Fluorene‐based alternating polymers containing electron‐withdrawing bithiazole units: Preparation and device applications

We report here the synthesis via Suzuki polymerization of two novel alternating polymers containing 9,9‐dioctylfluorene and electron‐withdrawing 4,4′‐dihexyl‐2,2′‐bithiazole moieties, poly[(4,4′‐dihexyl‐2,2′‐bithiazole‐5,5′‐diyl)‐alt‐(9,9‐dioctylfluorene‐2,7‐diyl)] (PHBTzF) and poly[(5,5′‐bis(2″‐thienyl)‐4,4′‐dihexyl‐2,2′‐bithiazole‐5″,5″‐diyl)‐alt‐(9,9‐dioctylfluorene‐2,7‐diyl)] (PTHBTzTF), and their application to electronic devices. The ultraviolet–visible absorption maxima of films of PHBTzF and PTHBTzTF were 413 and 471 nm, respectively, and the photoluminescence maxima were 513 and 590 nm, respectively. Cyclic voltammetry experiment showed an improvement in the n‐doping stability of the polymers and a reduction of their lowest unoccupied molecular orbital energy levels as a result of bithiazole in the polymers' main chain. The highest occupied molecular orbital energy levels of the polymers were ?5.85 eV for PHBTzF and ?5.53 eV for PTHBTzTF. Conventional polymeric light‐emitting‐diode devices were fabricated in the ITO/PEDOT:PSS/polymer/Ca/Al configuration [where ITO is indium tin oxide and PEDOT:PSS is poly(3,4‐ethylenedioxythiophene) doped with poly(styrenesulfonic acid)] with the two polymers as emitting layers. The PHBTzF device exhibited a maximum luminance of 210 cd/m² and a turn‐on voltage of 9.4 V, whereas the PTHBTzTF device exhibited a maximum luminance of 1840 cd/m² and a turn‐on voltage of 5.4 V. In addition, a preliminary organic solar‐cell device with the ITO/PEDOT:PSS/(PTHBTzTF + C₆₀)/Ca/Al configuration (where C₆₀ is fullerene) was also fabricated. Under 100 mW/cm² of air mass 1.5 white‐light illumination, the device produced an open‐circuit voltage of 0.76 V and a short‐circuit current of 1.70 mA/cm². The fill factor of the device was 0.40, and the power conversion efficiency was 0.52%. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1845–1857, 2005     

New copolymers with thieno[3,2‐b]thiophene or dithieno[3,2‐b:2′,3′‐d]thiophene units possessing electron‐withdrawing 4‐cyanophenyl groups: Synthesis and photophysical,electrochemical, and electroluminescent properties

New monomers containing 4‐cyanophenyl (–PhCN) groups attached to a thieno[3,2‐b]thiophene (TT) or dithieno[3,2‐b:2′,3′‐d]thiophene (DTT) structure were synthesized and characterized as 4‐(2,5‐dibromothieno[3,2‐b]thiophen‐3‐yl)benzonitrile (Br–TT–PhCN) or 4,4′‐(2,6‐dibromodithieno[3,2‐b:2′,3′‐d]thiophene‐3,5‐diyl)dibenzonitrile (Br–DTT–PhCN). The Suzuki coupling of 9,9‐dioctylfluorene‐2,7‐diboronic acid bis(1,3‐propanediol)ester and the Br–TT–PhCN or Br–DTT–PhCN monomer was utilized for the syntheses of novel copolymers poly{9,9‐dioctylfluorene‐2,7‐diyl‐alt‐3‐(4′‐cyanophenyl)thieno[3,2‐b]thiophene‐2,5‐diyl} (PFTT–PhCN) and poly{9,9‐dioctylfluorene‐2,7‐diyl‐alt‐3,5‐bis(4′‐cyanophenyl)dithieno[3,2‐b:2′,3′‐d]thiophene‐2,6‐diyl} (PFDTT–PhCN), respectively. The photophysical, electrochemical, and electroluminescent (EL) properties of these novel copolymers were studied. Their photoluminescence (PL) exhibited the same emission maximum for both copolymers in solution. Red‐shifted PL emissions were observed in the thin films. The PL emission maximum of PFTT–PhCN was more significantly redshifted than that of PFDTT–PhCN, indicating more pronounced excimer or aggregate formation in PFTT–PhCN. The ionization potential (HOMO level) and electron affinity (LUMO level) values were 5.54 and 2.81 eV, respectively, for PFTT–PhCN and were 5.57 and 2.92 eV, respectively, for PFDTT–PhCN. Polymer light‐emitting diodes (LEDs) with copolymer active layers were fabricated and studied. Anomalous behavior and memory effects were observed from the current–voltage characteristics of the LEDs for both copolymers. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2629–2638     

Relationship between the liquid crystallinity and field‐effect‐transistor behavior of fluorene–thiophene‐based conjugated copolymers

A series of fluorene–thiophene‐based semiconducting materials, poly(9,9′‐dioctylfluorene‐alt‐α,α′‐bisthieno[3,2‐b]thiophene) (F8TT2), poly(9,9′‐di(3,6‐dioxaheptyl)fluorene‐alt‐thieno[3,2‐b]thiophene) (BDOHF8TT), poly(9,9′‐di(3,6‐dioxaheptyl)fluorene‐alt‐bithiophene) (BDOHF8T2), and poly(9,9′‐dioctylfluorene‐co‐bithiophene‐co‐[4‐(2‐ethylhexyloxyl)phenyl]diphenylamine) (F8T2TPA), was synthesized through a palladium‐catalyzed Suzuki coupling reaction. F8TT2, BDOHF8TT, BDOHF8T2, and F8T2TPA films exhibited photoluminescence maxima at 523, 550, 522, and 559 nm, respectively. Solution‐processed field‐effect transistors (FETs) fabricated with all the copolymers except F8T2TPA showed p‐type organic FET characteristics. Studies of the differential scanning calorimetry scans and FETs of the polymers revealed that more crystalline polymers gave better FET device performance. The greater planarity and rigidity of thieno[3,2‐b]thiophene in comparison with bithiophene resulted in higher crystallinity of the polymer backbone, which led to improved FET performance. On the other hand, the random incorporation of the triphenylamine moiety into F8T2TPA caused the polymer chains to lose crystallinity, resulting in an absence of FET characteristics. With this study, we could assess the liquid‐crystallinity dependence of the field‐effect carrier mobility on organic FETs based on liquid‐crystalline copolymers. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4709–4721, 2006     

Synthesis and characterization of fluorene‐based low‐band gap copolymers containing propylenedioxythiophene and benzothiadiazole derivatives for bulk heterojunction photovoltaic cell applications

The following noble series of soluble π‐conjugated statistical copolymers was synthesized by palladium catalyzed Suzuki polymerization: poly[(9,9‐dioctylfluorene)‐alt‐(4,7‐bis(3′,3′‐dihepyl‐3,4‐propylenedioxythienyl)‐2,1,3‐benzothiadiazole)] (PFO‐PTBT) derived from poly(9,9‐dioctylfluorene) (PFO) and poly[(4,7‐bis(3′,3′‐dihepyl‐3,4‐propylenedioxythienyl)‐2,1,3‐benzothiadiazole)] poly(heptyl₄‐PTBT). The structure and properties of these polymers were characterized using ¹H‐, ¹³C‐NMR, UV–visible spectroscopy, elemental analysis, GPC, DSC, TGA, photoluminescence (PL), and cyclic voltammetry (CV). The statistical copolymers, PFO‐PTBT (9:1, 8.4:1.6, 6.5:3.5), were soluble in common organic solvents and easily spin coated onto indium‐tin oxide (ITO) coated glass substrates. The weight‐average molecular weight (M_w) and polydispersity of the PFO‐PTBT ranged from (1.0–4.2) × 10⁴ and 1.5–2.3, respectively. Bulk heterojunction photovoltaic cells with an ITO/PEDOT/PFO‐PTBT:PCBM/LiF/Al configuration were fabricated, and the devices using PFOPTBT (6.5:3.5) showed the best performance compared with those using PFO‐PTBT (9:1, 8.4:1.6). A maximum power conversion efficiency (PCE) of 0.50% (V_oc = 0.66 V, FF = 0.29) was achieved with PFO‐PTBT (6.5:3.5). © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6175–6184, 2008     

Synthesis of new polyfluorene copolymers with a comonomer containing triphenylamine units and their applications in white‐light‐emitting diodes

Novel conjugated polyfluorene copolymers, poly[9,9‐dihexylfluorene‐2,7‐diyl‐co‐(2,5‐bis(4′‐diphenylaminostyryl)‐phenylene‐1,4‐diyl)]s (PGs), have been synthesized by nickel(0)‐mediated polymerization from 2,7‐dibromo‐9,9‐dihexylfluorene and 1,4′‐dibromo‐2,5‐bis(4‐diphenylaminostyryl)benzene with various molar ratios of the monomers. Because of the incorporation of triphenylamine (TPA) moieties, PGs exhibit much higher HOMO levels than the corresponding polyfluorene homopolymers and are able to facilitate hole injection into the polymer layer from the anode electrode in light‐emitting diodes. Conventional polymeric light‐emitting devices with the configuration ITO/PEDOT:PSS/polymer/Ca/Al have been fabricated. A light‐emitting device produced with one of the PG copolymers (PG10) as the emitting layer exhibited a voltage‐independent and stable bluish‐green emission with color coordinates of (0.22, 0.42) at 5 V. The maximum brightness and current efficiency of the PG10 device were 3370 cd/m² (at 9.6 V) and 0.6 cd/A, respectively. To realize a white polymeric light‐emitting diode, PG10 as the host material was blended with 1.0 wt % of a red‐light‐emitting polymer, poly[9,9‐dioctylfluorene‐2,7‐diyl‐alt‐2,5‐bis(2‐thienyl‐2‐cyanovinyl)‐1‐(2′‐ethylhexyloxy)‐4‐methoxybenzene‐5′,5′‐diyl] (PFR4‐S), and poly[2‐methoxy‐5‐(2′‐ethylhexyloxy)‐1,4‐phenylenevinylene] (MEH‐PPV). The device based on PG10:PFR4‐S showed an almost perfect pure white electroluminescence emission, with Commission Internationale de l'Eclairage (CIE) coordinates of (0.33, 0.36) at 8 V; for the PG10:MEH‐PPV device, the CIE coordinates at this voltage were (0.30, 0.40) with a maximum brightness of 1930 cd/m². Moreover, the white‐light emission from the PG10:PFR4‐S device was stable even at different driving voltages and had CIE coordinates of (0.34, 0.36) at 6 V and (0.31, 0.35) at 10 V. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1199–1209, 2007     

Synthesis and Photovoltaic Properties of Thieno[3,4‐c]pyrrole‐4,6‐dione‐based donor–acceptor Copolymers

Three donor–acceptor (D–A) 1,3‐di(thien‐2‐yl)thieno [3,4‐c]pyrrole‐4,6‐dione‐based copolymers, poly{9,9‐dioctylfluorene‐2,7‐diyl‐alt‐1,3‐bis(4‐hexylthien‐2‐yl)‐5‐octylthieno[3,4‐c]pyrrole‐4,6‐dione}, poly{N‐(1‐octylnonyl)carbazole‐2,7‐diyl‐alt‐1,3‐bis(4‐hexylthien‐2‐yl)‐5‐octylthieno[3,4‐c]pyrrole‐4,6‐dione}, and poly {4,8‐bis(2‐ethylhexyloxyl) benzo[1,2‐b:3,4‐b′]dithiophene‐alt‐1,3‐bis(4‐hexylthien‐2‐yl)‐5‐octylthieno[3,4‐c] pyrrole‐4,6‐dione} were synthesized by Suzuki or Stille coupling reaction. By changing the donor segment, the bandgaps and energy levels of these copolymers could be finely tuned. Cyclic voltammetric study shows that the highest occupied molecular orbital (HOMO) energy levels of the three copolymers are deep‐lying, which implies that these copolymers have good stability in the air and the relatively low HOMO energy level assures a higher open‐circuit potential when they are used in photovoltaic cells. Bulk‐heterojunction photovoltaic cells were fabricated with these polymers as the donors and PC₇₁BM as the acceptor. The cells based on the three copolymers exhibited power conversion efficiencies of 0.22, 0.74, and 3.11% with large open‐circuit potential of 1.01, 0.99, and 0.90 V under one sun of AM 1.5 solar simulator illumination (100 mW/cm²). © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Light‐emitting copolymers based on fluorene and selenophene—Comparative studies with its sulfur analogue: Poly(fluorene‐co‐thiophene)

A series of soluble conjugated copolymers derived from 9,9‐dioctylfluorene (FO) and selenophene (SeH) was synthesized by a palladium‐catalyzed Suzuki coupling reaction with various feed ratios of SeH to FO less than or equal to 50%. The efficient energy transfer from fluorene segments to narrow band‐gap selenophene sites was observed. In comparison with the very well studied copolymer poly(fluorene‐co‐thiophene), poly(9,9‐dioctylfluorene‐co‐selenophene) (PFO‐SeH) shows redshifted photoluminescence (PL) and electroluminescence (EL) emission. PL spectra of the PFO‐SeH copolymers show a significant redshift along with increasing selenophene content in the copolymers and also with increasing polymer concentration in solution. PL quantum efficiency of the selenophene‐containing PFO copolymer is much lower than that of corresponding PFO‐thiophene (Th) copolymers. All these features of PFO‐SeH copolymers can be explained by the difference in aromaticity of selenophene and thiophene heterocycles and the heavy atom effect of Se in comparison with S‐atoms. The device fabricated with PFO‐SeH15 as the emissive layer exhibited high external quantum efficiency (0.51%) at a luminance of 1570 cd/m². Device performance is limited by electron injection and the strong quenching effect of Se atoms. Devices with PFO‐SeH copolymers blended into PFO homopolymers show significant improvement in device performance. External quantum efficiency as high as 1.7% can be obtained for PFO‐SeH30/PFO blend devices. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 823–836, 2005     

Phenothiazine‐S,S‐dioxide‐ and fluorene‐based light‐emitting polymers: Introduction of e−‐deficient S,S‐dioxide into e−‐rich phenothiazine

A novel series of poly(10‐hexyl‐phenothiazine‐S,S‐dioxide‐3,7‐diyl) and poly(9,9′‐dioctyl‐fluorene‐2,7‐diyl‐alt‐10‐hexyl‐3,7‐phenothiazine‐S,S‐dioxide) (PFPTZ‐SS) compounds were synthesized through Ni(0)‐mediated Yamamoto polymerization and Pd(II)‐catalyzed Suzuki polymerization. The synthesized polymers were characterized by ¹H NMR spectroscopy and elemental analysis and showed higher glass transition temperatures than that of pristine polyfluorene. In terms of photoluminescence (PL), the PFPTZ‐SS compounds were highly fluorescent with bright blue emissions in the solid state. Light‐emitting devices were fabricated with these polymers in an indium tin oxide/poly(3,4‐ethylene dioxythiophene):poly(styrene sulfonate)/polymer/Ca/Al configuration. The electroluminescence (EL) of the copolymers differed from the PL characteristics: the EL device exhibited a redshifted greenish‐blue emission in contrast to the blue emission observed in the PL. Additionally, this unique phenothiazine‐S,S‐dioxide property, triggered by the introduction of an electron‐deficient SO₂ unit into the electron‐rich phenothiazine, gave rise to improvements in the brightness, maximum luminescence intensity, and quantum efficiency of the EL devices fabricated with PFPTZ‐SS. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1236–1246, 2007     

Synthesis of novel π‐conjugating polymers based on dibenzothiophene

Novel π‐conjugating polymers based on dibenzothiophene were synthesized with a novel dibenzothiophene derivative, 2,8‐bis(4,4,5,5‐tetramethyl‐1,3,2‐dioxaborolan‐2‐yl)dibenzothiophene ( 1 ), prepared from dibenzothiophene. The Suzuki coupling polycondensation of 1 with 2,7‐dibromo‐9,9‐dioctylfluorene, 3,6‐dibromo‐9‐octylcarbazole, or 1,4‐dibromo‐2,5‐dioctyloxybenzene afforded the corresponding dibenzothiophene‐based polymers. The measurements of photoluminescence indicated that all these polymers exhibited blue emission in solution. The copolymer containing dibenzothiophene and 9,9‐dioctylfluorene units exhibited higher thermal stability than poly[(9,9‐dioctylfluorene‐2,7‐diyl)], although the quantum yield of copolymer was lower than that of poly[(9,9‐dioctylfluorene‐2,7‐diyl)]. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1521–1526, 2003     

Simple synthesis,photophysics, and electroluminescent properties of poly[2,7‐bis(4‐tert‐butylstyryl)fluorene‐9, 9‐diyl‐alt‐alkane‐α,ω‐diyl]

A simple synthetic route was used for the synthesis of a novel series of alternating copolymers based on substituted 2,7‐distyrylfluorene bridged through alkylene chains. First, 2,7‐dibromofluorene was reacted with 2 equiv of butyllithium, and this was followed by a treatment with 1 equiv of α,ω‐dibromoalkane to yield the intermediate, poly(2,7‐dibromofluorene‐9,9‐diyl‐alt‐alkane‐α,ω‐diyl). ( 1 ) Heck coupling of the latter with 1‐tert‐butyl‐4‐vinylbenzene afforded the target, poly[2,7‐bis(4‐tert‐butylstyryl)fluorene‐9,9‐diyl‐alt‐alkane‐α,ω‐diyl] ( 2 ). The two versions of 2 ( 2a and 2b which have hexane and decane, respectively, as alkane groups) were readily soluble in common organic solvents. Their glass‐transition temperature was relatively low (52 and 87 °C). An intense blue photoluminescence emission with maxima at about 408 and 409 nm was observed in tetrahydrofuran solutions, whereas thin films exhibited an orange emission with maxima at 569 and 588 nm. Very large redshifts of the photoluminescence maxima and Stokes shifts in thin films indicated strong aggregation in the solid state. Both polymers oxidized and reduced irreversibly. Single‐layer light‐emitting diodes with hole‐injecting indium tin oxide and electron‐injecting aluminum electrodes were fabricated. They emitted orange light with external electroluminescence efficiencies of 0.52 and 0.36% photon/electron, as determined in light‐emitting diodes made of 2a and 2b , with alkylenes of (CH₂)₆ and (CH₂)₁₀, respectively. An increase in the external electroluminescence efficiency up to 1.5% was reached in light‐emitting diodes made of polymer blends consisting of 2a and poly(9,9‐dihexadecylfluorene‐2,7‐diyl), which emitted blue‐white light. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 809–821, 2007.     

Synthesis and electroluminescent properties of fluorene‐based copolymers containing electron‐withdrawing thiazole derivatives

We synthesized two fluorene‐based copolymers poly[(2,5‐bis(4‐hexylthiophen‐2‐yl)thiazolo[5,4‐day]thiazole‐5,5′‐diyl)‐alt‐(9,9′‐dioctylfluorene‐2,7‐diyl)] ( PF‐TTZT), and poly[(5,5′‐bis(4‐hexylthiophen‐2‐yl)‐2,2′‐bithiazole‐5,5′‐diyl)‐alt‐(9,9′‐dioctylfluorene‐2,7‐diyl)] (PF‐TBTT), which contain the electron‐withdrawing moieties, thiazolothiazole, and bithiazole, respectively. Through electrochemical studies, we found that these two polymers exhibit stable reversible oxidation and reduction behaviors. Moreover, the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of PF‐TBTT are lower than those of PF‐TTZT, and the bandgap of PF‐TBTT is smaller than that of PF‐TTZT. Thus the bithiazole moiety in PF‐TBTT is more electron‐withdrawing than the thiazolothiazole moiety in PF‐TTZT. Light‐emitting devices with indium tin oxide (ITO)/poly(3,4‐ethylene dioxythiophene):poly(styrenesulfonate)(PEDOT)/polymer/bis(2‐methyl‐8‐quinolinato)‐4‐phenylphenolate aluminum (BAlq)/LiF/Al configurations were fabricated. The performance of the PF‐TBTT device was found to be almost three times better than that of the PF‐TTZT device, which is because electron injection from the cathode to PF‐TBTT is much easier than for PF‐TTZT. We also investigated the planarity and frontier orbitals of the electron donor‐acceptor (D‐A) moieties with computational calculations using ab initio Hartree–Fock with the split‐valence 6‐31G* basis set. These calculations show that TBTT has a more nonplanar structure than TTZT and that the bithiazole moiety is more electron‐withdrawing than thiazolothiazole. These calculations are in good agreement with the experimental results. © Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7148–7161, 2008     

Synthesis and characterization of fluorene‐based copolymers containing benzothiadiazole derivative for light‐emitting diodes applications

Five new thermally robust electroluminescent fluorene‐based conjugated copolymers, including poly[2,7‐(9,9‐dioctylfluorene)‐co‐4,7‐{5,6‐bis(3,7‐dimethyloctyloxymethyl)‐2,1,3‐(benzothiadiazole)}] ( PFO‐P2C₁₀BT ) were synthesized and used to fabricate the efficient polymer light‐emitting diodes (PLEDs). The glass transition temperatures of the polymers were found to be higher than that of poly(9,9‐dialkylfluorenes) and are in the range 113–165 °C. We fabricated PLEDs in indium‐tin oxide/PEDOT/light‐emitting polymer/cathode configurations using either double‐layer LiF/Al or triple‐layer Alq₃/LiF/Al cathode structures. The new copolymers were found to have emission colors that vary from greenish blue (491 nm) to green (543 nm) depending on the copolymer composition. The maximum brightness and luminance efficiency of these PLEDs were found to be up to 5347 cd/m² and 1.51 cd/A at 10 V, respectively. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6762–6769, 2008     

White light electroluminescence from graphene‐enhanced single polymer comprising two color emitters of equal molar ratios

White polymeric light‐emitting diode (WPLED) based on a single polymer, poly(3‐hexylthiophene‐alt‐9,9‐dioctylfluorene) (PTAF), has been successfully demonstrated. This conjugated alternating copolymer, PTAF, comprises 50 mol % of 3‐hexylthiophene which is an orange‐red color chromophore and 50 mol % 9,9‐dioctylfluorene which is a bluish‐green color chromophore. It was synthesized by Suzuki cross‐coupling reaction and has a molecular weight of 15,021 and polydispersity of 1.36. Nanocomposite consisting PTAF and graphene nanosheets enhances the optoelectronic properties and the device fabricated with a configuration of ITO/PEDOT:PSS/(PTAF + 1% graphene)/Ca/Al shows two‐color white electroluminescence with CIE 1931 coordinates of (0.28, 0.34). The white luminescence from a single polymer affords the WPLED device a simple structure and low fabrication cost. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Significantly improved photovoltaic performances of the dithiophene‐benzothiadiazole‐alt‐fluorene copolymers by incorporating carbazole units in fluorene moiety

To exploit an effective way to improve polymeric photovoltaic performance, a series of dithiophene‐benzothiadiazole‐alt‐fluorene copolymers containing carbazole groups at C‐9 positions of the alternating fluorene units (PFO‐FCz‐DBT) were synthesized and characterized. The effect of the carbazole groups on the optophysical, electrochemical, and photovoltaic properties of these copolymers was investigated. By comparison, this type of copolymers with carbazole units exhibited significantly improved photovoltaic properties than poly(2,7‐(9,9‐dioctyl‐fluorene)‐alt‐5,5‐(4′,7′‐di‐2‐thienyl‐2′,1′,3′‐benzothiadiazole) (PFO‐DBT) in the bulk heterojunction solar cells. A maximum power‐conversion efficiency (PCE) of 2.41% and a highest short‐circuit current density (J_sc) of 9.68 mA cm^?2 were obtained for the PFO‐FCz‐DBT30, which are about two times higher than the corresponding levels for the PFO‐DBT30. This work demonstrated that introducing a hole‐transporting carbazole unit into copolymer is a simple and effective method to improve the J_sc and PCE. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Photovoltaic performance enhancement using fluorene‐based copolymers containing pyrene units

A set of novel conjugated polyfluorene co‐ polymers, poly[(9,9′‐didecylfluorene‐2,7‐diyl)‐co‐(4,7′‐di‐2‐thienyl‐ 2′,1′,3′‐benzothiadiazole‐5,5‐diyl)‐co‐(pyrene‐1,6‐diyl)], are synthesized via Pd(II)‐mediated polymerization from 2,7‐bis(4′,4′,5′, 5′‐tetramethyl‐1,3,2‐dioxaborolan‐2‐yl)‐9,9′‐di‐n‐decylfluorene, 4, 7‐di(2‐bromothien‐5‐yl)‐2,1,3‐benzothiadiazole, and 1,6‐dibromopyrene with a variety of monomer molar ratios. The field‐effect carrier mobilities and optical, electrochemical, and photovoltaic properties of the copolymers are systematically investigated. The hole mobilities of the copolymers are found to be in the range 7.0 × 10^?5 ? 8.0 × 10^?4 cm² V^?1 s^?1 and the on/off ratios were 8 × 10³ ? 7 × 10⁴. Conventional polymer solar cells (PSCs) with the configuration ITO/PEDOT:PSS/polymer:PC₇₁BM/LiF/Al are fabricated. Under optimized conditions, the polymers display power conversion efficiencies (PCEs) for the PSCs in the range 1.99–3.37% under AM 1.5 illumination (100 mW cm^?2). Among the four copolymers, P2, containing a 2.5 mol % pyrene component incorporated into poly[9,9′‐didecylfluorene‐alt‐5,5‐(4′,7′‐di‐2‐thienyl‐2′,1′,3′‐benzothiadiazole)] (PFDTBT) displays a PCE of 3.37% with a short circuit current of 9.15 mA cm^?2, an open circuit voltage of 0.86 V, and a fill factor of 0.43, under AM 1.5 illumination (100 mW cm^?2). © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Thermally crosslinkable hole‐transporting poly(fluorene‐co‐triphenylamine) for multilayer polymer light‐emitting diodes

This article reports the synthesis and characterization of a novel thermally crosslinkable hole‐transporting poly (fluorene‐co‐triphenylamine) (PFO‐TPA) by Suzuki coupling reaction, followed with its application in the fabrication of multilayer light‐emitting diodes by wet processes. The thermal, photophysical, and electrochemical properties of PFO‐TPA were investigated by differential scanning calorimeter, thermogravimetric analysis, optical spectroscopy, and cyclic voltammetry, respectively. Thermally crosslinked PFO‐TPA, through pendant styryl groups, demonstrates excellent thermal stability (T_d > 400 °C, T_g = 152 °C), solvent resistance, and film homogeneity. Its highest occupied molecular orbital level (?5.30 eV) lies between those of PEDOT:PSS (?5.0 ～ ?5.2 eV) and poly(9,9‐dioctylfluorene) (PFO: ?5.70 eV), forming a stepwise energy ladder to facilitate hole injection. Multilayer device with crosslinked PFO‐TPA as hole‐injection layer (HIL) (ITO/PEDOT:PSS/HIL/PFO/LiF/Ca/Al) was readily fabricated by successive spin‐coating processes, its maximum luminance efficiency (3.16 cd/A) were about six times higher than those without PFO‐TPA layer (0.50 cd/A). The result of hole‐only device also confirmed hole‐injection and hole‐transport abilities of crosslinked PFO‐TPA layer. Consequently, the device performance enhancement is attributed to more balanced charges injection in the presence of crosslinked PFO‐TPA layer. The thermally crosslinkable PFO‐TPA is a promising material for the fabrication of efficient multilayer polymer light‐emitting diodes because it is not only a hole‐transporting polymer but also thermally crosslinkable. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis and characterization of new π‐conjugated polymers containing 1,8‐naphthyridine in the main chain: Role of the 1,8‐naphthyridine unit in π‐conjugated polymers

Alternating π‐conjugated copolymers of 1,8‐naphthyridine‐2,6‐diyl ( 1,8‐Nap ) with 9,9‐dioctylfluorene‐2,7‐diyl ( P(Flu‐Ph‐1,8‐Nap) ) and 2,5‐didodecyloxy‐1,4‐phenylene ( P(ROPh‐Ph‐1,8‐Nap) ) have been synthesized by Pd‐catalyzed organometallic polycondensation. The copolymers showed UV‐vis absorption peaks at around 390 nm in o‐dichlorobenzene. The polymers were photoluminescent both in o‐dichlorobenzene and in the solid state. In o‐dichlorobenzene, the emission peaks of P(Flu‐Ph‐1,8‐Nap) and P(ROPh‐Ph‐1.,8‐Nap) appeared at λ_EM = 440 and 471 nm, with quantum yields of 87% and 66%, respectively. Electrochemical data revealed that 1,8‐Nap behaved as a typical electron‐accepting unit. When P(Flu‐Ph‐1,8‐Nap) was treated with 10‐camphorsulfonic acid, the emission peak shifted to λ_EM = 598 nm. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

New blue electroluminescent n‐type polyfluorene copolymers with a 1,3,4‐oxadiazole unit in the main chain

Novel polyfluorene copolymers alternately having an 1,3,4‐oxadiazole unit in the main chain were prepared by both one‐step and two‐step methods for polyoxadiazole synthesis. They displayed highly efficient blue photoluminescence, the properties of which were affected by the extent of conjugation and the changes in the electron density by a side chain. An electrochemical analysis of the polymers using cyclic voltammetry suggested that they could be used as electron‐transport/hole‐blocking materials as well as blue emission materials for polymer light‐emitting diodes. A simple double‐layer device consisting of poly(N‐vinylcarbazole) as a hole‐transport layer and poly[(9,9′‐didodecylfluorene‐2,7‐diyl)‐alt‐((1,4‐bis(1,3,4‐oxadiazole)‐2,5‐di(2‐ethylhexyloxy)phenylene)‐5,5′‐diyl)] as an emission layer exhibited narrow blue electroluminescence with a maximum at 430 nm. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1058–1068, 2004     

Synthesis of three new 1‐(2,6‐diisopropylphenyl)‐2,5‐di(2‐thienyl) pyrrole‐based donor polymers and their bulk heterojunction solar cell applications

A series of three new 1‐(2,6‐diisopropylphenyl)‐2,5‐di(2‐thienyl)pyrrole‐based polymers such as poly[1‐(2,6‐diisopropylphenyl)‐2,5‐di(2‐thienyl)pyrrole] ( PTPT ), poly[1,4‐(2,5‐bis(octyloxy)phenylene)‐alt‐5,5'‐(1‐(2,6‐diisopropylphenyl)‐2,5‐di(2‐thienyl)pyrrole)] ( PPTPT ), and poly[2,5‐(3‐octylthiophene)‐alt‐5,5'‐(1‐(2,6‐diisopropylphenyl)‐2,5‐di(2‐thienyl)pyrrole)] ( PTTPT ) were synthesized and characterized. The new polymers were readily soluble in common organic solvents and the thermogravimetric analysis showed that the three polymers are thermally stable with the 5% degradation temperature >379 °C. The absorption maxima of the polymers were 478, 483, and 485 nm in thin film and the optical band gaps calculated from the onset wavelength of the optical absorption were 2.15, 2.20, and 2.13 eV, respectively. Each of the polymers was investigated as an electron donor blending with PC₇₀BM as an electron acceptor in bulk heterojunction (BHJ) solar cells. BHJ solar cells were fabricated in ITO/PEDOT:PSS/polymer:PC₇₀BM/TiO_x/Al configurations. The BHJ solar cell with PPTPT :PC₇₀BM (1:5 wt %) showed the power conversion efficiency (PCE) of 1.35% (J_sc = 7.41 mA/cm², V_oc = 0.56 V, FF = 33%), measured using AM 1.5G solar simulator at 100 mW/cm² light illumination. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

High‐efficiency,electrophosphorescent polymers with porphyrin–platinum complexes in the conjugated backbone: Synthesis and device performance

A series of soluble, conjugated, electrophosphorescent copolymers with (meso‐tetraphenylporphyrinato‐κ⁴N)platinum(II) (PtTPP) complexes incorporated into the polymer main chain were synthesized through the copolymerization of narrow‐band‐gap monomeric porphyrin–platinum(II) complexes and wide‐band‐gap dialkyl‐substituted fluorene monomers by a modified Suzuki coupling reaction. The study of the photoluminescence decay indicated that poly[2,7‐(9,9‐dioctylfluorene)‐co‐2,12‐((meso‐tetraphenylporphyrinato‐κ⁴N)platinum(II))] (PFO–PtTPP) was a triplet emitter. The electroluminescence emission from the fluorene segment was completely quenched for copolymers with PtTPP contents as low as 0.5 mol %. The PFO–PtTPP copolymers emitted deep red light. The device based on the porphyrin–platinum(II) copolymer PFO–5PtTPP (with 5 mol % PtTPP in the copolymer) showed the highest external quantum efficiency of 1.95% with an emission peak at 684 nm in an indium tin oxide/poly(3,4‐ethylenedioxythiophene)/polyvinylcarbazole (PVK)/70:30 (w/w) PFO–5PtTPP: 2‐(biphenyl‐4‐yl)‐5‐(4‐tert‐butylphenyl)‐1,3,4‐oxadiazole/Ba/Al device configuration. In comparison with the PFO–PtTPP copolymers synthesized via a postpolymerization metalation route, copolymerization from Pt metal complexes proved to be a more efficient synthetic route for high‐efficiency electrophosphorescent polymers. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4174–4186, 2006