Band gap tuning of narrow‐polydispersity two‐dimensional conductive polymers with electroactive side‐chains

A series of two‐dimensional donor–acceptor–donor (D1–A(D2)) type of conducting polymers (CPs) all with electroactive bulky side chain structure has been designed, synthesized, and investigated by introducing the donor–acceptor (D1–A) thiophene–quinoxaline moiety in the main chain alongside and additional donor and hole transporting units in the side chain. All the UV‐vis spectra of the 2D polymers, PTPQT, PFPQT, and PCPQT, each with triphenylamine, fluorene, and carbazole units as the D2 side chain, possess strong intramolecular charge transfer absorption, thus resulting in better light harvesting. Their optical and electronic properties were thoroughly explored experimentally and computationally. The effect of molecular weight of the narrow polydispersity polymers on their optoelectronic property was studied in detail. In summary, the 2‐D CPs show potential for use as an active material in optoelectronic devices. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1217–1227     

Synthesis and characterization of thieno[3,2‐b]thiophene‐isoindigo‐based copolymers as electron donor and hole transport materials for bulk‐heterojunction polymer solar cells

A novel class of thieno[3,2‐b]thiophene (TT) and isoindigo based copolymers were synthesized and evaluated as electron donor and hole transport materials in bulk‐heterojunction polymer solar cells (BHJ PSCs). These π‐conjugated donor‐acceptor polymers were derived from fused TT and isoindigo structures bridged by thiophene units. The band‐gaps and the highest occupied molecular orbital (HOMO) levels of the polymers were tuned using different conjugating lengths of thiophene units on the main chains, providing band‐gaps from 1.55 to 1.91 eV and HOMO levels from ?5.34 to ?5.71 eV, respectively. The corresponding lowest unoccupied molecular orbital (LUMO) levels were appropriately adjusted with the isoindigo units. Conventional BHJ PSCs (ITO/PEDOT:PSS/active layer/interlayer/Al) with an active layer composed of the polymer and PC₇₁BM were fabricated for evaluation. Power conversion efficiency from a low of 1.25% to a high of 4.69% were achieved with the best performing device provided by the D?π?A polymer with a relatively board absorption spectrum, high absorption coefficient, and more uniform blend morphology. These results demonstrate the potential of this class of thieno[3,2‐b]thiophene‐isoindigo‐based polymers as efficient electron donor and hole transport polymers for BHJ PSCs. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Donor–acceptor‐integrated conjugated polymers based on carbazole[3,4‐c:5,6‐c]bis[1,2,5]thiadiazole with tight π–π stacking for photovoltaics

An original strategy to construct a new donor–acceptor (D–A)‐integrated structure by directly imposing “pull” unit on the “push” moiety to form fused ring architecture has been developed, and poly{N‐alkyl‐carbazole[3,4‐c:5,6‐c]bis[1,2,5]thiadiazole‐alt‐thiophene} (PCBTT) with D–A‐integrated structure, in which two 1,2,5‐thiadiazole rings are fixed on carbazole in 3‐, 4‐ and 5‐, 6‐position symmetrically and thiophene is used as bridge, has been synthesized. The interaction between pull and push units has fine tuned the HOMO/LUMO energy levels, and the resulting copolymer covers the solar flux from 300 to 750 nm. The interaction between pull and push units is worth noting that due to the fused five rings inducing strong intermolecular interaction, an extremely short π–π stacking distance of 0.32 nm has been achieved for PCBTT both in powder and solid states. This is the shortest π–π stacking distance reported for conjugated polymers. Additionally, an obvious intramolecular charge transfer and energy transfer from donor units to acceptor units have been detected in this D–A integration. A moderate‐to‐high open‐circuit voltage of ～0.7 V in PCBTT:[6,6]‐phenyl‐C61 butyric acid methyl ester (PCBM) (w/w = 1/2) solar cells is achieved due to the low‐lying HOMO energy level of PCBTT. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

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     

Novel low‐bandgap oligothiophene‐based donor‐acceptor alternating conjugated copolymers: Synthesis,properties, and photovoltaic applications

A series of novel soluble donor‐acceptor low‐bandgap‐conjugated polymers consisting of different oligothiophene (OTh) coupled to electron‐accepting moiety 2‐pyran‐4‐ylidenemalononitrile (PM)‐based unit were synthesized by Stille or Suzuki coupling polymerization. The combination of electron‐accepting PM building block with varied OTh_n (the number of thiophene unit increases from 3 to 5) results in enhanced π–π stacking in solid state and intramolecular charge transfer (ICT) transition, which lead to an extension of the absorption spectra of the copolymers. Cyclic voltammetry measurements and molecular orbital distribution calculations indicate that the highest occupied molecular orbitals (HOMO) energy levels could be fine‐tuned by changing the number of thiophene units of the copolymers, and the resulting copolymers possessed relatively low HOMO energy levels promising good air stability and high‐open circuit voltage (V_oc) for photovoltaic application. Bulk heterojunction photovoltaic devices were fabricated by using the copolymers as donors and (6,6)‐phenyl C₆₁‐butyric acid methyl ester as acceptor. It was found that the highest V_oc reached 0.94 V, and the short circuit currents (J_sc) were improved from 1.78 to 2.54 mA/cm², though the power conversion efficiencies of the devices were measured between 0.61 and 0.99% under simulated AM 1.5 solar irradiation of 100 mW/cm², which indicated that this series copolymers can be promising candidates for the photovoltaic applications. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2765–2776, 2010     

Introducing a new triazoloquinoxaline‐based fluorene copolymer for organic photovoltaics: Synthesis,characterization, and photovoltaic properties

A new donor‐acceptor copolymer consisting of triazoloquinoxaline and 9,9‐dialkylfluorene units on the main chain has been synthesized, characterized and evaluated as donor material in bulk heterojunction solar cells using PC₆₁BM as an acceptor. The resulting polymer PTQF showed good thermal stability and solubility in common organic solvents. Cyclic Voltammetry measurements showed that the PTQF has HOMO–LUMO energy levels of ?5.13 and ?3.62 eV, respectively. DFT calculations revealed that the HOMO is delocalized all over the thiophene and fluorene units and the LUMO is localized mainly on the triazole and pyrazine units. PTQF absorbs broadly in the visible region and exhibits a bandgap of 1.4 eV. Photovoltaic devices exhibited 1.7% efficiency for 1:2 PTQF:PC₆₁BM blend ratio using Ca/Ag electrodes. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Novel two‐dimensional donor–acceptor conjugated polymers containing quinoxaline units: Synthesis,characterization, and photovoltaic properties

Novel two‐dimensional donor–acceptor (D–A) structured conjugated polymers, P1–P4, were designed and synthesized by introducing electron‐deficient quinoxaline as core and electron‐rich alkoxyl‐phenylenevinylene in side chains and p‐phenylenevinylene, triphenylamine, or thiophene in main chain. Benefited from the D–A structures, the polymers possess low bandgaps of 1.75 eV, 1.86 eV, 1.59 eV, and 1.58 eV for P1, P2, P3, and P4, respectively, and show broad absorption band in the visible region: the shorter wavelength absorption peak at ～400 nm ascribed to the conjugated side chains and the longer wavelength absorption peak between 500 nm and 750 nm belonging to the absorption of the conjugated main chains. Especially, the absorption band of P4 film covers the whole visible range from 300 nm to 784 nm. The power conversion efficiencies of the polymer solar cells based on P1–P4 as donor and PCBM as acceptor are 0.029%, 0.14%, 0.46%, and 0.57%, respectively, under the illumination of AM 1.5, 100 mW/cm². The polymers with the low bandgap and broad absorption band are promising photovoltaic materials. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4038–4049, 2008     

A vinylene‐linked benzo[1,2‐b:4,5‐b']dithiophene‐2,1,3‐benzothiadiazole low‐bandgap polymer

A new heteroarylene‐vinylene donor–acceptor polymer P(BDT‐V‐BTD) with reduced bandgap has been synthesized and its photophysical, electronic and photovoltaic properties investigated both experimentally and theoretically. The structure of the polymer comprises an unprecedented combination of a strong donor (4,8‐dialkoxy‐benzo[1,2‐b:4,5‐b']dithiophene, BDT), a strong acceptor (2,1,3‐benzothiadiazole, BTD) and a vinylene spacer. The new polymer was obtained by a metal‐catalyzed cross‐coupling Stille reaction and fully characterized by NMR, UV–vis absorption, GPC, TGA, DSC and electrochemistry. Detailed ab initio computations with solvation effects have been performed for the monomer and model oligomers. The electrochemical investigation has ascertained the ambipolar character of the polymer and energetic values of HOMO, LUMO and bandgap matching materials‐design rules for optimized organic photovoltaic devices. The HOMO and LUMO energies are consistently lower than those of previous heteroarylene‐vinylene polymer while the introduction of the vinylene spacer afforded lower bandgaps compared to the analogous system P(BDT‐BTD) with no spacer between the aromatic rings. These superior properties should allow for enhanced photovoltages and photocurrents in photovoltaic devices in combination with PCBM. Preliminary photovoltaic investigation afforded relatively modest power conversion efficiencies of 0.74% (AM 1.5G, 100 mW/cm²), albeit higher than that of previous heteroarylene‐vinylene polymers and comparable to that of P(BDT‐BTD). © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Low band‐gap modulation of isoindigo‐based copolymers toward high open‐circuit voltage of polymer solar cells

Designing low band‐gap‐conjugated polymers coupled with low HOMO levels attracts great attention in the field of polymer solar cells (PSCs). By using donor–acceptor (D‐A) copolymerization strategy, we designed and synthesized a series of low band‐gap copolymers with deep HOMO levels via introducing an isoindigo (IID) acceptor unit in the copolymers with the donor unit of fluorene (F) (PIID‐F), carbazole (Cz) (PIID‐Cz), thiophene (Th) (PIID‐Th), dithiophene (DTh) (PIID‐DTh), or dithienosilole (DTS) (PIID‐DTS). The HOMO level of the copolymers, measured by electrochemical cyclic voltammetry, varies from ?5.3 eV to ?5.8 eV, depending on different donor units in the copolymers. However, the LUMO levels of all the copolymers are fixed at about ?3.6 eV, which is mainly determined by IID acceptor unit due to its strong electron‐withdrawing ability. The new results will provide an effect help in designing IID based molecular structures. Among the copolymers, PIID‐DTS has a low band gap of 1.58 eV and possesses a low‐lying HOMO energy level of ?5.33 eV. The PSCs based on PIID‐DTS as donor and PC₇₀BM as acceptor exhibited a high open‐circuit voltage (V_oc) of 0.93 V and a primary power conversion efficiency of 2.45%. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 3477–3485     

Electrochemical and optical properties of novel donor‐acceptor thiophene‐perylene‐thiophene polymers

In this study, donor‐acceptor type thiophene‐perylene‐thiophene monomers were synthesized and polymerized by both oxidative polymerization using FeCl₃ as catalyst and the electrochemical process. UV–vis, FTIR, ¹H NMR, and elemental analysis techniques were used for structural characterization. Thermal behaviors of these compounds were determined by using TGA system. The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels and electrochemical and optical band gap values were calculated by using the results of cyclic voltammetry and UV–vis measurements, respectively. The number–average molecular weight (M_n), weight–average molecular weight (M_w), and polydispersity index (PDI) values of synthesized polymers were determined by size exclusion chromatography. Conductivity measurements of these polymers were carried out by electrometer by using a four‐point probe technique. The conductivity was observed to be increased by iodine doping. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1974–1989, 2008     

Donor–acceptor photovoltaic polymers based on 1,4‐dithienyl‐2,5‐dialkoxybenzene with intramolecular noncovalent interactions

Donor–acceptor (D–A) conjugated polymers bearing non‐covalent configurationally locked backbones have a high potential to be good photovoltaic materials. Since 1,4‐dithienyl‐2,5‐dialkoxybenzene ( TBT ) is a typical moiety possessing intramolecular S…O interactions and thus a restricted planar configuration, it was used in this work as an electron‐donating unit to combine with the following electron‐accepting units: 3‐fluorothieno[3,4‐b]thiophene ( TFT ), thieno‐[3,4‐c]pyrrole‐4,6‐dione ( TPD ), and diketopyrrolopyrrole ( DPP ) for the construction of such D–A conjugated polymers. Therefore, the so‐designed three polymers, PTBTTFT , PTBTTPD , and PTBTDPP , were synthesized and investigated on their basic optoelectronic properties in detail. Moreover, using [6,6]‐phenyl‐C₇₁‐butyric acid methyl ester (PC₇₁BM) as acceptor material, polymer solar cells (PSCs) were fabricated for studying photovoltaic performances of these polymers. It was found that the optimized PTBTTPD cell gave the best performance with a power conversion efficiency (PCE) of 4.49%, while that of PTBTTFT displayed the poorest one (PCE = 1.96%). The good photovoltaic behaviors of PTBTTPD come from its lowest‐lying energy level of the highest occupied molecular orbital (HOMO) among the three polymers, and good hole mobility and favorable morphology for its PC₇₁BM‐blended film. Although PTBTDPP displayed the widest absorption spectrum, the largest hole mobility, and regular chain packing structure when blended with PC₇₁BM, its unmatched HOMO energy level and disfavored blend film morphology finally limited its solar cell performance to a moderate level (PCE: 3.91%). © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 689–698     

Synthesis and characterization of new low band‐gap polymers containing electron‐accepting acenaphtho[1,2‐c]thiophene‐S,S‐dioxide groups

Two donor–acceptor conjugated polymers, PTSSO‐TT and PTSSO‐BDT, composed of acenaphtho[1,2‐c]thiophene ‐ S,S‐dioxide (TSSO) as a new electron acceptor and thienothiophene (TT) or benzo[1,2‐b:4,5‐b']dithiophene (BDT) as electron donors, were synthesized with Stille cross‐coupling reactions. The number‐averaged molecular weights (M_n) of PTSSO‐TT and PTSSO‐BDT were found to be 15100 and 26000 Da, with dispersity of 1.8 and 2.4, respectively. The band‐gap energies of PTSSO‐TT and PTSSO‐BDT are 1.56 and 1.59 eV, respectively. The HOMO levels of PTSSO‐TT and PTSSO‐BDT are ?5.4 and ?5.5 eV, respectively. These results indicate that the inclusion of TSSO accepting units into polymers is a very effective method for lowering their HOMO energy levels. The field‐effect mobilities of PTSSO‐TT and PTSSO‐BDT were determined to be 1.5 × 10^?3 and 4.5 × 10^?4 cm² V^?1 s^?1, respectively. A polymer solar cell device prepared with PTSSO‐TT as the active layer was found to exhibit a power conversion efficiency (PCE) of 3.79% with an open circuit voltage of 0.71 V under AM 1.5 G (100 mW cm^?2) conditions. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 498–506     

Band‐gap engineering of polythiophenes via dithienophosphole doping

A series of polythiophenes doped with dithieno[3,2‐b:2′,3′‐d]phosphole units at varying levels (0–17%) were synthesized and characterized. Polymer work up provided two series of polymers from chloroform (C) and hexanes (H) for each doping level, respectively. Systematic structure–property studies revealed that the C‐series polymers generally had higher molecular weights than the H‐series, but also slightly higher relative dithienophosphole concentrations, both having a significant impact on the photophysical and electrochemical properties of the polymers. Furthermore, the presence of the dithienophosphole units also stabilizes the LUMO levels, whereas the HOMO levels remain dominated by the thiophene units, resulting in desirable electronics for an interaction with acceptor materials, such as 1‐(3‐methoxycarbonyl)propyl‐1‐phenyl[6,6]C₆₁. Importantly, increasing amount of dithienophosphole doping results in increased conductivities for the polymers in their oxidized state, while concurrently significantly stabilizing the neutral polythiophenes toward oxidation under environmental conditions. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis and applications of low‐bandgap conjugated polymers containing phenothiazine donor and various benzodiazole acceptors for polymer solar cells

A series of soluble donor‐acceptor conjugated polymers comprising of phenothiazine donor and various benzodiazole acceptors (i.e., benzothiadiazole, benzoselenodiazole, and benzoxadiazole) sandwiched between hexyl‐thiophene linkers were designed, synthesized, and used for the fabrication of polymer solar cells (PSC). The effects of the benzodiazole acceptors on the thermal, optical, electrochemical, and photovoltaic properties of these low‐bandgap (LBG) polymers were investigated. These LBG polymers possessed large molecular weight (M_n) in the range of 3.85?5.13 × 10⁴ with high thermal decomposition temperatures, which demonstrated broad absorption in the region of 300?750 nm with optical bandgaps of 1.80?1.93 eV. Both the HOMO energy level (?5.38 to ?5.47 eV) and LUMO energy level (?3.47 to ?3.60 eV) of the LBG polymers were within the desirable range of ideal energy level. Under 100 mW/cm² of AM 1.5 white‐light illumination, bulk heterojunction PSC devices containing an active layer of electron donor polymers mixed with electron acceptor [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PC₆₁BM) or [6,6]‐phenyl‐C₇₁‐butyric acid methyl ester (PC₇₁BM) in different weight ratios were investigated. The best performance of the PSC device was obtained by using polymer PP6DHTBT as an electron donor and PC₇₁BM as an acceptor in the weight ratio of 1:4, and a power conversion efficiency value of 1.20%, an open‐circuit voltage (V_oc) value of 0.75 V, a short‐circuit current (J_sc) value of 4.60 mA/cm², and a fill factor (FF) value of 35.0% were achieved. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Benzo[2,1‐b;3,4‐b′]dithiophene‐based low‐bandgap polymers for photovoltaic applications

The synthesis of four alternating copolymers using benzo[2,1‐b;3,4‐b′]dithiophene (BDP) as the common donor unit is presented. Before the synthesis, theoretical calculations that we performed predicted that the incorporation of BDP, which consists of fused dithiophene units with a benzene ring, into these polymers would produce a low‐lying highest occupied molecular orbital (HOMO) energy level. Low‐lying HOMO levels are desirable to produce high open circuit voltages (V_OC) in organic bulk heterojunction (BHJ) photovoltaic devices. The polymers' structural characterization, as well as the preliminary results of their performance in BHJ devices, using (6,6)‐phenyl C₆₁‐butyric acid methyl ester as the electron acceptor, is presented. The V_OC values follow the expected trend: increasing with decreasing HOMO level of the polymer. High V_OC values of 0.81 and 0.82 V have been obtained from two polymers: PBDPBT and PBDPDPP. The initial power conversion efficiency achieved in these unoptimized devices was 1.11% because of relatively low J_SC values. The variation observed in the J_SC values between the four polymers is discussed. Device performance is expected to increase with optimization of processing conditions for the devices. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis of bistriphenylamine‐ and benzodithiophene‐based random conjugated polymers for organic photovoltaic applications

In this study, donor–acceptor random polymers containing benzotriazole acceptor and bistriphenylamine and benzodithiophene donors, P1 and P2 , were successfully synthesized by Stille coupling polymerization. The effect of bistriphenylamine moiety and thiophene π‐conjugated linker on electrochemical, spectroelectrochemical, and optical behaviors of the polymers were investigated. Optoelectronic properties and photovoltaic performance of the polymers were examined under the illumination of AM 1.5G, 100 mW cm^?2. The polymers were characterized by cyclic voltammetry, UV‐Vis‐NIR absorption spectroscopy, gel permeation chromatography. HOMO/LUMO energy levels of P1 and P2 were calculated as ?5.47 eV/–3.41 eV and ?5.43 eV/–3.27 eV, respectively. Bulk heterojunction type solar cells were constructed using blends of the polymers (donor) and [6,6]‐phenyl C₇₁ butyric acid methyl ester (PC₇₁BM) (acceptor). Photovoltaic studies showed that the highest power conversion efficiency of these photovoltaic devices were recorded as 3.50% with open circuit voltage; 0.79 V, short circuit current; 9.45 mA cm^?2, fill factor; 0.53 for P1 :PC₇₁BM (1:2, w/w) in 3% o‐dichlorobenzene (o‐DCB) solution and 3.15% with open circuit voltage; 0.75 V, short circuit current; 8.59 mA cm^?2, fill factor; 0.49 for P2 :PC₇₁BM (1:2, w/w) in 2% chlorobenzene (CB) solution. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 3705–3715     

Synthesis and photovoltaic properties of 2,6‐bis(2‐thienyl) benzobisazole and 4,8‐bis(thienyl)‐benzo[1,2‐B:4,5‐B′]dithiophene copolymers

In an effort to design efficient low‐cost polymers for use in organic photovoltaic cells the easily prepared donor–acceptor–donor triad of a either cis‐benzobisoxazole, trans‐benzobisoxazole or trans‐benzobisthiazole flanked by two thiophene rings was combined with the electron‐rich 4,8‐bis(5‐(2‐ethylhexyl)‐thien‐2‐yl)‐benzo[1,2‐b:4,5‐b′]dithiophene. The electrochemical, optical, morphological, charge transport, and photovoltaic properties of the resulting terpolymers were investigated. Although the polymers differed in the arrangement and/or nature of the chalcogens, they all had similar highest occupied molecular orbital energy levels (?5.2 to ?5.3 eV) and optical band gaps (2.1–2.2 eV). However, the lowest unoccupied molecular orbital energy levels ranged from ?3.1 to ?3.5 eV. When the polymers were used as electron donors in bulk heterojunction photovoltaic devices with PC₇₁BM ([6,6]‐phenyl C₇₁‐butyric acid methyl ester) as the acceptor, the trans‐benzobisoxazole polymer had the best performance with a power conversion efficiency of 2.8%. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 316–324     

Random copolymers based on 3‐hexylthiophene and benzothiadiazole with induced π‐conjugation length and enhanced open‐circuit voltage property for organic photovoltaics

A series of donor‐acceptor low‐bandgap conjugated polymers, that is, HThmBT (m = 3, 6, 9, 12, 15), composed of regioregular 3‐hexylthiophene segments and 2,1,3‐benzothiadiazole units, were synthesized through the Stille coupling polymerization to optimize the π‐conjugation length of the polymer and the intramolecular charge transfer (ICT) effect in the polymer backbone. The polymers had relatively low optical bandgaps ranging from 1.6 to 1.72 eV. Among these polymers, HTh6BT exhibited the best device performance with a power conversion efficiency (PCE) of 1.6%. Moreover, despite being based on thiophene, HTh6BT exhibited a high‐open circuit voltage (V_OC) of over 0.8 V because of its low high occupied molecular orbital (HOMO) energy level. These results provided an effective strategy for designing and synthesizing low‐bandgap conjugated polymers with broad absorption ranges and well‐balanced energy levels. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Controlled self‐assembly of porphyrin/fullerene donor–acceptor complex in a polymer thin film

Thin films composed of polycyclohexane (PCHE), zinc(II)‐5,10,15,20‐tetra‐(2‐naphthyl)porphyrin (ZnTNpP), and [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PCBM) blends are prepared to investigate their potential for the controlled self‐assembly of a porphyrin/fullerene donor–acceptor complex in a polymer thin film. The compatibilities of PCHE/PCBM (p), PCHE/ZnTNpP (q), and ZnTNpP/PCBM (r) in these blends have a significant effect on the dispersion of the ZnTNpP/PCBM donor–acceptor complex in the PCHE thin film. When the compatibilities are p << q, r, and q ≈ r, the ZnTNpP/PCBM donor–acceptor complex is formed between the PCHE and PCBM phases. This concept to form a controlled self‐assembly of the ZnTNpP/PCBM donor–acceptor complex may be applied to various combinations of porphyrin/fullerene systems in polymer thin film solar cells to achieve excellent performance. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 743–746     

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