Siloxane-terminated Side Chains Research Articles

All-Polymer Solar Cells Based on a Conjugated Polymer Containing Siloxane-Functionalized Side Chains with Efficiency over 10.

A novel wide-bandgap conjugated copolymer based on an imide-functionalized benzotriazole building block containing a siloxane-terminated side-chain is developed. This copolymer is successfully used to fabricate highly efficient all-polymer solar cells (all-PSCs) processed at room temperature with the green-solvent 2-methyl-tetrahydrofuran. When paired with a naphthalene diimide-based polymer electron-acceptor, the all-PSC exhibits a maximum power conversion efficiency (PCE) of 10.1%, which is the highest value so far reported for an all-PSC. Of particular interest is that the PCE remains 9.4% after thermal annealing at 80 °C for 24 h. The resulting high efficiency is attributed to a combination of high and balanced bulky charge carrier mobility, favorable face-on orientation, and high crystallinity. These observations indicate that the resulting copolymer can be a promising candidate toward high-performance all-PSCs for practical applications.

Complementary Semiconducting Polymer Blends: Influence of Side Chains of Matrix Polymers

The concept of complementary semiconducting polymer blends (c-SPBs) has been recently proposed to achieve enhanced solution processability and/or melt-processing capability for organic electronics. In the previous study, we demonstrated the impact of conjugation-break spacers of matrix polymers. In the current work, we explore the influence of the side chains of the matrix polymer on the physical properties of the pure polymers and their corresponding c-SPBs, including electrical properties and phase transition behaviors. Six diketopyrrolopyrrole (DPP)-based polymers with pentamethylene conjugation-break spacers (CBSs) and various side chains, including branched-alkyl, triethylene glycol (TEG), and siloxane-terminated side chains, were synthesized and characterized. The UV–vis spectra show that the side chains have a noticeable impact on the intermolecular interactions in the solid states. In addition, side chains also have a significant influence on the thermal behaviors of the polymers. Polymers with as...

Benzotriazole-based donor-acceptor type low band gap polymers with a siloxane-terminated side-chain for electrochromic applications

A series of donor–acceptor (D-A) type polymers (P1-P4) bearing a benzotriazole group with a siloxane terminated side-chain and a long alkyl chain were synthesized via Stille coupling, and the electrochromic (EC) properties were characterized by various analytical techniques. The incorporation of hybrid siloxane-solubilizing groups in P1 and P2 influenced the intermolecular interactions among the adjacent polymer chains and increased the solubility of the resulting polymers in common organic solvents. The EC behavior of the polymers revealed a color transition from red to blue upon oxidation and reduction. In particular, P1, containing a short siloxane-terminated side-chain, showed superior optical performances, with transmittance change of 42.7%, the change in optical density of 0.767, and coloration efficiency of up to 327 cm2/C, and exhibited superior operational stability, with little transmittance changes after 100 potential steps. Overall, these properties highlight the potential applications of current polymers in displays and smart windows.

Semi-crystalline photovoltaic polymers with siloxane-terminated hybrid side-chains

Three types of semi-crystalline photovoltaic polymers were synthesized by incorporating a siloxane-terminated organic/inorganic hybrid side-chain and changing the number of fluorine substituents. A branch point away from a polymer main backbone in the siloxane-containing side-chains and the intra- and/or interchain noncovalent coulombic interactions enhance a chain planarity and facile interchain organization. The resulting polymers formed strongly agglomerated films with high roughness, suggesting strong intermolecular interactions. The optical band gap of ca. 1.7 eV was measured for all polymers with a pronounced shoulder peak due to tight π-π stacking. With increasing the fluorine substituents, the frontier energy levels decreased and preferential face-on orientation was observed. The siloxane-terminated side-chains and fluorine substitution promoted the intermolecular packing, showing well resolved lamellar scatterings up to (300) for this series of polymers in the grazing incidence wide angle X-ray scattering measurements. The PPsiDTBT, PPsiDTFBT and PPsiDT2FBT devices showed a power conversion efficiency of 3.16%, 4.40% and 5.65%, respectively, by blending with PC71BM. Langevin-type bimolecular charge recombination was similar for three polymeric solar cells. The main loss in the photocurrent generation for PPsiDTBT:PC71BM was interpreted to originate from the trap assisted charge recombination by measuring light-intensity dependent short-circuit current density ( J sc) and open-circuit voltage ( V oc). Our results provide a new insight into the rational selection of solubilizing substituents for optimizing crystalline interchain packing with appropriate miscibility with PC71BM for further optimizing polymer solar cells.

Low band gap conjugated polymers combining siloxane-terminated side chains and alkyl side chains: side-chain engineering achieving a large active layer processing window for PCE > 10% in polymer solar cells

Side-chain random copolymers show high 3-D hole transport and offer excellent active layer thickness tolerance.

Conjugated Donor–Acceptor Polymers Entailing Pechmann Dye-Derived Acceptor with Siloxane-Terminated Side Chains Exhibiting Balanced Ambipolar Semiconducting Behavior

We present four conjugated donor–acceptor (D–A) polymers PBPDT-Si, PBPDSe-Si, PBPDT, and PBPDSe entailing a new electron acceptor Pechmann dye framework, i.e., bipyrrolylidene-2,2′(1H,1′H)-dione (BPD), and thiophene and selenophene as the respective electron donors. PBPDT-Si and PBPDSe-Si contain siloxane-terminated side chains, while PBPDT and PBPDSe bear branching alkyl chains. The respective HOMO energies of PBPDT-Si and PBPDSe-Si are slightly higher than those of PBPDT and PBPDSe, whereas the respective LUMO energies of PBPDT-Si and PBPDSe-Si are slightly lower than those of PBPDT and PBPDSe. The results reveal that (i) thin films of all four polymers show ambipolar semiconducting performances under a nitrogen atmosphere, (ii) hole and electron mobilities are more balanced for PBPDT-Si and PBPDSe-Si, and (iii) the employment of siloxane-terminated side chains is beneficial for improving charge transporting compared to branching alkyl side chains. Thin film hole and electron mobilities of PBPDT-Si can ...

Diketopyrrolopyrrole-Based Low-Bandgap Conjugated Polymers with Siloxane Side Chains for Electrochromic Applications

A series of conjugated copolymers P1–P3 were synthesized from 3,6-bis(5-bromothiophen-2-yl)-2,5-bis(6-(1,1,1,3,5,5,5-heptamethyltrisiloxan-3-yl)hexyl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione and 2,5-bis(trimethylstannyl)-3,4-dialkoxythiophene or its analogue via Stille coupling reactions, with molecular weights in the range of 13000–18000 g mol–1 and polydispersity indexes of 1.4–1.7. This new type of donor–acceptor polymers demonstrated reasonable switching speed, promising redox stability, together with high optical contrast and coloration efficiency. Although, at the current stage, the hybrid siloxane-terminated side chain did not significantly improve the overall performance of the resultant polymers, the unique chemical properties of the siloxane group would offer possibilities for crosslink after suitable post-polymerization treatment, and thus pave the way for future fine-tuning of the morphology of electrochromic films.

Tuning ‘de Vries-like’ properties in siloxane- and carbosilane-terminated smectic liquid crystals

Smectic liquid crystals with ‘de Vries-like’ properties are characterized by a maximum layer contraction of ≤1% upon transition from the non-tilted SmA phase to the tilted SmC phase. To expand the current library of ‘de Vries-like’ liquid crystals, we have developed a rational design strategy based on a concept of frustration between two structural elements, one promoting the formation of a SmA phase (chloro-terminated side-chain) and another promoting the formation of a SmC phase (siloxane-terminated side-chain). In this paper, we show that one can tune this apparent frustration—and further improve de Vries-like properties—by substituting the 2-phenylpyrimidine core in our first-generation siloxane-terminated mesogens with one of three cores known to be stronger SmC-promoting elements: 6-phenylpyridazine, 2-phenylpyridine and 2-phenylthiadiazole. We also address a fundamental design flaw of siloxane-terminated mesogens, i.e., the hydrolytic instability of siloxane oligomers, by substituting the siloxane end-group with a chemically inert carbosilane end-group. As a result of this study, we found a carbosilane-terminated 2-phenylthiadiazole mesogen that forms a SmC phase at room temperature with de Vries-like properties that are comparable to those of bona fide de Vries-like liquid crystals.