Random benzotrithiophene-based donor-acceptor copolymers for efficient organic photovoltaic devices

A series of benzotrithiophene-containing random terpolymers for polymer solar cells is reported. Through variations of the two other components in the terpolymers, the absorption profile and the frontier energy levels are optimized and maximum power conversion efficiencies are nearly doubled (5.14%) relative to the parent alternating copolymer.     

Synthesis and photovoltaic properties of copolymers based on bithiophene and bithiazole

Three simple structured D‐A copolymers, PBTBTz‐1 , PBTBTz‐2 , and PBTBTz‐3 , containing bithiophene (BT) donor unit and bithiazole (BTz) acceptor unit with different alkyl chain length were synthesized by the Pd‐catalyzed Stille‐coupling method. The copolymers were characterized by thermogravimetric analysis, UV–vis absorption, electrochemical cyclic voltammetry, and photovoltaic measurements. The results indicate that the introduction of BTz unit to the polythiophene main chain effectively decreases highest occupied molecular orbital levels of the copolymers and increases the open circuit voltage (V_oc) of polymer solar cells (PSCs) based on the copolymers as donor, and the alkyl chain length influences the photovoltaic properties of the polymers significantly. The PSCs based on PBTBTz‐2 and PBTBTz‐3 show higher V_oc up to 0.77 and 0.81 V, respectively. The power conversion efficiency of the PSC based on PBTBTz‐2 :PC₇₀BM = 1:1(w/w) reached 2.58% with short circuit current of 8.70 mA/cm², under the illumination of AM1.5, 100 mW/cm². © 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     

Synthesis, characterization and photovoltaic properties of thiophene copolymers containing conjugated side-chain

Five side-chain conjugated polythiophene derivatives, P1-P5, were synthesized by Stille coupling reaction. The effects of side-chain structures, bearing CC double bond, CC triple bond as well as different number of methoxy substituents on the benzene ring of the side-chains, on the optical, electrochemical, and photovoltaic properties of the polymers were investigated. From P1 to P3, the effect of CC triple bond and CC double bond was compared. The results indicate that the content of the thiophene units with the CC triple bond in their conjugated side-chains not only influences the absorption shape and intensity, but also influences the energy bandgap and the photovoltaic properties of the polymers. From P3 to P5, the effect of methoxy substituents on the benzene ring of the conjugated side-chains was compared. On increasing the number of the methoxy groups on the benzene ring of the conjugated side chains, the visible π-π^∗ absorption of the conjugated polymer backbone become stronger both in solution and in film. Electron-donating ability of the methoxy groups decreased the bandgap of the polymers. The best polymer solar cell based on P5 with a structure of ITO/PEDOT:PSS/Polymer:PCBM (1:1 wt/wt)/Mg/Al showed a power conversion efficiency of 1.45% under the illumination of AM1.5, 80 mW/cm².     

New narrow-band-gap conjugated copolymers based on benzodithiophene: Synthesis and photovoltaic properties

Four new alternating narrow-band-gap copolymers based on benzodithiophene are synthesized under conditions of the Stille reaction. In comparison to benzodithiophene homopolymers, all these copolymers show good solubility in common organic solvents and broad absorption in the visible spectrum of sunlight. The band gaps of the polymer films, as estimated from the cyclic voltammetry data, vary within 1.34–2.28 eV, and the position of the highest occupied molecular orbital lies in the range 4.99–5.72 eV. The values of the open-circuit voltage and the efficiency of polymer solar cells based on the copolymers are within 0.22–0.65 V and 0.02–0.48%, respectively.     

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,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 low-bandgap copolymers based on new benzothiadiazole derivatives with different conjugated arylvinylene side chains

A new series of 2,1,3-benzothiadiazole (BT) acceptors with different conjugated aryl-vinylene side chains have been designed and used to build efficient low-bandgap (LBG) photovoltaic copolymers. Based on benzo[1,2-b:3,4-b']dithiophene and the resulting new BT derivatives, three two-dimensional (2D)-like donor (D)-acceptor (A) conjugated copolymers have been synthesised by Stille coupling polymerisation. These copolymers were characterised by NMR spectroscopy, gel-permeation chromatography, thermogravimetric analysis and differential scanning calorimetry. UV/Vis absorption and cyclic voltammetry measurements indicated that their optical and electrochemical properties can be facilely modified by changing the structures of the conjugated aryl-vinylene side chains. The copolymer with phenyl-vinylene side chains exhibited the best light harvesting and smallest bandgap of the three copolymers. The basic electronic structures of D-A model compounds of these copolymers were also studied by DFT calculations at the B3LYP/6-31G* level of theory. Polymer solar cells (PSCs) with a typical structure of indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophene) (PEDOT):poly(styrenesulfonate) (PSS)/copolymer:[6,6]-phenyl-C(61) (C(71) )-butyric acid-methyl ester (PCBM)/calcium (Ca)/aluminum (Al) were fabricated and measured under the illumination of AM1.5G at 100?mW?cm(-2) . The results showed that the device based on the copolymer with phenyl-vinylene side chains had the highest efficiency of 2.17?% with PC(71) BM as acceptor. The results presented herein indicate that all the prepared copolymers are promising candidates for roll-to-roll manufacturing of efficient PSCs. Suitable electronic, optical and photovoltaic properties of BT-based copolymers can also be achieved by fine-tuning the structures of the aryl-vinylene side chains for photovoltaic application.     

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 of new siloxane urethane block copolymers and their properties

Siloxane urethane block copolymers were prepared with siloxanes as the soft segment. Films were cast from a variety of solvents. Solvent has an effect on the segregation of soft and hard segments. Surface studies, including ESCA, EDS, and FT-IR, show well segregated block copolymers with enhanced siloxane on the surface. DSC studies show a low mp (-44°C) for the soft segment and a T_g for the hard segment above room temperature. These materials show higher thermal stability compared to polyether urethane block copolymers. These copolymers also show relatively good resistance to exposure to oxygen plasma and show improved flame retardancy compared to nonsiliconated, polyether polyurethane block copolymers. © 1994 John Wiley & Sons, Inc.     

Synthesis and electronic properties of donor-acceptor pi-conjugated siloles

An efficient method is presented for the synthesis of novel donor-acceptor silole chromophores through selective monohalogenation of 2,5-dimetallosiloles followed by Negishi alkyne cross-coupling reactions. The electronic properties and crystal packing of these new siloles can be controlled through judicious combinations of peripheral functional groups.     

Synthesis and photovoltaic properties of fluorene-based copolymers with narrow band-gap units on the side chain

A series of novel polyfluorene copolymers are developed by covalently attaching narrow band gap aryl-heterocycle units of Th-BT-TPA to the side chain of polyfluorene with an alkyl phenyl spacer through Pd-catalyzed Suzuki coupling reactions. The resulting copolymers are soluble in common organic solvents. The electrochemical, optical, and photovoltaic properties of the copolymers are studied. Electrochemical and optical analysis reveal that these polymers exhibit relatively low band gaps from 1.95 to 2.00 eV and exhibit strong absorption in the 300-620 nm region. BHJ solar cells blending copolymers PF-MR15-DBT35 with [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) (1:1 weight ratio) as the active layer present a high open-circuit voltage (V_oc∼1.0 V) and a power conversion efficiency of 0.7% under simulated solar light AM1.5G (80 mW/cm²). Further investigations of other polyfluorene copolymers with narrow band gap aryl-heterocycle units on the side chain are in progress.     

Design and synthesis of new donor-acceptor type conjugated copolymers derived from thiophenes

A new series of donor-acceptor type poly(thiophene) derivatives (P1-P3) were synthesized starting from thiodiglycolic acid and diethyl oxalate through multistep reactions. In the final step, the polymerization was carried out using Wittig reaction. This is a good synthetic route for the preparation of any desired p- and n-type copolymers. The optical and potential charge-transporting properties of the copolymers were investigated by UV-vis, fluorescence emission spectroscopy and cyclic voltammetry. The copolymers exhibited bluish-green/green fluorescence in their thin film forms. Cyclic voltammetry experiments showed that these copolymers have low-lying LUMO energy levels ranging from −2.98 to −3.11 eV and high lying HOMO energy levels ranging from −5.45 to −5.65 eV. The optical and electrochemical studies reveal that new copolymers are new promising materials for the development of efficient polymer light emitting diodes.     

一种三元共聚物磷酸盐的合成及性能研究

由丙烯酰胺、丙烯酸、3-二甲胺基烯丙基磷酸在过硫酸铵-亚硫酸氢钠氧化还原引发体系下合成了一种新型的AM/AA/DMAAPA三元共聚物.确立了最佳反应条件:AM/AA= 3/1(wt％),引发剂用量0.5wt％,pH为7,反应温度为40℃;并通过红外光谱分析确认了AM/AA/DMAAPA三元共聚物结构.当Na+;Cab,...     

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.     

Synthesis and photovoltaic properties of new thieno[3,2-b]indole-based dyes

Russian Chemical Bulletin - New dyes of the 3-[5-(4-alkyl-4H-thieno[3,2-b]indol-2-yl)thiophen-2-yl]-2-cyanoacrylic acid series were prepared based on 2-(thien-2-yl)-substituted thieno[3,2-b]indole...     

Synthesis and properties of new block copolymers based on polydimethylsiloxane and tetraphenylethylene-containing polyimide

New polydimethylsiloxane (PDMS)-polyimide block copolymers were synthesized by the solution polycondensation of aminopropyl-terminated polydimethylsiloxane, 1,1-bis(4-aminophenyl)-2,2-diphenylethylene, and 3,3′,4,4′-benzophenonetetracarboxylic dithioanhydride in pyridine. New 1,3-bis(3-aminopropyl)tetramethyldisiloxane (BADS)-based random copolyimides were also prepared. The inherent viscosities of all the random and block copolyimides were in the range of 0.13–0.90 dL/g in N-methyl-2-pyrrolidone. These copolymers were soluble in N,N-dimethylacetamide, N-methyl-2-pyrrolidone, and m-cresol. All the BADS-based random copolymers and PDMS-containing copolymers with PDMS content above 42 wt % were soluble in tetrahydrofuran and chloroform. Transparent or somewhat cpaque films were prepared by casting from the reaction solutions. The BADS-based random copolyimides had one glass transition temperature (T_g) in the whole composition ranges, which showed single phase nature of the copolymers. On the other hand, the PDMS-polyimide block copolymers had double T_gS, indicating phase-separated morphology. The block copolymers containing PDMS content above 73 wt % behaved like a high temperature elastomer. © 1993 John Wiley & Sons, Inc.     

Synthesis and properties of fullerene-containing N-vinylpyrrolidone copolymers

Branched copolymers containing covalently bonded fullerene C₆₀ were synthesized by cross-linking radical copolymerization of N-vinylpyrrolidone with triethylene glycol dimethacrylate in toluene saturated with fullerene. Their composition was studied by elemental analysis and IR and electronic absorption spectroscopy. The concentration of double bonds, characteristic viscosity, and glass-transition temperature of the fullerene-containing copolymers were determined by ozonoliysis, viscosimetry, and differential scanning calorimetry. The parameters and thermal stability of the fullerene-containing copolymers were compared with those of their non-functionalized analogs.     

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