Supramolecular assembly of H‐bonded side‐chain polymers containing conjugated pyridyl H‐acceptor pendants and various low‐band‐gap H‐donor dyes bearing cyanoacrylic acid groups for organic solar cell applications

Novel supramolecular side‐chain polymers were constructed by complexation of proton acceptor (H‐acceptor) polymers, i.e., side‐chain conjugated polymers P1–P2 containing pyridyl pendants, with low‐band‐gap proton donor (H‐donor) dyes S1–S4 (bearing terminal cyanoacrylic acids) in a proper molar ratio. Besides unique mesomorphic properties confirmed by DSC and XRD results, the H‐bonds of supramolecular side‐chain structures formed by pyridyl H‐acceptors and cyanoacrylic acid H‐donors were also confirmed by FTIR measurements. H‐donor dyes S1–S4 in solid films exhibited broad absorption peaks located in the range of 471–490 nm with optical band‐gaps of 1.99–2.14 eV. Furthermore, H‐bonded polymer complexes P1/S1–P1/S4 and P2/S1–P2/S4 exhibited broad absorption peaks in the range of 440–462 nm with optical band‐gaps of 2.11–2.25 eV. Under 100 mW/cm² of AM 1.5 white‐light illumination, the bulk heterojunction polymer solar cell (PSC) devices containing an active layer of H‐bonded polymer complexes P1/S1–P1/S4 and P2/S1–P2/S4 (as electron donors) mixed with [6,6]‐phenyl C₆₁ butyric acid methyl ester (i.e., PCBM, as an electron acceptor) in the weight ratio of 1:1 were investigated. The PSC device containing H‐bonded polymer complex P1/S3 mixed with PCBM (1:1 w/w) gave the best preliminary result with an overall power conversion efficiency (PCE) of 0.50%, a short‐circuit current of 3.17 mA/cm², an open‐circuit voltage of 0.47 V, and a fill factor of 34%. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5998–6013, 2009     

Novel narrow‐band‐gap conjugated copolymers containing phenothiazine‐arylcyanovinyl units for organic photovoltaic cell applications

A series of novel narrow‐band‐gap copolymers ( P1 ‐ P12 ) composed of alkyl‐substituted fluorene (FO) units and six analogous mono‐ and bis(2‐aryl‐2‐cyanovinyl)‐10‐hexylphenothiazine monomers ( M1 ‐ M6 ) were synthesized by a palladium‐catalyzed Suzuki coupling reaction with two different feed in ratios of FO to M1 ‐ M6 (molar ratio = 3:1 and 1:1). The absorption spectra of polymers P1 ‐ P12 exhibited broad peaks located in the UV and visible regions from 400 to 800 nm with optical band gaps at 1.55–2.10 eV, which fit near the wavelength of the maximum solar photon reflux. Electrochemical experiments displayed that the reversible p‐ and n‐doping processes of copolymers were partially reversible, and the proper HOMO/LUMO levels enabled a high photovoltaic open‐circuit voltage. As blended with [6,6]‐phenyl C₆₁ butyric acid methyl ester (PCBM) as an electron acceptor in bulk heterojunction photovoltaic devices, narrow‐band‐gap polymers P1 ‐ P12 as electron donors showed significant photovoltaic performance which varied with the intramolecular donor‐acceptor interaction and their mixing ratios to PCBM. Under 100 mW/cm² of AM 1.5 white‐light illumination, the device of copolymer P12 produced the highest preliminary result having an open‐circuit voltage of 0.64 V, a short‐circuit current of 2.70 mA/cm², a fill factor of 0.29, and an energy conversion efficiency of 0.51%. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4285–4304, 2008     

Synthesis and characterization of arylenevinylenearylene–naphthalene diimide copolymers as acceptor in all–polymer solar cells

Two n‐type conjugated D‐A copolymers, P(TVT‐NDI) and P(FVF‐NDI) with thienylene‐vinylene‐thienylene (TVT) or furanylene‐vinylene‐furanylene (FVF) as donor (D) units and naphthalene diimide (NDI) as the acceptor (A) units, were synthesized by the Stille coupling copolymerization. The two polymers possess good solubility, high thermal stability, and broad absorption bands with absorption edges at 866 nm for P(TVT‐NDI) and 886 nm for P(FVF‐NDI) . The LUMO energy levels of P(TVT‐NDI) and P(FVF‐NDI) are ?3.80 eV and ?3.76 eV respectively, so the two polymers are suitable for the application as acceptor in blending with most polymer donor in PSCs based on the energy level matching point of view. All polymer solar cells (all‐PSCs) were fabricated with P(TVT‐NDI) or P(FVF‐NDI) as acceptor and medium bandgap polymer J51 as donor for investigating the photovoltaic performance of the two n‐type conjugated polymer acceptors. And higher power conversion efficiency of 6.43% for P(TVT‐NDI) and 5.21% for P(FVF‐NDI) was obtained. The results indicate that arylenevinylenearylene–naphthalene diimide copolymer are promising polymer acceptor for all–PSCs. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 1757–1764     

Narrow band gap D–A copolymer of indacenodithiophene and diketopyrrolopyrrole with deep HOMO level: Synthesis and application in field‐effect transistors and polymer solar cells

A novel fused ladder alternating D–A copolymer, PIDT–DPP, with alkyl substituted indacenodithiophene (IDT) as donor unit and diketopyrrolopyrrole (DPP) as acceptor unit, was designed and synthesized by Pd‐catalyzed Stille‐coupling method. The copolymer showed good solubility and film‐forming ability combining with good thermal stability. PIDT–DPP exhibited a broad absorption band from 350 to 900 nm with an absorption peak centered at 735 nm. The optical band gap determined from the onset of absorption of the polymer film was 1.37 eV. The highest occupied molecular orbital level of the polymer is as deep as ?5.32 eV. The solution‐processed organic field‐effect transistor (OFETs) was fabricated with bottom gate/top contact geometry. The highest FET hole mobility of PIDT–DPP reached 0.065 cm² V^?1 s^?1 with an on/off ratio of 4.6 × 10⁵. This mobility is one of the highest values for narrow band gap conjugated polymers. The power conversion efficiency of the polymer solar cell based on the polymer as donor was 1.76% with a high open circuit voltage of 0.88 V. To the best of our knowledge, this is the first report on the photovoltaic properties of alkyl substituted IDT‐based polymers. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

An acceptor‐acceptor conjugated copolymer based on perylene diimide for high mobility n‐channel transistor in air

A new solution‐processable acceptor‐acceptor conjugated copolymer ( P1 ) based on perylene diimide (PDI) incorporating planar electron‐deficient fluorenone was synthesized by palladium(0)‐catalyzed Suzuki coupling reaction. Relative to the donor‐acceptor conjugated copolymer ( P2 ) of PDI and dithienothiophene, polymer P1 exhibits 0.1 eV down shift of lowest unoccupied molecular orbital (LUMO) level, 70 nm blue shift of low‐energy absorption band, and 0.36 eV increase of optical band gap. Polymer P1 in top‐contact bottom‐gate organic field‐effect transistors exhibits a saturation electron mobility of 0.01 cm²/(V s) in air, while P2 does not function in the same device in air. The better air stability of P1 is attributed to a more dense packing of the polymer chains excluding oxygen or water and lower LUMO level of P1 . © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Bandgap engineering of indenofluorene‐based conjugated copolymers with pendant donor‐π‐acceptor chromophores for photovoltaic applications

Three narrow‐band‐gap conjugated copolymers based on indenofluorene and triphenylamine with pendant donor‐π‐acceptor chromophores were successfully synthesized by post‐functionalization approach. All the polymers have good solubility in common solvents and excellent thermal stability. The photophysical properties, energy levels and band gaps of the polymers were well manipulated by introducing different acceptor groups onto the end of their conjugated side chains. By using different acceptor groups, the band gaps of the polymers were narrowed from 1.86 to 1.53 eV by lowering their lowest unoccupied molecular orbital levels, whereas their relatively deep highest occupied molecular orbital levels of approximately ?5.35 eV were maintained. Bulk‐heterojunction solar cells with these polymers as electron donors and (6,6)‐phenyl‐C₇₁‐butyric acid methyl ester as acceptor showed power conversion efficiencies as high as 3.1% and high open circuit voltages more than 0.88 eV. The relationships between the performance and film morphology, energy levels, charge mobilities were discussed. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis and characterization of highly conjugated side‐group‐substituted benzo[1,2‐b:4,5‐b′]dithiophene‐based copolymer for use in organic solar cells

A new donor–acceptor (D–A) conjugated copolymer based on benzo[1,2‐b:4,5‐b′]dithiophene (BDT) and thieno[3,4‐c]pyrrole‐4,6‐dione (TPD) was synthesized via a Stille cross‐coupling reaction. A highly conjugated thiophene‐based side group, tris(thienylenevinylene) (TTV), was incorporated into each BDT unit to generate the two‐dimensional D–A copolymer (PBDT‐TTV). An alkoxy‐substituted BDT‐based TPD copolymer (PBDT‐OR) was synthesized using the same polymerization method for comparison. PBDT‐TTV thin films produced two distinct absorption peaks. The shorter wavelength absorption (458 nm) was attributed to the BDT units containing the TTV group, and the longer wavelength band (567–616 nm) was attributed to intramolecular charge transfer between the BDT donor and the TPD acceptor. The highest occupied molecular orbital energy levels of PBDT‐OR and PBDT‐TTV were calculated to be −5.53 and −5.61 eV, respectively. PBDT‐TTV thin films harvested a broad solar spectrum covering the range 300–700 nm. A comparison with the PBDT‐OR films revealed stronger interchain π–π interactions in the PBDT‐TTV films and, thus, a higher hole mobility. A polymer solar cell device prepared using PBDT‐TTV as the active layer was found to exhibit a higher power conversion efficiency than a device prepared using PBDT‐OR under AM 1.5 G (100 mW/cm²) conditions. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 653–660     

Synthesis and photovoltaic properties of two‐dimensional D‐A copolymers with conjugated side chains

Four novel two‐dimensional (2D) donor–acceptor (D‐A) type copolymers with different conjugated side chains, P1 , P2 , P3 , and P4 (see Fig. 1 ), are designed and synthesized for the application as donor materials in polymer solar cells (PSCs). To the best of our knowledge, there were few reports to systematically study such 2D polymers with D‐A type main chains in this area. The optical energy band gaps are about 2.0 eV for P1 – P3 and 1.67 eV for P4 . PSC devices using P1 – P4 as donor and [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester as acceptor in a weight ratio of 1:3 were fabricated and characterized to investigate the photovoltaic properties of the polymers. Under AM 1.5 G, 100 mA/cm² illumination, a high open‐circuit voltage (V_oc) of 0.9 V was recorded for P3 ‐based device due to its low HOMO level, and moderate fill factor was obtained with the best value of 58.6% for P4 ‐based device, which may mainly be the result of the high hole mobility of the polymers (up to 1.82 × 10^?3 cm²/V s). © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis and characterization of new sulfone‐derivatized phenylenevinylene‐based conjugated copolymers with evolving energy levels and gaps

A new series of stable, processable, and chain end functionalizable sulfone‐derivatized phenylenevinylene‐based conjugated polymers (SFPVs) containing different donor type comonomers have been synthesized and characterized. The polymer main chains are consisted of a sulfone‐phenylene electron accepting unit coupled with an electron donating unit which is derived from one of the dialdehyde comonomers based on benzene, thiophene, and pyrrole (with or without alkoxy side chains). The optical energy gaps (E_g) of the new polymers (in solvent) are in a range of 1.9–2.3 eV, with the lowest energy gap obtained from the polymer containing pyrrole as the donor unit. By using a combination of strong donor unit (such as pyrrole) and a relatively weak but stable acceptor unit (sulfone‐substituted benzene), E_g of the conjugated polymers can be tailored to below 2 eV, while the vinylene bonds on the polymer main chain are still chemically stable to survive strong basic conditions as compared with the S,S‐dioxo‐thiophene‐based PTV polymers developed earlier for potential supra‐molecular block copolymer systems. The lowest energy gap P(Pyrrole‐SFPV) exhibited 10 times better photoelectric power conversion efficiency than P(TV‐SFPV). © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Tropone‐containing π‐conjugated polymers: Annulation of tropone onto benzene ring in the conjugated polymer

Tropone‐fused, various π‐conjugated polymers ( P2 – P5 ) were synthesized by the palladium‐catalyzed coupling reaction of 1,4‐dibromo‐6,8‐dimethyl‐7H‐benzocyclohepten‐7‐one with aromatic divinyl, diboronic acid, and diethynyl compounds. The molecular orbital calculation of the model compounds was performed to discuss effective conjugation length of the repeating unit of the polymers. The absorption spectra of phenylenevinylene‐type polymers shifted to longer wavelengths than the model compounds by about 60 nm. They exhibited green fluorescence [λ_max(em) = 544 and 561 nm]. The absorption spectrum of a phenylene‐type polymer blueshifted by 10 nm; however, that of a phenyleneethynylene‐type polymer redshifted by 83 nm as compared with their model compounds. They showed fluorescence with peak maxima at 457 and 489 nm, respectively. As a result, the absorption spectra of phenylene‐ and phenylenevinylene‐type polymers blueshifted, but that of a phenyleneethynylene‐type polymer redshifted by the annulation of tropone onto a benzene ring in the conjugated polymer. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1208–1215, 2004     

Conjugated polymers with broad absorption: Synthesis and application in polymer solar cells

A series of main chain donor‐acceptor low‐bandgap conjugated polymers were designed, synthesized, and used for the fabrication of polymer solar cells. The absorption spectra of low‐bandgap conjugated polymers were tuned by the ratio of three copolymerization monomers. The polymers in films exhibited broad absorption ranging from 300 to 1000 nm with optical bandgaps of around 1.40 eV. All of the polymers have been investigated as an electron donor in photovoltaic cells blending with PCBM ([6, 6]‐phenyl C61‐butyric acid methyl ester) as an electron acceptor and power conversion efficiencies (PCEs) of 1.32–1.8% have been obtained. As for P1 , PCE increases from 1.67 to 2.44% after adding 1,8‐diiodooctance as an additive. The higher PCEs are probably because of better phase separation of blend films. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2571–2578, 2010     

Synthesis and characterization of novel low‐bandgap triphenylamine‐based conjugated polymers with main‐chain donors and pendent acceptors for organic photovoltaics

A series of novel low‐bandgap triphenylamine‐based conjugated polymers ( PCAZCN , PPTZCN , and PDTPCN ) consisting of different electron‐rich donor main chains (N‐alkyl‐2,7‐carbazole, phenothiazine, and cyclopentadithinopyrol, respectively) as well as cyano‐ and dicyano‐vinyl electron‐acceptor pendants were synthesized and developed for polymer solar cell applications. The polymers covered broad absorption spectra of 400–800 nm with narrow optical bandgaps ranging 1.66–1.72 eV. The highest occupied molecular orbital and lowest unoccupied molecular orbital levels of the polymers measured by cyclic voltammetry were found in the range of ?5.12 to ?5.32 V and ?3.45 to ?3.55 eV, respectively. Under 100 mW/cm² of AM 1.5 white‐light illumination, bulk heterojunction photovoltaic devices composing of an active layer of electron‐donor polymers ( PCAZCN , PPTZCN , and PDTPCN ) blended with electron‐acceptor [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester or [6,6]‐phenyl‐C₇₁‐butyric acid methyl ester (PC₇₁BM) in different weight ratios were investigated. The photovoltaic device containing donor PCAZCN and acceptor PC₇₁BM in 1:2 weight ratio showed the highest power conversion efficiency of 1.28%, with V_oc = 0.81 V, J_sc = 4.93 mA/cm², and fill factor = 32.1%. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

New moderate bandgap polymers containing alkoxysubstituted‐benzo[c][1,2,5]thiadiazole and thiophene‐based units

Alkoxysubstituted benzo[c][1,2,5]thiadiazole electron accepting units were prepared and copolymerized with various thiophene‐based electron donating monomers to produce new low bandgap polymers P1–4 . The materials showed broad absorption in the range from 300 to 700 nm with bandgaps below 2 eV in solution. Efficiencies of over 1% were obtained from photovoltaic cells using P4 with PCBM as acceptor. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis of polymers containing 1,2,4‐oxadiazole as an electron‐acceptor moiety in their main chain and their solar cell applications

To explore the aptitude of 1,2,4‐oxadiazole‐based electron‐acceptor unit in polymer solar cell applications, we prepared four new polymers (P1–P4) containing 1,2,4‐oxadiazole moiety in their main chain and applied them to solar cell applications. Thermal, optical, and electrochemical properties of the polymers were studied using thermogravimetric, absorption, and cyclic voltammetry analysis, respectively. All four polymers showed high thermal stability (5% degradation temperature over 335 °C), and the optical band gaps were calculated to be 2.20, 1.72, 1.37, and 1.74 eV, respectively, from the onset wavelength of the film‐state absorption band. The energy levels of the polymers were found to be suitable for bulk heterojunction (BHJ) solar cell applications. The BHJ solar cells were prepared by using the synthesized polymers as a donor and PC₇₁BM as an electron acceptor with the configuration of ITO/PEDOT:PSS/polymer:PC₇₁BM (1:3 wt %)/LiF/Al. One of the polymers was found to show the maximum power conversion efficiency of 1.33% with a Jsc of 4.95 mA/cm², a V_oc of 0.68 V, and a FF of 40%, measured using AM 1.5 G solar simulator at 100 mW/cm₂ light illumination. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Control of vertical distribution of thiophene‐based copolymers containing 4,7‐Dithien‐2‐yl‐benzo[C][1,2,5]thiadiazole and 3,6‐Dithien‐2‐yl‐pyrrolo[3,4‐C]pyrrole‐1,4(2H,5H)‐dione as Side Groups for Photovoltaics

Four new D—A type copolymers with 2D‐conjugated side‐chain identified PfToBT, PbToBT, PfTDPP and PbTDPP, containing two acceptors 4,7‐dithien‐2‐yl‐benzo[c][1,2,5]thiadiazole (DTBT), and diketopyrrolopyrrole (DPP) linked by thiophene donors, are obtained using Pd‐catalyzed Stille‐coupling reaction. These polymers show a broad visible‐near‐infrared absorption band (E_g = 1.79–1.66 eV) and possess a relatively low‐lying HOMO level at ?5.34 to ?5.12 eV. All the polymer:PC₇₀BM blend films showed edge‐on structure and have similar d_π‐spacing values. According to the structure of conjugated side‐chain, the vertical distributions of polymer chains and PC₇₀BM within the BHJ (bulk heterojunction) were different. When DPP used as an acceptor, conjugated side chains of the polymer coexisted with PC₇₀BM in same position. The BHJ film prepared from PfToBT, PbToBT had a discontinuous network between polymer and PC₇₀BM, whereas films from PfTDPP and PbTDPP formed continuous and evenly distributed network between them. This optimized vertical morphology promotes hole transport along respective pathways of polymers and fullerenes in the vertical direction, leading to high J_SC. PbTDPP shows PCE up to 2.9% (Jsc of 9.4 mA/cm², Voc of 0.68 V, and FF of 0.44). © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2746–2759     

Synthesis and photovoltaic properties of conjugated side chains polymers with different electron‐withdrawing and donating end groups

A series of novel low band gap polymers containing conjugated side chains with 4,7‐dithien‐5‐yl‐2,1,3‐benzodiathiazole and different electron‐withdrawing end groups of aldehyde ( PT‐DTBTCHO ), 2‐ethylhexyl cyanoacetate ( PT‐DTBTCN ), 1,3‐diethyl‐2‐thiobarbituric acid ( PT‐DTBTDT ), and electron‐donating end group of 2‐methylthiophene ( PT‐DTBTMT ) have been designed and synthesized. All polymers exhibit good solubility in common organic solvents, film‐forming ability, and thermal stability. These conjugated polymers show the broad ultraviolet‐visible absorption and the narrow optical band gaps in the range of 1.65–1.90 eV. Through changing the end group of conjugated side chains, the photophysical properties and energy levels of the polymers were tuned effectively. Bulk heterojunction solar cells based on the blend of these polymers and (6,6)‐phenyl‐C₆₁‐butyric acid methyl ester (PC₆₁BM) reached the best power conversion efficiency (PCE) of 2.72%. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Carbazole‐based conjugated polymers incorporating push/pull organic dyes: Synthesis,characterization, and photovoltaic applications

We have synthesized and characterized two new carbazole‐based conjugated polymers, PCDCN and PCDTA , incorporating two strong light‐absorbing organic dyes. These polymers exhibit relatively low band gaps (～1.5 eV) and broad absorption ranges (from 300 to 700 nm). We fabricated polymer solar cells incorporating these polymers as donors and [6,6]‐phenyl‐C₇₁‐butyric acid methyl ester (PC₇₁BM) as the acceptor. At a blending ratio of 1:4, we obtained power conversion efficiencies, under simulated AM 1.5 (100 mW/cm²) conditions, of 2.31% and 2.47% for the PCDCN ‐ and PCDTA ‐based devices, respectively. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Diketopyrrolopyrrole‐based acceptor–acceptor conjugated polymers: The importance of comonomer on their charge transportation nature

Besides the donor–acceptor (D–A) type, acceptor–acceptor (A–A) polymers are another class of important alternative conjugated copolymers, but have been less studied in the past. In this study, two kinds of A–A polymers, P1 and P2 , have been designed and synthesized based on diketopyrrolopyrrole in combination with the second electron‐deficient unit, perylenediimide or thieno[3,4‐c]pyrrole‐4,6‐dione. UV–vis absorption spectroscopy revealed that these two kinds of polymers have a band gap of 1.28–1.33 eV. Their highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels are around ?5.6 and ?4.0 eV for P1 polymers, whereas ?5.4 and ?3.7 eV for P2 polymers, respectively. Density functional theory study disclosed that P1 backbone is in a vastly twisting state, whereas that of P2 is completely planar. Furthermore, organic field‐effect transistor devices were fabricated using these two kinds of polymers as the active material. Of interest, the devices based on P1 polymers displayed n‐channel behaviors with an electron mobility in the order of 10^?4 cm² V^?1 s^?1. In contrast, the P2 ‐based devices exhibited only p‐channel charge transportation characteristics with a hole mobility in the order of 10^?3 cm² V^?1 s^?1. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2356–2366     

Perylene diimide copolymers with dithienothiophene and dithienopyrrole: Use in n‐channel and ambipolar field‐effect transistors

Solution‐processable polymers consisting of perylene diimide (PDI) acceptor moieties alternating with dithienothiophene (DTT), N‐dodecyl‐dithienopyrrole (DTP), or oligomers of these donor groups have been synthesized. We have, in addition to varying the donor, varied the N,N′ substituents of the PDIs. The thermal, optical, electrochemical, and charge‐transport properties of the polymers have been investigated. The polymers show broad absorption extending from 300 to 1000 nm with optical band gaps as low as 1.2 eV; the band gap decreases with increasing the conjugation length of donor block, or by replacement of DTT by DTP. The electron affinities of the polymers, estimated from electrochemical data, range from ?3.87 to ?4.01 eV and are slightly affected by the specific choice of donor moiety, while the estimated ionization potentials (?5.31 to ?5.92 eV) are more sensitive to the choice of donor. Bottom‐gate top‐contact organic field‐effect transistors based on the polymers generally exhibit n‐channel behavior with electron mobilities as high as 1.7 × 10^–2 cm²/V/s and on/off ratios as high as 10⁶; one PDI‐DTP polymer is an ambipolar transport material with electron mobility of 4 × 10^–4 cm²/V/s and hole mobility of 4 × 10^–5 cm²/V/s in air. There is considerable variation in the charge transport properties of the polymers with the chemical structures. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Low bandgap π‐conjugated copolymers based on fused thiophenes and benzothiadiazole: Synthesis and structure‐property relationship study

A series of low bandgap conjugated polymers consisting of benzothiadiazole alternating with dithienothiophene (DTT) or dithienopyrrole (DTP) unit with or without 3‐alkylthiophene bridge have been synthesized. Effect of the fused rings and 3‐alkylthiophene bridge on the thermal, optical, electrochemical, charge transport, and photovoltaic properties of these polymers have been investigated. These polymers show broad absorption extending from 300 to 1000 nm with optical bandgaps as low as 1.2 eV; the details of which can be varied either by incorporating 3‐alkylthiophene bridge or by replacing DTT with DTP. The LUMO levels (?2.9 to ?3.3 eV) are essentially unaffected by the specific choice of donor moiety, whereas the HOMO levels (?4.6 to ?5.6 eV) are more sensitive to the choice of donor. The DTT and DTP polymers with 3‐alkylthiophene bridge were found to exhibit hole mobilities of 8 × 10^?5 and 3 × 10^?2 cm² V^?1 s^?1, respectively, in top‐contact organic field‐effect transistors. Power conversion efficiencies in the range 0.17–0.43% were obtained under simulated AM 1.5, 100 mW cm^?2 irradiation for polymer solar cells using the DTT and DTP‐based polymers with 3‐alkylthiophene bridge as donor and fullerene derivatives as acceptor. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5498–5508, 2009