It is reported on the allocation effects of branched alkyl chains, when used as solubility and ordering enhancers of the conjugated donor–accepter (D–A) copolymer backbones, on the ordering and π–π overlapping of the copolymers, that drastically affect the electrical properties of organic field-effect transistors (OFETs). Triisopropylsilylethynyl-benzo[1,2-b:4,5-b′]dithiophene (TIPSBDT) and diketopyrrolopyrrole (DPP)-based copolymers, which have two linear alkyl spacers (methylene (C1) or butylene (C4)) between the DPP and side-substituent (C10H21)CH(C8H17), are synthesized by Suzuki cross-coupling. These copolymer films are spun cast onto a polymer-treated SiO2 dielectric surface, and some are further thermally annealed. The longer spacer, C4, is found to efficiently enhance the coplanarity and conjugation of the D–A backbone, while the C1 does not. The resulting C4-bridged TIPSBDT-DPP-based copolymer readily develops a superior π-extended layer on the dielectric surface; the edge-on chains with randomly oriented side chains can be closely packed with a short π-planar distance (d(010)) of 3.57 Å. Its properties are superior to those of the short spacer C1 system with d(010) ≈3.93 Å. The C4-bridged TIPSBDT-DPP copolymer films yield a field-effect mobility up to 1.2 cm2 V−1 s−1 in OFETs, 12 times as higher than that of the C1 spacer system.
Semiconducting polymers consisting of (E)-1,2-di(thiophen-2-yl)ethene (TVT) derivatives and benzo[1,2-b:4,5-b′]dithiophene with conjugated thiophene side chains (BDTT) were designed and synthesized to investigate the effect of fluorine and cyano groups in the 3-position of the thiophene ring in TVT on the photovoltaic properties. The corresponding PBDTT-TVT, PBDTT-FTVT, and PBDTT-CNTVT copolymers containing TVT, difluoro TVT (FTVT), and dicyano TVT (CNTVT), respectively, demonstrated considerable variations in optical, electrochemical, morphological, and charge transporting properties. PBDTT-FTVT showed suitable frontier orbital energy levels, favorable face-on orientation, and a well-mixed and smooth morphology in the blends with 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2′,3′-d′]-s-indaceno[1,2-b:5,6-b′]dithiophene (ITIC) and [6,6]-phenyl-C71-butyric acid methyl ester (PCBM). In contrast, PBDTT-CNTVT showed unfavorable frontier orbital energy levels and bimodal orientation in the thin-film state, which interrupted efficient charge transport in organic photovoltaic devices. The device fabricated using PBDTT-FTVT exhibited the highest power conversion efficiency (PCE) of up to 6.50% with ITIC and a slightly lower PCE of 6.35% with PCBM.
A series of narrow-band gap, π-conjugated small molecules based on diketopyrrolopyrrole (DPP) electron acceptor units coupled with alkylthienyl-substituted-benzodithiophene (BDTT) electron donors were designed and synthesized for use as donor materials in solution-processed organic photovoltaic cells. In particular, by end-group functionalization of the small molecules with fluorine derivatives, the nanoscale morphologies of the photoactive layers of the photovoltaic cells were successfully controlled. The influences of different fluorine-based end-groups on the optoelectronic and morphological properties, carrier mobilities, and the photovoltaic performances of these materials were investigated. A high power conversion efficiency (PCE) of 6.00% under simulated solar light (AM 1.5G) illumination has been achieved for organic photovoltaic cells based on a small-molecule bulk heterojunction system consisting of a trifluoromethylbenzene (CF3) end-group-containing oligomer (BDTT-(DPP)2-CF3) as the donor and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) as the acceptor. As a result, the introduction of CF3 end-groups has been found to enhance both the short circuit current density (JSC) and fill factor (FF). A tandem photovoltaic device comprising an inverted BDTT-(DPP)2-CF3:PC71BM cell and a poly(3-hexylthiophene) (P3HT):indene-C60-bisadduct (IC60BA)-based cell as the top and bottom cell components, respectively, showed a maximum PCE of 8.30%. These results provide valuable guidelines for the rational design of conjugated small molecules for applications in high-performance organic photovoltaic cells. Furthermore, to the best of our knowledge, this is the first report on the design of fluorine-functionalized BDTT-DPP-based small molecules, which have been shown to be a viable candidate for use in inverted tandem cells.
We have synthesized a new polymeric host material for phosphorescent dyes, which can be used in phosphorescent light-emitting layers. An alternating copolymer, composed of N-alkylcarbazole and tetramethylbenzene units was synthesized through the Suzuki coupling reaction. We fabricated electro-phosphorescent devices using the synthesized polymeric host doped with solution-processible green and red phosphorescent dyes. Light-emitting devices have an ITO/PEDOT/polymer + dopant/Balq3/Alq3/LiF/Al configuration. The device containing one of two studied green dopants (designated as green 1) in the polymeric host showed the best performance, with a maximum luminous efficiency of 29 cd/A. A thin film of this polymeric was successfully patterned by laser-induced thermal imaging (LITI), and an electro-phosphorescent device was fabricated using the patterned film. This patterned device showed performance characteristics similar to those of a spin-coated device.
Although considerable progress has been made in anticounterfeiting film technologies, developing difficult-to-imitate novel anticounterfeiting films is still challenging. Herein, we report novel photopatternable one-dimensional photonic crystal (1D PC)-based anticounterfeiting films, whose colors can be changed by human breath and which can be encrypted and decrypted using small aldehydes and hydrochloric acid, respectively. A photo-crosslinkable TiO2–copolymer hybrid (Ti70) and primary-amine-containing copolymer (P(AEMA97-co-BPA3)–NH2) were prepared and utilized to fabricate 11-layered 1D PC (TiNH2 PC). In addition, using UV post-treatment with customized photomasks, TiNH2 PCs with hidden photopatterns that showed tunable humidity-responsive bright color contrast could be fabricated. However, after exposure to aldehydes, the TiNH2 PC showed reduced or no color shifts in response to further changes in the relative humidity. This is because the hydrophilicity of the P(AEMA97-co-BPA3)–NH2 layers decreased when they converted to P(AEMA97-co-BPA3)-imine layers under aldehyde exposure. However, the aldehyde-exposed TiNH2 PC could be reversibly recycled to its pristine state by simply immersing it in a hydrochloric acid solution (1 M) for 30 min. These findings provide insights into fabricating various colorimetric sensors as non-imitable anticounterfeiting films with selective encryption/decryption for achieving forensic-level security.
To successfully develop a regioregular polymer, poly[4,8‐bis(5‐(2‐hexyldecyl)thiophen‐2‐yl)benzo[1,2‐ b :4,5‐ b ′]dithiophene][5,5′‐bis(7‐(4‐(2‐butyloctyl)thiophen‐2‐yl)‐6‐fluorobenzo[ c ][1,2,5]thiadiazol‐4‐yl)‐2,2′‐bithiophene] (PDBD‐FBT), a symmetric monomer synthesized in high yield by tin homo‐coupling reactions. PDBD‐FBT is suitable as a donor material in organic photovoltaics (OPVs) because it shows high crystallinity and strong face‐on packing properties. These properties were amplified by thermal annealing (TA). This causes a power conversion efficiency (PCE) enhancement in PDBD‐FBT‐based OPVs. Using PDBD‐FBT as a polymer donor and 2,2′‐((2 Z ,2′ Z )‐((12,13‐bis(2‐heptylundecyl)‐3,9‐diundecyl‐12,13‐dihydro‐[1,2,5]thiadiazolo[3,4‐ e ]thieno[2″,3″:4′,5′]thieno[2′,3′:4,5]pyrrolo[3,2‐ g ]thieno[2′,3′:4,5]thieno[3,2‐ b ]indole‐2,10‐diyl)bis(methanylylidene))bis(5,6‐difluoro‐3‐oxo‐2,3‐dihydro‐1 H ‐indene‐2,1‐diylidene))dimalononitrile (Y6‐HU) as an electron acceptor, a PCE of 7.91% was achieved without any additive and TA at optimized active layer film thickness of approximately 100 nm. After TA, a PCE of 12.53% was achieved with a 58% increase compared with the reference devices. Owing to the strong crystallinities, trap‐assisted recombination occurs by excessively formed grain boundaries; however, efficient exciton dissociation sufficiently covers these drawbacks. Even in the approximately 340 nm‐thick film condition, this tendency is more pronounced (73% PCE enhancement is observed from 6.17% to 10.69% of PCE in the without and with TA devices, respectively). Our study demonstrates that it is possible to manufacture thickness‐insensitive OPVs based on regioregular polymers with strong crystallinity and face‐on characteristics, thereby providing a solution to the thickness variation of large‐area organic solar cell modules.
In this work, a series of A-D-A'-D-A-type electron acceptors based on alkylated indacenodithiophene (C8IDT), dicyanated thiophene-flanked 2,1,3-benzothiadiazole (CNDTBT), and 2-(3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile (INCN) or 2-(5,6-difluoro-3-oxo-2,3-dihydro-1H-inden-1-ylidene) malononitrile (FINCN) are synthesized in order to investigate the effect of substituents on their photovoltaic properties. The corresponding CNDTBT-C8IDT-INCN and CNDTBT-C8IDT-FINCN acceptors vary in their optical, electrochemical, morphological, and charge transport properties. The fluorinated-INCN-based acceptor (CNDTBT-C8IDT-FINCN) exhibits lower energy levels, improved absorptivity, narrower π-π spacing, and prominent fibrillar structures when it is blended with poly[(2,6-(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)-benzo[1,2-b:4,5-b']dithiophene))-alt-5,5-(1',3'-di-2-thienyl-5',7'-bis(2-ethylhexyl)benzo [1',2'-c:4',5'-c']dithiophene-4,8-dione)] (PBDB-T). CNDTBT-C8IDT-FINCN exhibits a high power conversion efficiency (PCE) of 12.33% due to its high and well-balanced charge carrier mobility and distinct face-on orientation. Furthermore, large-area organic solar cells (OSCs) (active area: 55.45 cm2) with CNDTBT-C8IDT-FINCN exhibit a high PCE of 9.21%. This result demonstrates that CNDTBT-C8IDT-FINCN is a suitable and promising electron acceptor for large-area OSCs.
An acrylate monomer containing cyclotetrasiloxane (CTS) were designed and synthesized for anti-fouling coating applications. New acryl-based copolymers consisting of styrene and CTS, poly(styrene-co-CTS)s, were synthesized by changing molar ratios via free radical polymerization. The properties of poly(styrene-co-CTS)s were compared with those of poly(styrene) (PS) as a reference. The content of CTS in the copolymer increased its hydrophobicity also decreased whereas its surface decreased. Protein adsorption studies were conducted to evaluate their fouling-release properties.
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