Three novel dithieno[3,2‐b:2′,3′‐d]thiophene‐based low‐bandgap polymers are synthesized by a Suzuki–Miyaura coupling reaction or by direct arylation polycondensation. The polymers present a high molecular weight (26–32 kDa) and narrow polydiversity (1.3–1.7). With a highest occupied molecular orbital (HOMO) energy level around ?5.20 eV, these polymers exhibit a narrow bandgap of 1.75–1.87 eV. All the polymers display strong absorption in the range of 350–700 nm. Bulk‐heterojunction (BHJ) solar cells are further fabricated by blending the as‐prepared polymer with (6,6)‐phenyl‐C61‐butyric acid methyl ester (PC61BM) at different weight ratios. The best devices contribute a power conversion efficiency (PCE) of 0.73% under AM 1.5 (100 mW cm?2).
A semicrystalline low‐bandgap polymer (PDTPBT) based on alternating dithienopyrrole and benzothiadiazole moieties as a pair of the indene‐C60 bisadduct (ICBA) for polymeric solar cells is reported. The lowest unoccupied molecular orbital (LUMO) level of PDTPBT is measured to be ?3.47 eV, ensuring sufficient energy offset for photoinduced charge transfer to ICBA. Photovoltaic cells are fabricated with ICBA and [6,6]‐phenyl‐C71‐butyric acid methyl ester (PC71BM) as an acceptor. By replacing PC71BM with ICBA, the open‐circuit voltage is increased by 0.23 V and the resulting power conversion efficiency is improved from 1.17% to 1.71%. To optimize the ICBA‐based devices, crystalline low‐bandgap structures should be designed carefully as a pair of ICBA by considering the energy‐level offset for charge separation and crystalline interchain ordering, for minimizing the intercalated ICBAs inside the polymer domain.
In order to regulate the electronic ability of benzo[1,2‐b:4,5‐b′]dithiophene (BDT), the new electron‐donating unit (BDTOT) is designed and synthesized which consists of a BDT backbone with conjugated 2‐(2‐ethylhexyl)‐3,4‐dimethoxythiophene side chains. By alternating copolymerization of BDTOT with electron‐accepting units of fluorinated benzothiadiazole (FBT), benzothiadiazole (BT), and pyrrolo[3,4‐c]pyrrole‐1,4‐dione (DPP), three donor–acceptor (D‐A) copolymers (PBDTOT‐FBT, PBDTOT‐BT, and PBDTOT‐DPP) have been developed for PSC applications. The impact of dimethoxythiophene substituent and the electron‐accepting strength of the acceptor units on the absorption, HOMO/LUMO energy levels, and photovoltaic properties of the resultant polymers is investigated in detail. PBDTOT‐BT and PBDTOT‐DPP exhibit relatively narrower bandgaps and PBDTOT‐FBT possesses a down‐shifted HOMO energy level as compared to their corresponding analogs without methoxy groups onto the conjugated thiophene side chains. The screening of the different blend ratio, the processing additive, and polar solvent post‐treatment is conducted to optimize the polymer solar cell (PSC) devices. PSCs with PBDTOT‐FBT as donor deliver a power conversion efficiency (PCE) of 2.55%. By treatment of the active layer with methanol to tailor the morphology, the solar cell based on PBDTOT‐FBT exhibits the remarkably improved PCE of 4.84% with a Voc of 0.92 V, a Jsc of 8.71 mA cm?2, and an FF of 60.3%.
Stille coupling polymerization is used to synthesize a new donor–acceptor (D–A) conjugated random copolymer (PBDT‐DFB‐DPP) that comprises an electron‐rich benzodithiophene (BDT) unit in conjugation with electron‐deficient 2,5‐difluorobenzene (DFB) and diketopyrrolopyrrole (DPP) moieties, which have complementary light‐absorption behavior. The thermal, photophysical, and electrochemical properties of the polymer are investigated using thermogravimetric analysis, UV–vis absorption spectroscopy, and cyclic voltammetry. The random copolymer exhibits both broad light absorption and a low‐lying highest occupied molecular orbital (HOMO) level, which contribute to enhancement of the short‐circuit current density (Jsc) and open‐circuit voltage (Voc). A bulk‐heterojunction polymer solar cell fabricated from PBDT‐DFB‐DPP and PC60BM exhibits a promising power conversion efficiency (PCE) of 2.50%.
Novel biaxially extended octithiophene (8T)‐based conjugated polymers are successfully synthesized using Stille coupling reactions of the branched octithiophene moiety with selenophene (P8TSe), thiophene (P8TT), and thieno[3,2‐b]thiophene (P8TTT). The 8T moiety can significantly lower the highest occupied molecular orbital (HOMO) level and leads to an enhanced open‐circuit voltage because of the branched conformation. The power conversion efficiencies (PCE) of the polymer/[6,6]‐phenyl‐C71‐butyric acid methyl ester PC71BM photovoltaic cells are in the range of 1.28–2.30%. In particular, the P8TTT‐based device processed from an o‐dichlorobenzene/1,8‐diiodoctane mixed solvent shows the best PCE among the studied polymers (2.81%), demonstrating that 8T‐based polymers with a low HOMO level can emerge as promising candidates for organic device applications.
Three medium‐bandgap polymers based on a 4,5‐ethylene‐2,7‐dithienyl carbazole as the electron‐donating unit and different 5,6‐dialkoxy‐2,1,3‐benzothiadiazoles as the electron‐accepting units, are synthesized as polymer donors for photovoltaic applications. The three copolymers possess highest occupied molecular oribital (HOMO) levels around ?5.47 eV and medium bandgaps of about 1.94 eV. The solar cells with polymer:[6,6]‐phenyl C71‐butyric acid methyl ester (PC71BM) = 1:4 as the active layer, show an especially high open‐circuit voltage (Voc) of 0.95 V and attain good power conversion efficiency up to 5.91%. The hole mobilities of the active layer films, measured by space‐charge‐limited current (SCLC), are up to 3.5 × 10?4 cm2 V?1 s?1. Given the favorable medium bandgaps, low‐lying HOMO levels, and good hole mobilities, these copolymers are promising candidates for the construction of a highly efficient front cell to harvest the shorter wavelength band of the solar radiation in a tandem solar cell with high Voc.
A new D–A copolymer ( PBDT‐DTQx) based on the 2,3‐di(5‐hexylthiophen‐2‐yl)quinoxaline acceptor unit and a bithienyl‐substituted benzodithiophene (BDT) donor unit is designed and synthesized for application as the donor material in polymer solar cells (PSCs). The polymer film shows a broad absorption band covering the wavelength range from 300 to 720 nm and a low highest occupied molecular orbital (HOMO) energy level at ?5.35 eV. A device based on PBDT‐DTQx :PC70BM ([6,6]‐phenyl‐C71‐butyric acid methyl ester) (1:2.5, w/w) with chloronaphthalene as a solvent additive displays a power conversion efficiency (PCE) of 3.15%. With methanol treatment, the PCE of the PSCs is further improved to 3.90% with a significant increase of the short‐circuit current density, Jsc, from 10.10 mA cm?2 for the device without the methanol treatment to 11.71 mA cm?2 for the device with the methanol treatment.
To study the influence of the spacer between the donor (D) and acceptor (A) units in a side chain on the photophysical and photovoltaic performance, a novel side‐chain D–A conjugated copolymer of PDPAT‐BDT‐BT is made, which contains binary donor units of N,N‐diphenylthiophen‐2‐amine (DPAT) and benzo[1,2‐b:4,5‐b′]dithiophene (BDT) in the main chain and an appending benzothiadiazole (BT) acceptor unit in the side chain. Compared with its counterpart of PDPAT‐BDT‐BT, which has an additional phenyl spacer between the DPAT and BT units, this PDPAT‐BDT‐BT exhibits a smaller optical bandgap, a broader absorption range, and a lower highest occupied molecular orbital (HOMO) energy level (?5.42 eV), as well as improved photovoltaic properties in bulk heterojunction polymer solar cells containing [6,6]‐phenyl‐C71‐butyric acid methyl ester as an electron acceptor. A maximum power conversion efficiency of 3.27% with an open circuit voltage of 0.87 V and a fill factor of 49.8% are obtained in the cells. This work indicates that the photophysical and photovoltaic performance of the side‐chain D–A polymers in polymer solar cells can be significantly improved by shortening the phenyl spacer between the D and A units.
Unsaturated polyesters are synthesized via ring‐opening copolymerization of α‐methylene‐δ‐valerolactone and δ‐valerolactone. These polyesters 4a–c are mixed with ethyl methacrylate (EMA), 2‐hydroxyethyl methacrylate (HEMA), and α‐methylene‐δ‐valerolactone (α‐MVL), respectively. Then, crosslinking is carried out by free radical polymerization initiated by an azo‐initiator. A second glass transition is found with incorporation of HEMA and α‐MVL. These findings indicate the formation of phase‐separated polyester blocks crosslinked with the poly(meth)‐acrylic‐segments, respectively poly(α‐methylene‐δ‐valerolactone) segments.
N‐vinylcaprolactam (NVCL) is modified via alkylation at the α‐position. The α‐substituents are ethyl (3‐ethyl‐1‐vinylcaprolactam), dodecyl (3‐dodecyl‐1‐vinylcaprolactam), octadecyl (3‐octadecyl‐1‐vinylcaprolactam), 1‐propanol (3‐(3‐hydroxy‐propyl)‐1‐vinylcaprolactam), and PEG3 bromide (3‐PEG3‐bromide‐1‐vinylcaprolactam). These monomers are homo‐ and copolymerized with N‐(4‐methylphenyl)maleimide by the free radical mechanism. The structures of the obtained polymers are characterized by means of 1H NMR and IR spectroscopy, gel permeation chromatography (GPC), and by use of differential scanning calorimetry (DSC) (Tg).
In this paper, a series of polysiloxanes, presenting different contents of densely simple and well‐defined short‐branched chains (G1–G5), are prepared by hydrosilylation of α,ω‐(dimethylvinylsiloxy)‐poly(dimethyl‐methylvinyl)siloxanes (P1–P5) with 1,1,1,3,5,5,5‐heptamethyltrisiloxane (MDHM) and characterized by 1H and 29Si nuclear magnetic resonance, Fourier transform‐infrared spectroscopy, Abbe refractometry, gel permeation chromatography, and differential scanning calorimetry. The rheological behaviors of the G1–G5 products are investigated to study the influences of the short‐branched chains. The rheological parameters including non‐Newtonian index (n ) and the flow activation energy (ΔEη) are obtained and discussed. It is observed that the G1–G5 polymers belonged to pseudoplastic fluids and the ΔEη values of the G1–G5 products are significantly influenced by the short‐chain branching degree of the polymers.
Two electron‐deficient tetracyclic monomers, 6,9‐dibromo‐7,8‐bis(octyloxy)‐11H‐indeno[2,1‐b] quinoxalin‐11‐one ( M1 ) and 1,3‐bis(5′‐bromo‐4′‐hexylthiophen‐2‐yl)‐9H‐indeno[1,2‐b]thieno[3,4‐e]pyrazin‐9‐one ( M2 ), are synthesized through condensation of ninhydrin with aromatic diamines in good yields. Copolymerization of M1 with thiophene (Th) and dithieno[3,2‐b:2′,3′‐d]silole (DTS), and M2 with DTS affords three new D–A conjugated copolymers, P1 – P3, respectively . The optical, electrochemical, and photovoltaic properties of P1–P3 are investigated. P3 exhibits a broad absorption (300–1100 nm) and a low bandgap of 1.24 eV. Solar cells based on P3 /[6,6]‐phenyl C71 butyric acid methyl ester (PC71BM) blends afford a power conversion efficiency of 1.93% and a very broad spectral response (300–1020 nm).
The homo‐ and copolymerizations of 1,3‐butadiene and isoprene are examined by using neodymium isopropoxide [Nd(Oi‐Pr)3] as a catalyst, in combination with a methylaluminoxane (MAO) cocatalyst. In the homopolymerization of 1,3‐butadiene, the binary Nd(Oi‐Pr)3/MAO catalyst works quite effectively, to afford polymers with high molecular weight ( ≈ 105 g mol‐1), narrow molecular‐weight distribution (MWD) (/ = 1.4–1.6), and cis‐1,4‐rich structure (87–96%). Ternary catalysts that further contain chlorine sources enhance both catalytic activity and cis‐1,4 selectivity. In the copolymerization of 1,3‐butadiene and isoprene, the copolymers feature high , unimodal gel‐permeation chromatography (GPC) profiles, and narrow MWD. Most importantly, the ternary Nd(Oi‐Pr)3/MAO/t‐BuCl catalyst affords a copolymer with high cis‐1,4 content in both monomer units (>95%).
Randomly methylated β‐cyclodextrin (me‐β‐CD) is used to include the hydrophobic monomer N‐(4‐methylphenyl)maleimide (MPM) ( 1 ) yielding the corresponding water‐soluble host‐guest structure 1a . Free‐radical copolymerization of 1a with N‐vinylpyrrolidone (NVP) ( 2 ) is performed and the reactivity ratios r1 and r2 are determined: 0.24 ± 0.03 (r2) and 1.10 ± 0.05 (r1a). This indicates a preferred incorporation of complexed maleimide into the copolymer chain. In contrast to that, the copolymerization of the uncomplexed monomers 1 and 2 is carried out using organic solvent (DMF/H2O) showing reactivity ratios corresponding to nearly alternating copolymerization (r2 = 0.09 ± 0.02; r1 = 0.34 ± 0.03).
In the current investigation, nanocomposites containing a β‐nucleated poly(propylene‐co‐ethylene) (PPR) matrix filled with untreated (SiO2) and methacrylate‐modified silica nanoparticles (SiO2‐MAA) are prepared. Transmission electron microscopy (TEM) reveals the improvement in the quality of dispersion due to the surface modification of the nanoparticles. Also, from differential scanning calorimetry (DSC) and X‐ray diffraction (XRD), it is found that the β‐nucleating agent and silica nanoparticles work synergistically in order to increase the relative β‐content in the nanocomposite samples. The thermal stability of each samples is evaluated by means of thermogravimetric analysis (TGA) and the enhancement of the thermal stability of the nanocomposites is attributed to the nanoconfinement of the macromolecular chains caused by the presence of the fillers.
A kind of γ‐(cyclodextrin) (γ‐CD)‐based polyrotaxane (PR) is synthesized via an aqueous click reaction between propargylamine‐substituted β‐CD and polypseudorotaxanes (PPRs) self‐assembled from azido‐endcapped PNIPAAm‐b‐Pluronic F68‐b‐PNIPAAm with a varying amount of γ‐CD. The evolution of the self assembly, dependent on the preparation process, is observable by X‐ray diffraction (XRD) and DSC analyses. The γ‐CD is able to be included and preferably entrapped on the PNIPAAm blocks, showing a unique loose‐fit aggregate structure after the click reaction. Most γ‐CDs gradually slip over to the middle PPG block of Pluronic F68, giving rise to a characteristic channel‐type crystal structure in the dialysis process. In addition, the lower critical solution temperature (LCST) is sharply enhanced due to the coverage of the remaining γ‐CDs hindering the thermally responsive aggregation of the PNIPAAm blocks.
A novel polymer semiconductor based on squaric acid is successfully prepared through polycondensation reaction. Physicochemical properties of polysquaraine are explored by Fourier transform infrared (FT‐IR) and ultraviolet‐visible (UV‐vis) absorption spectroscopy, thermogravimetric/modulated temperature differential scanning calorimetry (TGA/MTDSC) analyses, and cyclic voltammetry (CV). Next, the charge carrier properties are investigated through the fabrication and characterization of field‐effect transistors (FETs) using solution‐processed polymeric films. It is found that the polysquaraine is FET active and exhibits decent p‐type mobilities (up to 5 × 10−4 cm2 V−1 s−1), which illustrates the promising properties of this semiconductor in optoelectronics. Notably, there is no precedent for the use of squaraine‐based polymers in field‐effect transistors. Bulk heterojunction solar cells (BHJ‐OSCs) are finally prepared from the blends of polysquaraine with the fullerene derivative [6,6]‐phenyl‐C71‐butyric acid methyl ester (PC71BM). Power conversion efficiencies up to 0.86% are achieved for nonoptimized system under simulated air mass 1.5 (AM1.5) conditions.
A diamine monomer with trifluoromethyl groups, 3,3′‐bis(trifluoromethyl)‐4,4′‐diamino‐1,1′‐biphenyl, is synthesized from 5‐bromo‐2‐nitrobenzotrifluoride with two steps. The model reaction with monofunctional benzoyl chloride at room temperature gives the model compound with a quantitative yield. The results of the model reaction indicate that the amine groups have sufficient reactivity in spite of the presence of electron‐withdrawing and bulky trifluoromethyl group at the ortho position. The monomer is polymerized with terephthaloyl chloride and isophthaloyl chloride in N,N‐dimethylacetamide (DMAc) or DMAc containing LiCl using pyridine as an acid acceptor at room temperature. All synthesized polymers are somewhat crystalline and colorless. While the meta‐linked polyamide ( PA2 ) shows excellent solubility in polar aprotic solvents, the para‐linked one ( PA1 ) is dissolved in polar aprotic solvents containing LiCl and concentrated H2SO4. They show good thermal and thermooxidative stability as well as high melting temperatures.
Molecular‐recognition‐responsive characteristics of a novel poly(N‐isopropylacrylamide‐co‐benzo‐12‐crown‐4‐acrylamide) (PNB12C4) hydrogel have been investigated. In the prepared PNB12C4 hydrogel, benzo‐12‐crown‐4 (B12C4) groups act as guest molecules and γ‐cyclodextrin (γ‐CD)‐receptors, and poly(N‐isopropylacrylamide) (PNIPAM) networks act as phase‐transition actuators. The formation of stable γ‐CD/B12C4 complexes enhances the hydrophilicity of the PNB12C4 hydrogel networks, and induces positive shift of the volume phase transition temperature (VPTT) of PNB12C4 hydrogel. Moreover, the PNB12C4 hydrogel also shows thermoresponsive adsorption property selectively towards γ‐CD. The γ‐CD‐recognition sensitivity of PNB12C4 hydrogel can be dramatically improved by increasing γ‐CD concentration in solution or B12C4 content in PNB12C4 copolymer networks. The results in this study provide valuable information for developing crown ether‐based smart materials in various applications.
Here, the synthesis, characterization, and photovoltaic properties of four new donor–acceptor copolymers are reported. These copolymers are based on 4,4‐difluoro‐cyclopenta[2,1‐b:3,4‐b′] dithiophene as an acceptor unit and various donor moieties: 4,4‐dialkyl derivatives of 4H‐cyclopenta[2,1‐b:3,4‐b′]dithiophene and its silicon analog, dithieno[3,2‐b:2′,3′‐d]‐silol. These copolymers have an almost identical bandgap of 1.7 eV and have a HOMO energy level that varies from ?5.34 to ?5.73 eV. DSC and X‐ray diffraction (XRD) investigations reveal that linear octyl substituents promote the formation of ordered layered structures, while branched 2‐ethylhexyl substituents lead to amorphous materials. Polymer solar cells based on these copolymers as donor and PC61BM as acceptor components yield a power conversion efficiency of 2.4%.
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