochemical transistors with a charge transport stability over 30-140% tensional strain, limited only by metal contact fatigue. In this work, the prestretched honeycomb semiconductor channel of donor-acceptor polymer poly(2,5-bis(2-octyldodecyl)-3,6-di(thiophen-2-yl)-2,5-diketo-pyrrolopyrrole-alt-2,5-bis(3-triethyleneglycoloxy-thiophen-2-yl) exhibits high ion uptake and completely stable electrochemical and mechanical properties over 1,500 redox cycles with 10(4) stretching cycles under 30% strain. Invariant electrocardiogram recording cycles and synapse responses under varying strains, along with mechanical finite element analysis, underscore that the present stretchable organic electrochemical transistor design strategy is suitable for diverse applications requiring stable signal output under deformation with low power dissipation and mechanical robustness. Highly stretchable organic electrochemical transistors with stable charge transport under severe tensional strains are demonstrated using a honeycomb semiconducting polymer morphology, thereby enabling controllable signal output for diverse stretchable bioelectronic applications.
36 MATERIALS SCIENCE↗
Observation of Stepwise Ultrafast Crystallization Kinetics of Donor–Acceptor Conjugated Polymers and Correlation with Field Effect Mobility
The semicrystalline microstructures of donor-acceptor conjugated polymers strongly impact their optoelectronic properties. The control of the microstructure relies on the understandings of the crystallization processes in these polymers, from packing structures to crystallization kinetics. How fast these conjugated polymer chains crystallize and how their chemical structures and pre-existing microstructure history influence their crystallization have so far remained unclear, due to the fast crystallization rate caused by chain rigid structures and strong interactions. Here, ultrafast scanning calorimetry (FSC) is employed to reveal the crystallization behaviors of high perform- ance diketopyrrolopyrrole (DPP)-based conjugated polymers with scanning rates up to 500 000 K/s. Through elaborately designed nonisothermal and isothermal crystallization studies, we probed the fast crystallization kinetics and extracted the two-step crystallization process of these polymers quantitatively. We found that both the rigidity of the chain backbones and the preinduced crystalline microstructures can influence the crystallization rate over an order of magnitude at the same degree of undercooling. We further demonstrated the manipulated crystallization kinetics in the DPP-based polymer films with different amounts of preinduced crystallites and correlate it to the polymers’ charge transport mobility.
36 MATERIALS SCIENCE↗
Electronic properties and optical spectra of donor–acceptor conjugated organic polymers
Organic semiconductors based on conjugated donor-acceptor (D–A) polymers are a unique platform for electronic, spintronic, and energy-harvesting devices. Understanding the electronic structure of D–A polymers with a small band gap is essential for developing next-generation technologies. Here, we investigate the electronic structure and optical spectra of cyclopentadithiophene-based closed/open-shell D–A polymers using density functional theory and the Bethe–Salpeter equation based on G 0 W 0 approximation. We explored the role of different acceptor units and chemical substitutions on the structural changes and, more importantly, electronic, optical, and dielectric behavior. We found that the computed first exciton peak of the polymers agreed well with the available experimentally measured optical gap. Furthermore, D–A polymers with open-shell character display higher dielectric constant than the closed-shell polymers. We show that the exceptional performance of polycyclopentadithiophene-thiophenylthiadiazoloquinoxaline (PCPDT-TTQ) as a scalable n-type material for Faradaic supercapacitors can be partly ascribed to its elevated dielectric constant. Consequently, these D–A polymers, characterized by their high dielectric constants, exhibit significant potential for various applications, including energy storage, organic electronics, and the production of dielectric films.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
From p- to n-Type Mixed Conduction in Isoindigo-Based Polymers through Molecular Design
Organic mixed ionic and electronic conductors are of significant interest for bioelectronic applications. Here, we use three different isoindigoid building blocks to obtain polymeric mixed conductors with vastly different structural and electronic properties which can be further fine-tuned through the choice of comonomer unit. We show how careful design of the isoindigoid scaffold can afford highly planar polymer structures with high degrees of electronic delocalization, while subtle structural modifications can control the dominant charge carrier (hole or electron) when probed in organic electrochemical transistors. We employ a combination of experimental and computational techniques to probe electrochemical, structural and mixed ionic and electronic properties of the polymer series which in turn allows us to derive important structure-property relations for this promising class of materials in the context of organic bioelectronics. Ultimately, we use these findings to outline robust molecular design strategies for isoindigo-based mixed conductors that can support efficient p-type, n-type and ambipolar transistor operation in an aqueous environment.
36 MATERIALS SCIENCE↗
Understanding Solution State Conformation and Aggregate Structure of Conjugated Polymers via Small Angle X-ray Scattering
Donor-acceptor (D-A) conjugated polymers are high-performance organic electronic materials that exhibit complex aggregation behavior. Understanding the solution state conformation and aggregation of conjugated polymers is crucial for controlling morphology during thin-film deposition and the subsequent electronic performance. However, a precise multiscale structure of solution state aggregates is lacking. Here, we present an in-depth small-angle X-ray scattering (SAXS) analysis of the solution state structure of an isoindigo-bithiophene-based D-A polymer (PII-2T) in chlorobenzene and decane as our primary system. Modeling the system as a combination of hierarchical fibrillar aggregates mixed with dispersed polymers, we extract information about conformation and multiscale aggregation and also clarify the physical origin of features often observed but unaddressed or misinterpreted in small-angle scattering patterns of conjugated polymers. The persistence length of the D-A polymer extracted from SAXS agrees well with a theoretical model based on the dihedral potentials. Additionally, we show that the broad high q structure factor peak seen in scattering profiles can be attributed to lamellar stacking occurring within the fibril aggregates and that the low q aggregate scattering is strongly influenced by the polymer molecular weight. Overall, the SAXS profiles of D-A polymers in general exhibit a sensitive dependence on the co-existence of fibrillar aggregate and dispersed polymer chain populations. We corroborate our findings from SAXS with electron microscopy of freeze-dried samples for direct imaging of fibrillar aggregates. Finally, we demonstrate the generality of our approach by fitting the scattering profiles of a variety of D-A polymers based on thieno-isoindigo (PTII-2T), diketopyrrolopyrrole (DPP2T-TT, DPP-BTZ, PDPP2FT-C- 16 ), naphthalenediimide (P(NDI2OD-T2)), and a conjugated block copolymer P3HT-b-DPPT-T. The results presented here establish a picture of the D-A polymer solution state structure and provide a general method of interpreting and analyzing their scattering profiles.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Soft and Stretchable Thienopyrroledione–Based Polymers via Direct Arylation
π-conjugated polymers (CPs) that are concurrently soft and stretchable are needed for deformable electronics. Molecular-level modification of indacenodithiophene (IDT) copolymers, a class of CPs that exhibit high hole mobilities (μ hole ), is an approach that can help realize intrinsically soft and stretchable CPs. Numerous examples of design strategies to adjust the stretchability of CPs exist, but imparting softness is comparatively less studied. In this study, a systematic molecular weight (MW) series is constructed on a promising candidate for soft CPs, poly(indacenodithiophene-co-thienopyrroledione) (p(IDT C16- TPD C8 )), by optimizing direct arylation polymerization conditions in hopes of improving stretchability and μhole without significantly impacting softness. We found p(IDT C16- TPD C8 ) at a degree of polymerization of 32 shows high stretchability (crack onset strain, CoS > 100%) without significantly impacting softness (elastic modulus, E = 32 MPa), which to the best of our knowledge outperforms previously reported stretchable and soft CPs. To further study how molecular-level modifications impact polymer properties, a MW series of a new extended donor unit polymer, poly(indacenodithienothiophene-co-thienopyrroledione) (p(IDTT C16- TPD C8 )), was synthesized. The IDTT C16 copolymers did not result in a greater average μ hole when comparing between p(IDTT C16- TPD C8 ) and p(IDT C16- TPD C8 ) despite their higher crystallinity observed by GIWAXS. While these findings warrant further investigation, this study points toward unique charge transport properties of IDT-based polymers.
direct arylation polymerization↗
Dispersions of Carbon nanotubes in Polymer Matrices
Dispersions of carbon nanotubes exhibiting long term stability are based on a polymer matrix having moieties therein which are capable of a donor-acceptor complexation with carbon nanotubes. The carbon nanotubes are introduced into the polymer matrix and separated therein by standard means. Nanocomposites produced from these dispersions are useful in the fabrication of structures, e.g., lightweight aerospace structures.
Wise, Kristopher Eric↗
Unravelling the Role of Electron Acceptors for the Universal Enhancement of Charge Transport in Quinoid-Donor-Acceptor Polymers for High-Performance Transistors
The quinoid-donor-acceptor (Q-D-A) strategy has recently emerged as a promising approach for constructing high mobility semiconducting polymers. In order to fully explore the potential of this strategy in improving the charge transport and elucidating the structure-property-performance relationships in Q-D-A polymers, a series of new polymers with different electron acceptor units and backbone coplanarity have been synthesized and characterized. In this work, all of the resulting Q-D-A polymers exhibit much more planar backbone conformations in comparison to their donor-acceptor (D-A) counterparts. Moreover, organic field-effect transistors based on Q-D-A polymers exhibit excellent effective hole mobilities in a range of 0.44 to 3.35 cm 2 V –1 s –1 , most of which are orders of magnitude higher than those of their corresponding D-A polymers. Notably, the hole mobility of 3.35 cm 2 V –1 s –1 is among the highest for the quinoidal-aromatic polymers characterized by conventional spin-coating methods. Furthermore, the role of electron acceptors in Q-D-A polymers has been comprehensively investigated. Polymers with stronger acceptor units are more inclined to deliver edge-on lamellas, high film crystallinity, small effective hole masses, and decent operational stability. The detailed structure-property-device performance relationship will pave the way toward high performance semiconducting polymers using the potent Q-D-A strategy.
36 MATERIALS SCIENCE↗
Sulfur Conversion to Donor‐Acceptor Ladder Polymer Networks through Mechanochemical Nucleophilic Aromatic Substitution for Efficient CO 2 Photoreduction
The development of synthetic methods capable of converting elemental sulfur into conjugated porous sulfur‐rich polymers remains a great challenge, although direct utilization of this readily available feedstock can significantly enrich its uses and circumvent environmental problems during sulfur storage. Here, we report herein mechanochemical (MC) nucleophilic aromatic substitution (S N Ar) that enables sulfur conversion into thianthrene‐bridged porous ladder polymer networks with dense donor‐acceptor (D−A) molecular junctions. We demonstrate that the key lies in the generation of bent thianthrene units through a solid‐state ball‐milling condensation reaction between 1,2‐dihaloarenes and elemental sulfur. We also show that the assembling of D−A structural motifs into porous networks affords efficient visible‐light‐driven photocatalytic reduction of carbon dioxide (CO 2 ) with water (H 2 O) vapor, in the absence of any additional photosensitizer, sacrificial agents or cocatalysts. Exceptional photoinduced charge separation along with boosted exciton dissociation results in a high‐performance of carbon monoxide (CO) production rate of 306.1 μmol g −1 h −1 with near 100 % CO selectivity, which is accompanied by H 2 O oxidation to O 2 , as confirmed by both experimental and theoretical results. We anticipate this novel MC S N Ar approach will advance processing techniques for direct sulfur utilization and facilitate new possibilities for the synthesis of D−A ladder polymer networks with promising potential in photocatalysis.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
All-polymer organic solar cells with nano-to-micron hierarchical morphology and large light receiving angle
Distributed photovoltaics in living environment harvest the sunlight in different incident angles throughout the day. The development of planer solar cells with large light-receiving angle can reduce the requirements in installation form factor and is therefore urgently required. Here, thin film organic photovoltaics with nano-sized phase separation integrated in micro-sized surface topology is demonstrated as an ideal solution to proposed applications. All-polymer solar cells, by means of a newly developed sequential processing, show large magnitude hierarchical morphology with facilitated exciton-to-carrier conversion. The nano fibrilar donor-acceptor network and micron-scale optical field trapping structure in combination contributes to an efficiency of 19.06% (certified 18.59%), which is the highest value to date for all-polymer solar cells. Furthermore, the micron-sized surface topology also contributes to a large light-receiving angle. A 30% improvement of power gain is achieved for the hierarchical morphology comparing to the flat-morphology devices. These inspiring results show that all-polymer solar cell with hierarchical features are particularly suitable for the commercial applications of distributed photovoltaics due to its low installation requirement.
14 SOLAR ENERGY↗
Donor–Acceptor Conjugated Copolymers Containing Transition-Metal Complex: Intrachain Magnetic Exchange Interactions and Magneto-Optical Activity
A donor-acceptor conjugated copolymer containing thienothiophene (TT) (Donor) units and Co(II) complexes (Acceptor) has been synthesized and characterized. The studies of magnetic properties of the polymers by SQUID and EPR measurements showed antiferromagnetic exchange interaction between neighboring spin centers along with the polymer backbone through intrachain in-teractions. It is the first time that D-A conjugated polymer backbone serving as bridging ligands for magnetic couplings, making this type of polymers promising as magnetic materials. Moreover, the magneto-optical activity (MOA) of polymer LCP1 was char-acterized using magnetic circular dichroism (MCD) spectroscopy. It was found that the material exhibits a large magneto-optic rotation with a peak Verdet constant of 2980 deg*T -1 *m -1 at 590 nm.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Second and third order nonlinear optical properties of conjugated molecules and polymers
Second- and third-order nonlinear optical properties of some newly synthesized organic molecules and polymers are reported. Powder second-harmonic-generation efficiencies of up to 200 times urea have been realized for asymmetric donor-acceptor acetylenes. Third harmonic generation chi(3)s have been determined for a series of small conjugated molecules in solution. THG chi(3)s have also been determined for a series of soluble conjugated copolymers prepared using ring-opening metathesis polymerization. The results are discussed in terms of relevant molecular and/or macroscopic structural features of these conjugated organic materials.
Perry, Joseph W.↗
Revealing aggregation of non-fullerene acceptors in intermixed phase by ultraviolet-visible absorption spectroscopy
Non-fullerene acceptor (NFA) aggregation is crucial in determining bulk-heterojunction (BHJ) organic photovoltaic (OPV) performance. However, it is still a big challenge to characterize the nanostructure of NFAs in the disordered donor-acceptor intermixed phase. Here, we demonstrate a method to characterize NFA aggregation and composition in the intermixed phase by measuring NFA concentration-dependent ultraviolet-visible (UV-vis) absorption spectroscopy of BHJ films. In various polymer:NFA films, an absorption shift as a function of increasing molecular concentration (ASIMC) phenomenon is observed, and different NFA aggregation behaviors can be distinguished. The ASIMC method was then applied to study the influence of processing conditions on the NFA concentration in the intermixed phase of devices to establish a correlation with device efficiency. The current work provides a feasible tool to study the nanostructure of NFAs in the complex polymer matrix and to understand the variations in the NFA concentration in the intermixed phase under non-equilibrium conditions.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗