Furan-containing conjugated polymers for organic solar cells

Development of organic semiconductors is one of the most intriguing and productive topics in material science and engineering. Many efforts have been made on the synthesis of aromatic building blocks such as benzene, thiophene and pyrrole due to the facile preparation accompanied by the intrinsic environmental stability and relatively efficient properties of the resulting polymers. In the past, furan has been less explored in this field because of its high oxidation potential. Recently, furan has attracted obsession due to its weaker aromaticity, the greater solubilities of furan-containing π-conjugated polymers relative to other benzenoid systems and the accessibility of furan-based starting materials from renewable resources. This review elaborates the advancements of organic photovoltaic polymers containing furan building blocks. The uniqueness and advantages of furan-containing building blocks in semiconducting materials are also discussed.     

Synthesis of the (X-DADAD)n-type conjugated polymers with 2,1,3-benzoxadiazole acceptor blocks and their application in organic solar cells

Two polymers with benzoxadiazole acceptor units were synthesized and investigated as electron donor materials in organic solar cells. Variation of the alkyl substituents was shown to significantly affect the optoelectronic properties of the polymers. In particular, the polymer HOMO energy level was lowered by 0.1 eV, while maintaining the same band gap, by replacement of the 2-ethylhexyl side-chains with the 2-hexyldecyl group. This modification also resulted in a higher open circuit voltage of the solar cells.     

Analysis of diverse direct arylation polymerization (DArP) conditions toward the efficient synthesis of polymers converging with stille polymers in organic solar cells

Despite the emergence of direct arylation polymerization (DArP) as an alternative method to traditional cross‐coupling routes like Stille polymerization, the exploration of DArP polymers in practical applications like polymer solar cells (PSCs) is limited. DArP polymers tend to have a reputation for being marginally inferior to Stille counterparts due to the increased presence of defects that result from unwanted side reactions in direct arylation, such as unselective C‐H bond activation and homocoupling. We report ten DArP protocols across the three major classes of DArP to generate poly[(2,5‐bis(2‐hexyldecyloxy)phenylene)‐alt‐(4,7‐di(thiophen‐2‐yl)benzo[c][1,2,5]thiadiazole)] (PPDTBT). Through evaluation of the method and resulting photophysical and electronic properties, we show not all DArP methods are suitable for generating device‐quality alternating copolymers. When DArP PPDTBT was synthesized in superheated THF with Cs₂CO₃, neodecanoic acid, and P(o‐anisyl)₃, it generated polymers of exceptional quality that performed comparably to Stille counterparts in both roll coated ITO‐free and spin‐coated ITO devices. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2907–2918     

Multifunctional triphenylamine polymers synthesized via direct (hetero) arylation polymerization

The design rules for creating multifunctional organic electronic materials are currently limited. By copolymerizing twisted triphenylamine (TPA) and electron rich dioxythiophene (XDOT) monomers via Direct (Hetero) Arylation Polymerization (DHAP), a set of polymers are obtained that perform as yellow to transmissive electrochromic (EC) films with up to 45% contrast, as well as in electroluminescent (EL) applications, achieving a luminance of ∼450 cd/m² in yellow‐green polymer light‐emitting diodes (PLEDs). In addition, polymerizing TPA with a donor‐acceptor‐donor monomer results in a low‐bandgap polymer that achieves power conversion efficiencies up to 2.5% when blended with PC₇₁BM in conventional organic photovoltaic (OPV) devices. Incorporation of TPA units into the polymer backbone largely breaks any aggregation and ordering in the solid‐state, leading to highly soluble materials that form smooth, reproducible thin films. The TPA unit also serves to break conjugation throughout the polymer backbone, providing precise control over optical and electronic properties through choice of comonomer. These results suggest that TPA copolymers can be useful for achieving multi‐functionality without sacrificing facile solution processability, making them promising candidates for multifunctional devices like dual EC/EL displays. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 147–153     

Diffusion of small molecules in glassy polymers

Small molecules in glassy polymers are considered to occupy sites with a distribution of free energies of dissolution. Then their diffusivity depends on concentration and temperature in the same way as it has been derived for hydrogen atoms in metallic glasses. For hydrogen it was shown that the tracer diffusion coefficient is proportional to the activity coefficient of the solute atoms. The latter can be evaluated from measured data of sorption of the small molecules in the polymer. Knowing this quantity, the thermodynamic factor can be calculated and the concentration dependence of the mutual diffusion coefficient is obtained in excellent agreement with published experimental results. New experimental results are presented for the diffusion coefficient of CO₂ in Kapton and four polycarbonates (BPA-PC, BPZ-PC, TMBPA-PC, and TMC-PC) in the low CO₂ pressure range of a few mbar up to 1 bar. The results are in agreement with the model developed for hydrogen. The reference diffusion coefficient, which is a fitting parameter of the model that is independent of the distribution of free energies is smallest for the polycarbonate BPZ-PC having a high γ-relaxation temperature. This correlation between the diffusion coefficient and the dynamics of the polymer can be found for other substituted polycarbonates as well. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 2397–2408, 1997     

Thienoisoindigo‐based small molecules and narrow bandgap polymers synthesized via C–H direct arylation coupling

Thienoisoindigo (TIIG) has emerged as an attractive building block for high‐performance organic optoelectronic devices. Here we report the first synthesis of a series of π‐conjugated TIIG‐based small molecules and alternating copolymers via direct C–H arylation, which enables the efficient synthesis without use of flammable and toxic orgametallic reagents in fewer steps compared Suzuki and Stille coupling. The direct arylation coupling between TIIG and two respective mono‐bromo aryl reactants clearly shows that the α‐H is more reactive than the β‐H in the thiophene unit of TIIG. The high regioselectivity of TIIG monomer warrants the successful synthesis of high‐quality alternating copolymers with minimal structural defects. PTIIG‐BT polymer synthesized via direct arylation polymerization (DAP) showed comparable molecular weight and hole mobility than the same polymer previously synthesized via Suzuki coupling. Moreover, the two new polymers (PTIIG‐TF and PTIIG‐2FBT) synthesized via DAP showed hole mobility up to 10^?3 cm² V^?1 s^?1 in FET devices fabricated and tested under ambient conditions. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2015–2031     

Preparation of semi‐alternating conjugated polymers using direct arylation polymerization (DArP) and improvement of photovoltaic device performance through structural variation

The results herein expand on optimized direct arylation polymerization (DArP) conditions for defect‐free poly[(2,5‐bis (2‐hexyldecyloxy)phenylene)‐alt‐(4,7‐di(thiophen‐2‐yl)benzo[c][1,2,5] thiadiazole)] (PPDTBT). Semi‐alternating and alternating donor–acceptor polymers containing alkoxy phenylene, dithienyl‐substituted thieno[3,4‐c]pyrrole‐4,6‐dione (DTTPD), and dithienyl‐substituted diketopyrrolopyrrole (DTDPP) were prepared via DArP, including a four‐component semi‐alternating copolymer PPDTDPPTPD. Variation of the alkoxy substituents on the phenylene donor including n‐hexyl, 2‐ethylhexyl, or 2‐hexyldecyl allowed for the tuning of thephysical and electronic properties. Molecular weights (M _n) ranged from 3.07 to 28.3 kDa for the PPDTTPD polymers and 2.63‐44.0 kDa for the PPDTDPP polymers, depending on the alkoxy substituents. Absorbance maxima and HOMO energies were varied from 550 to 602 nm and ?5.31 to ?5.69 eV for the PPDTTPD polymers and from 671 to 794 nm and ?5.41 to ?5.55 eV for the PPDTDPP polymers, respectively. Additive‐free, bulk heterojunction (BHJ) solar cells were fabricated, and the fill‐factors obtained (0.57–0.63) are some of the highest reported for polymers prepared using DArP. Higher molecular weight polymers for both PPDTTPD (28 kDa) and PPDTDPP (44 kDa) series performed poorly in solar cells. In contrast, the semi‐alternating polymers of lower M _n for the PPDTTPD (12.4 kDa) and PPDTDPP (9.05 kDa) series, incorporating both n‐hexyl and 2‐hexyldecyl alkoxy phenylene donors, provided power conversion efficiencies (PCE) of 3.26% and 3.49%, respectively. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 3370–3380     

水溶性共轭聚合物研究与应用进展

近年来,在水溶性共轭聚合物(CPs)方面的研究备受瞩目,由于它包含了聚合物共轭主链良好的光电性质的同时还兼具了良好的水溶性,因此在光电功能信息器件中有着特殊的应用,并显著地推动了包括生物传感、电致发光器件、太阳电池和场效应晶体管等有机光电子材料及其器件的发展.本文对近几年来水溶性CPs的合成及其应用进展做出简要的总结,...     

Diketopyrrolopyrrole‐based conjugated polymers and small molecules for organic ambipolar transistors and solar cells

The present highlight discusses major work in the synthesis of low bandgap diketopyrrolopyrrole ( DPP )‐based polymers with donor–acceptor–donor ( D–A–D ) approach and their application in organic electronics. It examines the past and recent significant advances which have led to development of low bandgap DPP ‐based materials with phenyl and thiophene as donors. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4241–4260     

Effective design of A-D-A small molecules for high performance organic solar cells via F atom substitution and thiophene bridge

Three novel small molecules with acceptor-donor-acceptor (A-D-A) configuration, SBDT1, SBDT2 and SBDT3, where 4,8-bis(octyloxy)benzo[1,2-b:4,5-b′]dithiophene (BDT) as the electron-donating core connecting to thiophene-substituted benzothiadiazole (BT) as electron-withdrawing are reported. The effects of fluorine atoms on the photophysical properties by introducing different fluorine atoms into the benzothiadiazole unit were investigated. These SBDTs exhibit good thermal stability, excellent panchromatic absorption in solution and film. SBDT2 and SBDT3 with fluorine-substituted BT possess a relatively deeper the highest occupied molecular orbital (HOMO). These A-D-A type molecules were treated as donor and PC₇₁BM as acceptor in bulk heterojunction (BHJ) small-molecule organic solar cells (SMOSCs). Among them, device based on SBDT2 gave the best device performance with a PCE of 5.06% with J_sc of 10.56 mA/cm², V_oc of 0.85 V, fill factor (FF) of 56.4%. These studies indicate that proper incorporation of fluorine atoms is an effective way to increase the efficiency of organic solar cells.     

Synthesis of conjugated polymers possessing diketopyrrolopyrrole units bearing phenyl,pyridyl, and thiazolyl groups by direct arylation polycondensation: Effects of aromatic groups in DPP on physical properties

Conjugated polymers containing phenyl‐, pyridyl‐, and thiazolyl‐flanked diketopyrrolopyrrole (DPP) were synthesized by direct arylation polycondensation of 3,4‐ethylenedioxythiophene derivatives and dibrominated DPP‐based monomers, in order to probe the effects of the aromatic groups in the DPP units on the absorption property, energy level, and crystallinity. A polymer possessing thiazolyl‐flanked DPP units was found to display long‐wavelength absorption properties and higher crystallinity than the polymers bearing phenyl‐ and pyridyl‐flanked DPP units. These features of the thiazolyl‐based polymer were afforded by its coplanar structure of the main chain. The synthesized polymers showed semiconducting properties in organic field effect transistors and organic photovoltaics. Direct arylation polycondensation is an efficient synthetic method that affords a series of DPP‐based polymers in a simple fashion and, thus, helping in a comprehensive understanding on the relationship between the aromatic groups in DPP units and their physical properties. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2337–2345     

Effective design of A-D-A small molecules for high performance organic solar cells via F atom substitution and thiophene bridge

Novel A-D-A-type small molecule donors employ thiophene bridge and F-substitution to improve the power conversion efficiency in organic solar cell.     

Recent developments of di-amide/imide-containing small molecular non-fullerene acceptors for organic solar cells

Non-fullerene organic solar cells have received increasing attentions in these years, and great progresses have been made since 2013. Among them, aromatic di-amide/imide-containing frameworks have shown promising applications. The outstanding properties of them are highly associated with their unique electronic and structural features, such as strong electron-withdrawing nature, broad absorption in UV-visible region, tunable HOMO/LUMO energy levels, easy modifications, and excellent chemical, thermal and photochemical stabilities. In this review, we give an overview of recent developments of aromatic diamide/imide-containing small molecules used as electron acceptors for organic solar cells.     

A resonance light scattering ratiometry applied for binding study of organic small molecules with biopolymer

Resonance light scattering (RLS) technique is a creative application of light scattering signals detected by using a common spectrofluorometer, but it has drawbacks such as the fluctuation of signals caused by poorly quantified or variable factors. Herein we develop a RLS ratiometry to overcome the drawbacks of the technique and apply to measure the binding nature of organic small molecules (OSM) with biopolymer using the binding of cation porphyrins with heparin (HP) as an example. In near neutral solution, cationic porphyrins meso-tetrakis [(trimethylammoniumyl) phenyl] porphyrin (TAPP) and meso-tetra (4-methylpyridy) porphyrin (TMPyP-4) interact with heparin, resulting in hypochromatic effect, and enhanced RLS signals. Linear relationship could be established between the ratio of enhanced RLS signals at two wavelengths, where the maximum and minimum are available in the ratio curve of UV-vis spectrum of porphyrin to that of heparin-porphyrin complex, and the logarithm of heparin concentration, and thus a wide dynamic range detection method of biopolymers could be developed. In comparison with RLS method, this RLS ratiometric one is less affected by environmental conditions such as pH, ionic strength. The mechanism of these interactions was investigated based on the charge density distribution of the two porphyrin molecules and it could be concluded that the enhanced RLS intensity is proportionally promoted by the charge capacity of components in the complex. Additionally, the binding number and binding constant were measured scientifically by Scatchard plot.     

Synthesis of ultraviolet curable encapsulating adhesives and their package applications for organic optoelectronic devices

With conventional heating process, ultraviolet (UV) illumination, and microwave irradiation, we have successfully synthesized UV curable encapsulating adhesives with excellent gas barrier capabilities, good adhesive strength, moderate hardness, and high refractive indices. The experimental results manifest that the physical properties of lab-made encapsulating adhesives are highly dependent on their chemical structures and synthetic procedure. We also discover that the encapsulating adhesive prepared by microwave irradiation (i.e. encapsulating adhesive VI-MW) exhibits better adhesive strength and higher gas resistance than those prepared by conventional heating process and UV illumination. Furthermore, encapsulating adhesive VI-MW has also been applied for the package of organic light emitting diodes (OLEDs), flexible OLEDs, and organic solar cells. With encapsulating adhesive VI-MW, the entry of oxygen and moisture in the air into these organic optoelectronic devices has been blocked, therefore enhancing the lifetimes.     

Computational prediction of the properties of bis(ethynylthienyl)dialcoxynaphthalene-based conjugated polymers for organic solar cell applications

A series of homo- ( P0 ) and copolymers ( P1-P5 ) based on the electron-donor building-block 2,2′-(2,3-bis(2-ethylhexyloxy)naphthalene-1,4-diyl)bis(ethyne-2,1-diyl)dithiophene (1,4-NET) including ethynyl linkers aiming to promote coplanarity were designed, and their properties predicted using theoretical methodologies to evaluate their potential in organic solar cell applications. The geometries, FMO levels, energy bandgaps, and absorption spectra of trimer models were determined using time-dependent density functional theory, while their photovoltaic and charge-transport properties were estimated by the Scharber's model and semiclassical Marcus theory, respectively. Compared to high-performance conjugated polymers (CPs), such as PTB7-Th or PM6, and similar systems based on the 1D-BDT unit, the HOMO and LUMO levels of P0-P5 tend to be higher. In addition, the new CPs have complementary absorptions with narrow-bandgap acceptors, such as ITIC and Y6, and adequate matches between their HOMO and LUMO levels. Although the simulated photovoltaic and charge-transport properties could be overestimated, the best candidate to be synthesized and tested in organic solar cells is P5 due to its suitable and well-balanced properties, demonstrating the positive effect of incorporating ethynyl bridges to improve the optoelectronic properties of CPs.     

Optimization of direct arylation polymerization (DArP) through the identification and control of defects in polymer structure

As a newly emerged protocol for the synthesis of conjugated polymers, direct arylation polymerization (DArP) is an environmentally friendly and cost-effective alternative to traditional methods of polymerization. DArP efficiently yields conjugated polymers with high yield and high molecular weight. However, DArP is also known to produce defects in polymer chemical structure. Together with molecular weight and polydispersity, these defects are considered to be important parameters of polymer structure and they have a strong impact on optical, electronic and thermal properties of conjugated polymers. The four major classes of conjugated polymer defects inherent for DArP have been identified: homocoupling regiodefects, branching defects, end group defects, and residual metal defects. To have a precise control over the polymer properties, it is important to understand what causes the defects to form during the polymerization process and be able to control their content. Here within the scope of current literature, we discuss in detail the definition and origin of all these defects, their influence on polymer properties and effective means to control the defects through fine tuning of the DArP reaction parameters. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 135–147     

Optimization of direct arylation polymerization conditions for the synthesis of poly(3‐hexylthiophene)

Direct arylation polymerization (DArP) is an emerging alternative to Stille and Suzuki polymerizations. This method is attractive as it allows preparation of high‐molecular‐weight conjugated polymers in good yield without the need to metallate monomers. Despite this promise, for poly(3‐hexylthiophene) (P3HT) and related polymers that have β‐protons on the thiophene ring, DArP is known to produce β‐defects, which make the polymer properties different from polymers produced by traditional methods. Here, we demonstrate that DArP conditions based on simple, inexpensive, and bench‐stable reagents can be tuned to limit the amount of defects and produce P3HT with properties remarkably similar to Stille P3HT. Specifically, lowering the reaction temperature, lowering the amount of catalyst, and using a bulkier carboxylate ligand is critical. Optimized conditions include reacting 2‐bromo‐3‐hexylthiophene with 0.25 mol % of Pd(OAc)₂, 1.5 equivalents of K₂CO₃, and 0.3 equivalents of neodecanoic acid in N,N‐dimethylacetamide at 70 °C and give DArP P3HT with ～60% yield, regioregularity of 93.5%, molecular weight of 20 kDa, polydispersity of 2.8, and melting point of 217 °C, providing a very close match to Stille P3HT, which is obtained with 70–80% yield, 91–94% regioregularity, molecular weight of 15–25 kDa, polydispersity of 2.5–2.8, and melting point of 214–221 °C. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2660–2668