Effect of backbone structures on photovoltaic properties in naphthodithiophene‐based copolymers

A “zigzag” naphthodithiophene‐based copolymer, poly[4,9‐bis(2‐ethylhexyloxy)naphtho[1,2‐b:5,6‐b′]dithiophene‐2,7‐diyl‐alt‐1,3‐(5‐heptadecan‐9‐yl)‐4H‐thieno[3,4‐c]pyrrole‐4,6‐dione] (P1) is synthesized and its properties are compared to “linear” naphthodithiophene‐based copolymer, poly[4,9‐bis(2‐ethylhexyloxy)naphtho[2,3‐b:6,7‐d′]dithiophene‐2,7‐diyl‐alt‐1,3‐(5‐heptadecan‐9‐yl)‐4H‐thieno[3,4‐c]pyrrole‐4,6‐dione] (P2). The field‐effect carrier mobilities and the optical, electrochemical, and photovoltaic properties of the copolymers are systematically investigated. The results suggest that the backbone of the copolymer structure significantly influences the band gap, electronic energy levels, carrier mobilities, and photovoltaic properties of the resultant thin films. In this work, the zigzag naphtho[1,2‐b:5,6‐b′]dithiophene‐based copolymer displays a good hole mobility and a high open‐circuit voltage; however, polymer solar cells in which the linear naphtho[2,3‐b;6,7‐d′]dithiophene‐based copolymer is used as the electron donor material perform better than the cells prepared using the zigzag naphtho[1,2‐b:5,6‐b′]dithiophene‐based copolymer. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 305–312     

Synthesis and characterization of copolymers based on cyclopenta[c]thiophene and bithiazole and their transistor properties

Two new copolymers, P1 and P2 , containing 5,5‐bis(dodecyloxymethyl)?5,6‐dihydro‐4H‐cyclopenta[c]thiophene (DCPT) or DCPT‐based thiophene trimer (as donor) and 4,4′‐dibutyl‐2,2′‐bithiazole (BTz, as weak acceptor) have been synthesized. To reduce the steric hindrance and enhance the conjugation, the thiophene spacers have been incorporated between DCPT and BTz in P2 , which play an important role in maintaining the side chain ordering and π‐stacking interactions. Both the polymers showed π‐stacking with similar distances (～0.37 nm) but with larger extent in P2 . Combination of DCPT with BTz has resulted in low lying HOMO levels for the resulting polymers with significant improvement in oxidative stability. P1 and P2 showed p‐type mobility of 0.03 and 0.052 cm² V^?1 s^?1 with current on/off ratio (I_on/I_off) in the order of 10⁴ and 10³, respectively. These differences in characteristics may be attributed to the variation in donor (D)–acceptor (A) property, supramolecular ordering, extent of π‐stacking, and film microstructure. The polymers were further characterized by GPC, TGA, DSC, PXRD, cyclic voltammetry, and atomic force microscopy. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4481–4488     

Alternating copolymers of electron‐rich arylamine and electron‐deficient 2,1,3‐benzothiadiazole: Synthesis,characterization and photovoltaic properties

A series of alternating copolymers of electron‐rich arylamine and electron‐deficient 2,1,3‐benzothiadiazole (BT), PV‐BT, DP‐BT, and TP‐BT, were synthesized by Heck coupling reaction. UV–vis absorption and fluorescence spectra show that the copolymerization of electron‐rich diphenylamine (DP), triphenylamine (TP), MEH‐PV (PV), and electron‐deficient BT results in low‐bandgap conjugated polymers. Within the three copolymers of PV‐BT, DP‐BT, and TP‐BT, TP‐BT possesses the highest hole mobility of 4.68 × 10^{? 5} cm²/V, as determined from the space charge limited current (SCLC) model. The bulk heterojunction‐typed polymer solar cells (PSCs) were fabricated with the blend of the copolymers and PCBM as the photosensitive layer. The power conversion efficiencies (PCE) of the PSCs based on PV‐BT, DP‐BT, and TP‐BT reached 0.26%, 0.39%, and 0.52%, respectively, under the illumination of AM 1.5, 100 mW/cm². The results indicate that TP‐BT is a promising photovoltaic polymer for PSCs. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3861–3871, 2007     

Synthesis and photovoltaic properties of two‐dimensional copolymers based on novel benzothiadiazole and quinoxaline acceptors with conjugated dithienylbenzothiadiazole pendants

Two novel acceptors of benzo[c][1,2,5]thiadiazole and quinoxaline with conjugated dithienylbenzothiadiazole pendants were first designed and synthesized for building efficient photovoltaic copolymers. Based on benzo[1,2‐b;3,4‐b′]dithiophene donors and the two acceptors, two new copolymers have been prepared by Stille coupling polymerization. The resulting copolymers were characterized by ¹H NMR, gel permeation chromatography, and thermogravimetric analysis. UV–Visible absorption and cyclic voltammetry measurements indicated that the two copolymers possessed strong and broad absorption in the range of 300–700 nm, and deep‐lying energy levels of highest occupied molecular orbitals. The polymer photovoltaic devices based on benzo[c][1,2,5]thiadiazole‐based copolymer/phenyl‐C₇₁‐butyric acid methyl ester exhibited a power conversion efficiency of 2.42%, attributed to its relatively better light‐harvesting ability and active film morphology. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 668–677     

Synthesis,characterization, and photovoltaic properties of novel conjugated copolymers derived from phenothiazines

Two novel series of soluble alternating conjugated copolymers comprising 10‐alkylphenothiazine and bithiophene or 3‐pentylthieno[3,2‐b]thiophene moieties were synthesized using palladium‐catalyzed Suzuki coupling reaction. The structures of the polymers and their thermal, photophysical, electrochemical, and photovoltaic properties were characterized and investigated. The polymers exhibited good thermal stability with decomposition temperature in the region of 342–390 °C and their glass transition temperatures (T_g) ranging from 126 to 150 °C. All polymers demonstrate broad optical absorption in the region of 300–500 nm with efficient blue‐green light emission. They showed ambipolar redox properties with low HOMO levels around ?5.13 eV. Polymer solar cells were fabricated using blends of the copolymers and [6,6]‐phenyl‐C61‐butyric acid methyl ester (PCBM) in a 1:1 weight ratio. The maximum power conversion efficiency (η = 0.24%) was measured for the poly[3,7‐ (10‐hexylphenothiazine)‐alt‐bithiophene] as donor under simulated sun light (1000 W/m²). Open circuit voltages of up to 0.8 V have been obtained. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5266–5276, 2007     

Synthesis and photovoltaic properties of conjugated copolymers based on benzimidazole and various thiophene

A new accepter unit, dimethyl‐2H‐benzimidazole, was prepared and used for the synthesis of the conjugated polymers containing electron donor–acceptor pair for organic photovoltaics (OPVs). Dimethyl‐2H‐benzimidazole unit was designed to substitute the BT unit of poly(N‐9′‐heptadecanyl‐2,7‐carbazole‐alt‐5,5‐(4′,7′‐di‐2‐thienyl‐2′,1′,3′‐benzothiadiazole)) (PCDTBT). A series of new semiconducting polymers with 2,2‐dimethyl‐2H‐benzimidazole, 9‐heptadecanyl‐9H‐carbazole, and thiophene (or bithiophene) units was synthesized using Stille polymerization to generate PCDTMBIs (or PCBBTMBIs). In dimethyl‐2H‐benzimidazole, the sulfur at 2‐position of BT unit was replaced with dialkyl substituted carbon, while keeping the 1,2‐quinoid form, to improve the solubility of the polymers. The absorption spectra of PCDTMBIs with thiophene units exhibit two maximum peaks at about 430 and 613–645 nm in solution. The solutions of PCBBTMBIs show two absorption peaks at about 445–456 and 630–645 nm which is red‐shifted about 20 nm when compared with PCDTMBIs caused by the introduction of bithiophene units. In most efficient polymer PCBBTMBI3, the device annealed at 100 °C for 10 min demonstrated a V_OC value of 0.60 V, a J_SC value of 4.31 mA/cm², and a FF of 0.35, leading to the power conversion efficiency (PCE) of 0.91%, under white light illumination (AM 1.5 G and 100 mW/cm²). © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis and properties of fluorene‐based polyheteroarylenes for photovoltaic devices

Novel copolymers consisting of the alternating push–pull comonomers fluorene and thieno[3,4‐b]pyrazine/quinoxaline were synthesized by a palladium‐catalyzed Suzuki cross‐coupling reaction in 60–80% yields. The structure of the deeply colored copolymers was confirmed with ¹H and ¹³C NMR. All the new materials were characterized with spectroscopic and electrochemical methods. Bulk heterojunction organic solar cells based on some of the novel polymers in combination with the well‐known fullerene acceptor [6,6]‐phenyl C₆₁–butyric acid methyl ester were fabricated, and their photovoltaic parameters were measured. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6952–6961, 2006     

Synthesis,characterization, and photovoltaic properties of dithienylbenzobisazole‐dithienylsilole copolymers

Three conjugated polymers comprised of dioctyl‐dithieno‐[2,3‐b:2',3'‐d]silole and a donor‐acceptor‐donor triad of either cis‐benzbisoxazole, trans‐benzobisoxazole or trans‐benzobisthiazole were synthesized via the Stille cross‐coupling reaction. The impact of varying the heteroatoms and/or the location within the benzobisazole moiety on the optical and electronic properties of the resulting polymers was evaluated via cyclic voltammetry and UV‐Visible spectroscopy. All of the polymers have similar optical band‐gaps of ～1.9 eV and highest occupied molecular orbital levels of ? 5.2 eV. However, the lowest unoccupied molecular orbitals (LUMO) ranged from ? 3.0 to ? 3.2 eV. Interestingly, when the polymers were used as donor materials in bulk‐heterojunction photovoltaic cells with PC₇₁BM as the electron‐acceptor, the benzobisoxazole‐based polymers gave slightly better results than the benzobisthiazole‐containing polymers with power conversion efficiencies up to 3.5%. These results indicate that benzobisoxazoles are promising materials for use in OPVs. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1533–1540     

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     

Low band gap copolymers based on thiophene and quinoxaline: Their electronic energy levels and photovoltaic application

Low band gap conjugated copolymers containing donor (thiophene)‐acceptor (quinoxaline, Qx ) were synthesized via Stille coupling polymerization. The resulting copolymers were characterized by ¹H NMR, element analysis, GPC, TGA, and DSC. UV‐vis spectra indicated that the increase in the content of quinoxaline units increased the interaction strengthen of the polymer main chains and caused a red‐shift in the optical absorbance. Cyclic voltammetry was used to estimate energy levels of the lowest unoccupied molecular orbit (LUMO) and the highest occupied molecular orbit (HOMO), and the band gap (E_g) of the copolymers. The basic electronic structures of the copolymers were also studied by density‐functional theory (DFT) calculations. Both the experimental and calculation results indicated an increase in the HOMO energy level with increasing the content of quinoxaline units, whereas the corresponding change in the LUMO energy level is much smaller. Polymer photovoltaic cells (PVCs) were fabricated with the structure of ITO/PEDOT:PSS (30 nm)/active layer (80 nm)/Ca (8 nm)/Al(140 nm). The results show that the introduction of a proper amount of electron‐acceptor groups in the polymer main chains induces an extension of the absorption spectra and improves the photovoltaic properties of the copolymers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3399–3408, 2009     

Synthesis,two‐photon absorption,and optical power limiting of new linear and hyperbranched conjugated polyynes based on bithiazole and triphenylamine

Two new linear and hyperbranched conjugated polymers P1 and P2 have been synthesized by Sonogashira coupling reaction, in which the main chain consists of bithiazole moieties as electron acceptors and triphenylamino groups as donors. The conjugated polymers were characterized by TGA, UV–vis absorption, fluorescence emission, electrochemical cyclic voltammetry, and two‐photon absorption measurements. They exhibited excellent solubility in organic solvents and high thermal stability (5% of weight loss at 299 °C). The two‐photon absorption cross sections (σ) measured by the open aperture Z‐scan technique using 140 femtosecond (fs) pulse were determined to be 1014 and 552 GM per repeating unit for P1 and P2 , respectively. This result shows that the σ of linear conjugated P1 is higher than that of hyperbranched P2 , indicating that the linear polymer offers better intramolecular charge transfer ability. In THF, P1 and P2 exhibit intense frequency up‐converted fluorescence under the excitation of 140 fs pulses at 800 nm with the peaks located at 580 and 548 nm, respectively. Meanwhile, the optical limiting behaviors for the polymers were studied by using a focused 800 nm laser beam of 140 fs duration. It was found that these polymers also exhibit good optical‐limiting properties and make them potential candidates for optical limiters in the photonic fields. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis and photovoltaic properties of copolymers with a fluoro quinoxaline unit

Two novel accepter units, namely, difluoroquinoxaline and monofluoroquinoxaline, were prepared and used for the synthesis of the conjugated polymers containing electron donor–acceptor pairs for use in organic photovoltaics. The introduction of a fluorine atom into the quinoxaline moiety resulted in polymers with lowered highest occupied molecular orbital (HOMO) energy levels; this increased the open circuit voltage of the devices based on the synthesized polymers. The conjugated polymers containing difluoroquinoxaline and monofluoroquinoxaline, namely, thiophene and benzodithiophene, were synthesized using the Stille polymerization reaction to produce PEHBQxF2, PEHBQxF1, PEHBDTQxF2, and PEHBDTQxF1. The HOMO energy levels of PEHBQxF2, PEHBQxF1, PEHBDTQxF2, and PEHBDTQxF1 were determined to be −5.66, −5.52, −5.54, and −5.39 eV, respectively. The device with PEHBDTQxF2/PC₇₁BM (1:2, w/w) and containing diiodooctane (3 vol %) exhibited the best photovoltaic performance, with its V_OC being 0.79 V, J_SC being 10.44 mA/cm², FF being 68%, and PCE being 5.58%. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 821–830     

Low‐bandgap quinoxaline‐based D–A‐type copolymers: Synthesis,characterization, and photovoltaic properties

Three classes of quinoxaline (Qx)‐based donor–acceptor (D–A)‐type copolymers, poly[thiophene‐2,5‐diyl‐alt‐2,3‐bis(4‐(octyloxy)phenyl‐quinoxaline‐5,8‐diyl] P(T‐Qx), poly{4,8‐bis(2‐ethylhexyloxy)benzo[1,2‐b:4,5‐b′]dithiophene‐2,6‐diyl‐alt‐2,3‐bis(4‐(octyloxy)phenyl‐quinoxaline‐5,8‐diy} P(BDT‐Qx), and poly{4,8‐bis(2‐ethylhexyloxy)benzo[1,2‐b:4,5‐b′]dithiophene‐2,6‐diyl‐alt‐(5′,8′‐di‐2‐thienyl‐2,3‐bis(4‐octyloxyl)phenyl)‐quinoxaline‐5,5‐diyl} P(BDT‐DTQx), were synthesized via a Stille coupling reaction. The Qx unit was functionalized at the 2‐ and 3‐positions with 4‐(octyloxy)phenyl to provide good solubility and to reduce the steric hindrance. The absorption spectra of the Qx‐containing copolymers could be tuned by incorporating three different electron‐donating moieties. Among these, P(T‐Qx) acted as an electron donor and yielded a high‐performance solar cell by assuming a rigid planar structure, confirmed by differential scanning calorimetry, UV–vis spectrophotometer, and density functional theory study. In contrast, the P(BDT‐Qx)‐based solar cell displayed a lower power conversion efficiency (PCE) with a large torsional angle (34.7°) between the BDT and Qx units. The BDT unit in the P(BDT‐DTQx) backbone acted as a linker and interfered with the formation of charge complexes or quinoidal electronic conformations in a polymer chain. The PCEs of the polymer solar cells based on these copolymers, in combination with [6,6]‐phenyl C70 butyric acid methyl ester (PC₇₁BM), were 3.3% [P(T‐Qx)], 1.9% [P(BDT‐Qx)], and 2.3% [P(BDT‐DTQx)], respectively, under AM 1.5G illumination (100 mW cm^?2). © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

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     

Poly(alkylthio‐p‐phenylenevinylene): Synthesis and electroluminescent and photovoltaic properties

Two alkylthio‐substituted poly(p‐phenylenevinylene) (AT–PPV) derivatives, poly(2‐octylthio‐p‐phenylenevinylene) (OT–PPV) and poly[5‐methoxy‐2‐(2′‐ethyl‐hexylthio)‐p‐phenylenevinylene] (MEHT–PPV), were synthesized by a Heck coupling reaction for the investigation of the effect of alkylthio groups on the optoelectronic properties of poly(p‐phenylenevinylene) derivatives. The absorption peaks of OT–PPV and MEHT–PPV solutions were located at 431 and 438 nm, respectively. As for solid films, an OT–PPV film showed an absorption maximum wavelength at 444 nm, 13 nm redshifted in comparison with its solution value, whereas an MEHT–PPV film displayed the same absorption peak position as its dilute solution; this indicated that there was no interchain interaction in the MEHT–PPV film. Polymeric light‐emitting diodes (PLEDs) and polymer solar cells (PSCs) based on OT–PPV and MEHT–PPV were fabricated and characterized. Very narrow bandwidths of the electroluminescence (EL) spectra of the two AT–PPVs were found, with the full width at half‐maximum of the emission being 40 and 47 nm for OT–PPV and MEHT–PPV, respectively. The maximum EL efficiency of the single‐layer PLED based on MEHT–PPV with Al as a cathode reached 1.49 cd/A. The PSC based on a blend of OT–PPV and [6,6]‐phenyl‐C₆₁ butyric acid methyl ester (PCBM) showed the power conversion efficiency of 1.4% under the illumination of AM1.5 (80 mW/cm²). © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1279–1290, 2006     

Synthesis and photovoltaic behavior of two new alternative donor–acceptor conjugated copolymers containing isoindigo moiety

Two donor–acceptor copolymers (P1 and P2) containing isoindigo as the acceptor unit and the benzodithiophene and bisthiophene‐dithieno[3,2‐b:2′,3′‐d]‐pyrrole as the donor unit have been designed and synthesized by the Pd‐catalyzed Stille coupling reaction. The copolymers show broad and flat absorption, exhibit good solubility, and thermal stability, but possess optical bandgaps of 1.62 and 1.42 eV, respectively, and different donor–acceptor distance, of which the former is shorter than the later. The power conversion efficiency of the polymer solar cells based on P2:PC₆₁BM (1:1 wt%) reached 1.86% with open‐circuit voltage of 0.54 V and a short‐circuit current of 6.36 mA/cm², under the illumination of AM 1.5, 100 mW/cm². Copyright © 2013 John Wiley & Sons, Ltd.     

Pyrene–benzothiadiazole‐based copolymers for application in photovoltaic devices

The preparation and characterization of four narrow band gap pyrene–benzothiadiazole‐based alternating copolymers are presented. An investigation of the impact of attaching different solubilizing groups to the pyrene repeat units on the optical, electrochemical, and thermal properties of the resulting materials was undertaken along with studies on the aggregation of polymer chains in the solid state. Unsurprisingly, polymers which had the smaller 2‐ethylhexyl chains attached to the pyrene units (PP_EH‐DTBT and PP_EH‐DTffBT) displayed lower molecular weights relative to polymers with larger 2‐hexyldecyl substituents (PP_HD‐DTBT and PP_HD‐DTffBT). Despite this, the 2‐ethylhexyl substituted polymers displayed narrower optical band gaps relative to their analogous 2‐hexyldecyl substituted polymers. Of all polymers synthesized, PP_EH‐DTBT displayed the lowest optical band gap (1.76 eV) in the series. All polymers display degradation temperatures in excess of 300°C. Polymers with smaller alkyl chains on the pyrene units display shallower highest occupied molecular orbital levels, which could be due to increased intramolecular charge transfer between the donor and acceptor units. Preliminary investigations on bulk heterojunction solar cells with a device structure indium tin oxide/poly(3,4‐ethylenedioxythiophene) : polystyrene sulfonate /Polymer : PC₇₀BM/Ca/Al were undertaken. Polymer/PC₇₀BM blend ratios of one third were used in these studies and have indicated that PP_EH‐DTBT displayed the highest efficiency with a power conversion efficiency of 1.86%. Copyright © 2016 John Wiley & Sons, Ltd.     

Synthesis and applications of cyano‐vinylene‐based polymers containing cyclopentadithiophene and dithienosilole units for photovoltaic cells

Two β‐cyano‐thiophenevinylene‐based polymers containing cyclopentadithiophene ( CPDT‐CN ) and dithienosilole ( DTS‐CN ) units were synthesized via Stille coupling reaction with Pd(PPh₃)₄ as a catalyst. The effects of the bridged atoms (C and Si) and cyano‐vinylene groups on their thermal, optical, electrochemical, charge transporting, and photovoltaic properties were investigated. Both polymers possessed the highest occupied molecular orbital (HOMO) levels of about ?5.30 eV and the lowest unoccupied molecular orbital (LUMO) levels of about ?3.60 eV, and covered broad absorption ranges with narrow optical band gaps (ca. 1.6 eV). The bulk heterojunction polymer solar cell (PSC) devices containing an active layer of electron‐donor polymers ( CPDT‐CN and DTS‐CN ) blended with an electron‐acceptor, that is, [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PC₆₁BM) or [6,6]‐phenyl‐C₇₁‐butyric acid methyl ester (PC₇₁BM), in different weight ratios were explored under 100 mW/cm² of AM 1.5 white‐light illumination. The PSC device based on DTS‐CN: PC₇₁BM (1:2 w/w) exhibited a best power conversion efficiency (PCE) value of 2.25% with V_oc = 0.74 V, J_sc = 8.39 mA/cm², and FF = 0.36. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.     

Diazaisoindigo bithiophene and terthiophene copolymers for application in field‐effect transistors and solar cells

Two donor–acceptor conjugated polymers with azaisoindigo as acceptor units and bithiophene and terthiophene as donor units have been synthesized by Stille polymerization. These two polymers have been successfully applied in field‐effect transistors and polymer solar cells. By changing the donor component of the conjugated polymer backbone from bithiophene to terthiophene, the density of thiophene in the backbone is increased, manifesting as a decrease in both ionization potential and in electron affinity. Therefore, the charge transport in field‐effect transistors switches from ambipolar to predominantly hole transport behavior. PAIIDTT exhibits hole mobility up to 0.40 cm²/Vs and electron mobility of 0.02 cm²/Vs, whereas PAIIDTTT exhibits hole mobility of 0.62 cm²/Vs. Polymer solar cells were fabricated based on these two polymers as donors with PC₆₁BM and PC₇₁BM as acceptor where PAIIDTT shows a modest efficiency of 2.57% with a very low energy loss of 0.55 eV, while PAIIDTTT shows a higher efficiency of 6.16% with a higher energy loss of 0.74 eV. Our results suggest that azaisoindgo is a useful building block for the development of efficient polymer solar cells with further improvement possibility by tuning the alternative units on the polymer backbone. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2691–2699