Hexa-peri-hexabenzocoronene (HBC) is a discotic-shaped conjugated molecule with strong π–π stacking property, high intrinsic charge mobility, and good self-assembly properties. For a long time, however, organic photovoltaic (OPV) solar cells based on HBC demonstrated low power conversion efficiencies (PCEs). In this study, two conjugated terpolymers, poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5′-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT)-5 HBC and PCDTBT-10 HBC, were synthesized by incorporating different amounts of HBC as the third component into poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5′-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT) through Suzuki coupling polymerization. For comparison, the donor–acceptor (D–A) conjugated dipolymer PCDTBT was also synthesized to investigate the effect of HBC units on conjugated polymers. The HBC-containing polymers exhibited higher thermal stabilities, broader absorption spectra, and lower highest-occupied molecular orbital (HOMO) energy levels. In particular, the field-effect mobilities were enhanced by more than one order of magnitude after the incorporation of HBC into the conjugated polymer backbone on account of increased interchain π–π stacking interactions. The bulk heterojunction (BHJ) polymer solar cells (PSCs) fabricated with the polymers as donor and PC₇₁BM as acceptor demonstrated gradual improvement of open-circuit voltage (V_OC) and short-circuit current (J_SC) with the increase in HBC content. As a result, the PCEs were improved from 3.21 % for PCDTBT to 3.78 % for PCDTBT-5 HBC and then to 4.20 % for PCDTBT-10 HBC.

Fullerene bisadducts have emerged as promising electron-accepting materials because of their ability to increase the open-circuit voltage (V_OC) of polymer solar cells (PSCs) due to their relatively high lowest unoccupied molecular orbital (LUMO) energy levels. It should be noted that the as-prepared fullerene bisadducts are in fact a mixture of isomers. Here, the effects of fullerene bisadduct regioisomers on photovoltaic performance are examined. The trans-2, trans-3, trans-4, and e isomers of dihydronaphthyl-based [60]fullerene bisadduct (NCBA) are isolated and used as acceptors for P3HT-based PSCs. The four NCBA isomers exhibit different absorption spectra, electrochemical properties, and electron mobilities, leading to varying PCE values of 5.8, 6.3, 5.6, and 5.5%, respectively, which are higher than that based on an NCBA mixture (5.3%), suggesting the necessity to use the individual fullerene bisadduct isomer for high-performance PSCs.

A series of donor-π-acceptor (D-π-A) conjugated copolymers (PBDT-AT, PDTS-AT, PBDT-TT, and PDTS-TT), based on benzo[1,2-b:4,5-c']dithiophene-4,8-dione (BDD) acceptor unit with benzodithiophene (BDT) or dithienosilole (DTS) as donor unit, alkylthiophene (AT) or thieno[3,2-b]thiophene (TT) as conjugated π-bridge, were designed and synthesized for application as donor materials in polymer solar cells (PSCs). Effects of the donor unit and π-bridge on the optical and electrochemical properties, hole mobilities, and photovoltaic performance of the D-π-A copolymers were investigated. PSCs with the polymers as donor and PC₇₀BM as acceptor exhibit an initial power conversion efficiency (PCE) of 5.46% for PBDT-AT, 2.62% for PDTS-AT, 0.82% for PBDT-TT, and 2.38% for PDTS-TT. After methanol treatment, the PCE was increased up to 5.91%, 3.06%, 1.45%, and 2.45% for PBDT-AT, PDTS-AT, PBDT-TT, and PDTS-TT, respectively, with significantly increased FF. The effects of methanol treatment on the photovoltaic performance of the PSCs can be ascribed to the increased and balanced carrier transport and the formation of better nanoscaled interpenetrating network in the active layer. The results indicate that both donor unit and π-bridge are crucial in designing a D-π-A copolymer for high-performance photovoltaic materials. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 1929–1940

A new two-dimensional conjugated (2D conjugated) and side chain isolated polythiophene derivative with a dodecane carbonyl group terminated triphenylamine-vinylene (CTPA) conjugated side chain and unsubstituted terthiophene spacer, PT4-CTPA, was designed and synthesized. Compared to its polymer analogue of PT2-TPA (with only one thiophene spacer and without the pendant electron-deficient group), the 2D-conjugated and side chain isolated PT4-CTPA with the electron-withdrawing carbonyl group on the conjugated side chain shows a lower lying HOMO (the highest occupied molecular orbital) energy level at –5.24 eV and enhanced absorption of the polymer backbone. A bulk heterojunction polymer solar cell with the polymer as a donor and (6,6)-phenyl C₇₁-butyric acid methyl ester as an acceptor demonstrated a power conversion efficiency (PCE) of 1.56% with an open circuit voltage of 0.7 V under AM1.5G, 100 mW/cm². PCE is more than seven times higher than that of PT2-TPA (0.21%, under same experimental conditions). © 2012 Wiley Periodicals, Inc. Adv Polym Techn 32: E822–E831, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/adv.21324

A series of novel poly(thienylene vinylene) derivatives (PTVs), P20-P24, with imide substituents were designed and synthesized by palladium-catalyzed Stille coupling polymerization, wherein the imide substituent density was decreased gradually, which allowed us to explicitly study the effect of electron-deficient substituent on the optical, electrochemical, and photovoltaic properties of the PTVs. All of the four polymers showed broad absorption bands with optical bandgaps between1.66 and 1.78 eV. By reducing density of electron-deficient imide group, the LUMO energy levels of the polymers could be tuned gradually from −3.75 to −3.43 eV, with HOMO levels upshifted from −5.64 to −5.16 eV. Bulk heterojunction solar cells with the polymers as donor and PC₇₁BM as acceptor demonstrated very different excitons dissociation behavior. With decreasing the imide-fused unit density, the open-circuit voltage (V_OC) values in the devices decreased from 0.78 to 0.62 V, whereas the short-circuit currents (J_SC) increased from 0 to 2.26 mA cm⁻² and then decreased to 1.01 mA cm⁻². By adjusting the electron-withdrawing imide substituent density, power conversion efficiency of the PTVs-based solar cells can be increased to four times, reached 0.86%. To the best of our knowledge, this is the first systematic study of the relationship between molecular energy level and photovoltaic properties of PTVs. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4975–4982

Polymer solar cells (PSCs) have drawn great attention in recent years for their simple device structure, light weight, and low-cost fabrication in comparison with inorganic semiconductor solar cells. However, the power-conversion efficiency (PCE) of PSCs needs to be increased for their future application. The key issue for improving the PCE of PSCs is the design and synthesis of high-efficiency conjugated polymer donors and fullerene acceptors for the photovoltaic materials. For the acceptor materials, several fullerene-bisadduct acceptors with high LUMO energy levels have demonstrated excellent photovoltaic performance in PSCs with P3HT as a donor. In this Focus Review, recent progress in high-efficiency fullerene-bisadduct acceptors is discussed, including the bisadduct of PCBM, indene-C₆₀ bisadduct (ICBA), indene-C₇₀ bisadduct (IC₇₀BA), DMPCBA, NCBA, and bisTOQC. The LUMO levels and photovoltaic performance of these bisadduct acceptors with P3HT as a donor are summarized and compared. In addition, the applications of an ICBA acceptor in new device structures and with other conjugated polymer donors than P3HT are also introduced and discussed.

Two novel porphyrin-based D-A conjugated copolymers, PFTTQP and PBDTTTQP, consisting of accepting quinoxalino[2,3-b′]porphyrin unit and donating fluorene or benzo[1,2-b:4,5-b′]dithiophene unit, were synthesized, respectively via a Pd-catalyzed Stille-coupling method. The quinoxalino[2,3-b′]porphyrin, an edge-fused porphyrin monomer, was used as a building block of D-A copolymers, rather than the simple porphyrin unit in conventional porphyrin-based photovoltaic polymers reported in literature, to enhance the coplanarity and to extend the π-conjugated system of polymer main chains, and consequently to facilitate the intramolecular charge transfer (ICT). The thermal stability, optical, and electrochemical properties as well as the photovoltaic characteristics of the two polymers were systematically investigated. Both the polymers showed high hole mobility, reaching 4.3 × 10⁻⁴ cm² V⁻¹ s⁻¹ for PFTTQP and 2.0 × 10⁻⁴ cm² V⁻¹ s⁻¹ for PBDTTTQP. Polymer solar cells (PSCs) made from PFTTQP and PBDTTTQP demonstrated power conversion efficiencies (PCEs) of 2.39% and 1.53%, both of which are among the highest PCE values in the PSCs based on porphyrin-based conjugated polymers. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013

Over the past two decades, organic semiconductors have been the subject of intensive academic and commercial interests. Thiazole is a common electron-accepting heterocycle due to electron-withdrawing nitrogen of imine (C=N), several moieties based on thiazole have been widely introduced into organic semiconductors, and yielded high performance in organic electronic devices. This article reviews recent developments in the area of thiazole-based organic semiconductors, particularly thiazole, bithiazole, thiazolothiazole and benzobisthiazole-based small molecules and polymers, for applications in organic field-effect transistors, solar cells and light-emitting diodes. The remaining problems and challenges, and the key research direction in near future are discussed.

Polymer solar cells (PSCs) with poly(3-hexylthiophene) (P3HT) as a donor, an indene-C₇₀ bisadduct (IC₇₀BA) as an acceptor, a layer of indium tin oxide modified by MoO₃ as a positive electrode, and Ca/Al as a negative electrode are presented. The photovoltaic performance of the PSCs was optimized by controlling spin-coating time (solvent annealing time) and thermal annealing, and the effect of the spin-coating times on absorption spectra, X-ray diffraction patterns, and transmission electron microscopy images of P3HT/IC₇₀BA blend films were systematically investigated. Optimized PSCs were obtained from P3HT/IC₇₀BA (1:1, w/w), which exhibited a high power conversion efficiency of 6.68%. The excellent performance of the PSCs is attributed to the higher crystallinity of P3HT and better a donor–acceptor interpenetrating network of the active layer prepared under the optimized conditions. In addition, PSCs with a poly(3,4-ethylenedioxy-thiophene):poly(styrenesulfonate) (PEDOT:PSS) buffer layer under the same optimized conditions showed a PCE of 6.20%. The results indicate that the MoO₃ buffer layer in the PSCs based on P3HT/IC₇₀BA is superior to that of the PEDOT:PSS buffer layer, not only showing a higher device stability but also resulting in a better photovoltaic performance of the PSCs.

A novel catalyst-free synthetic strategy for producing high-quality CdTe nanowires in solution is proposed. A special reaction condition is intentionally constructed in the reaction system to induce the formation of nanowires through oriented in situ assembly of tiny particles. To establish such special synthetic conditions in the CdTe system, not only are its typical features and possible solutions deeply analyzed, but also related factors, such as the ligand environment, injection and growth temperature, and Cd-to-Te precursor ratio, are systemically investigated. High-quality ultralong (up to 10 μm) and ultrathin (less than 10 nm) CdTe nanowires are produced in solution under optimal reaction conditions. Morphological, spectral, and compositional analyses are performed to examine the products formed at different reaction stages in order to clarify the formation mechanism of the CdTe nanowires. Furthermore, the transformation of the CdTe nanowires into CdTe/CdSe core–shell heterostructures is intensively explored, and the CdSe epitaxial growth process is specially tracked by morphological and spectral characterization techniques. Finally, CdTe nanowires coated with a continuous and dense CdSe shell are successfully fabricated by using a proper coating protocol.

Two P3HT isomers with branched alkyl side chains, P3EBT and P3MPT, are synthesized. The HOMO energy levels of P3EBT and P3MPT are −5.35 and −5.24 eV, respectively, which are significantly lower than that of P3HT with a linear side chain. The absorption edges of the two P3HT isomer films, especially those of P3EBT, are blue-shifted in comparison with that of P3HT. A PSC based on P3EBT:IC₆₀BA (2:1 w/w) shows a high open-circuit voltage of 0.98 V, which is the highest V_oc reported so far for polythiophene-based PSCs. A PSC based on P3MPT:IC₇₀BA (2:1 w/w) exhibits a power conversion efficiency of 3.62% with a V_oc of 0.91 V. P3MPT is suitable for the application in tandem PSCs.

A donor-acceptor (D-A) copolymer, PDTSDOBT, based on dithienosilole and 5,6-bis(octyloxy)benzo[1,2,5]thiadiazole is synthesized by Pd-catalyzed Stille coupling reaction for application as a donor material in polymer solar cells (PSCs). The polymer shows good thermal stability, strong absorption in the visible region, and a relatively low bandgap of 1.63 eV. The hole mobility of PDTSDOBT as measured by SCLC is 5.58 × 10⁻⁴ cm² V⁻¹ s⁻¹. The power conversion efficiency of a PSC based on PDTSDOBT: PC₇₀BM (1:2 w/w) is 3.51% with a short-circuit current density of 8.96 mA cm⁻², an open-circuit voltage of 0.69 V, and a fill factor of 0.568, under the 100 mW cm⁻² AM1.5G illumination.

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

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

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

Two copolymers of fluorene and thiophene with conjugated side-chain pending acceptor end group of cyanoacetate (P2) and malononitrile (P3) were synthesized. Both polymers exhibit good thermal stability and low highest occupied molecular orbital level (−5.5 eV). In comparison with P2, P3 exhibits stronger UV–vis absorption and higher hole mobility. Polymer solar cells based on P3:PC₇₁BM exhibits a power conversion efficiency of 1.33% under AM 1.5, 100 mW/cm², which is three times of that based on P2:PC₇₁BM. The higher efficiency is attributed to better absorption, higher hole mobility, and the reduced phase separation scale in P3:PC₇₁BM blend. The aggregate domain size in P3:PC₇₁BM blend is 50 nm, much smaller than that in P2:PC₇₁BM blend (200 nm). Tiny difference in the end groups on side chains of P2 and P3 leads to great difference in phase separation scale, charge transport, and efficiency of their photovoltaic devices. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

A series of [6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM)-like fullerene derivatives with the butyl chain in PCBM changing from 3 to 7 carbon atoms, respectively (F1–F5), are designed and synthesized to investigate the relationship between photovoltaic properties and the molecular structure of fullerene derivative acceptors. F2 with a butyl chain is PCBM itself for comparison. Electrochemical, optical, electron mobility, morphology, and photovoltaic properties of the molecules are characterized, and the effect of the alkyl chain length on their properties is investigated. Although there is little difference in the absorption spectra and LUMO energy levels of F1–F5, an interesting effect of the alkyl chain length on the photovoltaic properties is observed. For the polymer solar cells (PSCs) based on P3HT as donor and F1–F5, respectively, as acceptors, the photovoltaic behavior of the P3HT/F1 and P3HT/F4 systems are similar to or a little better than that of the P3HT/PCBM device with power conversion efficiencies (PCEs) above 3.5%, while the performances of P3HT/F3 and P3HT/F5-based solar cells are poorer, with PCE values below 3.0%. The phenomenon is explained by the effect of the alkyl chain length on the absorption spectra, fluorescence quenching degree, electron mobility, and morphology of the P3HT/F1–F5 (1:1, w/w) blend films.

[6, 6]-Phenyl-C₆₁-butyric acid methyl ester (PC₆₀BM) is the widely used acceptor material in polymer solar cells (PSCs). Nevertheless, the low LUMO energy level and weak absorption in visible region are its two weak points. For enhancing the solar light harvest, the soluble C₇₀ derivative PC₇₀BM has been used as acceptor instead of PC₆₀BM in high efficiency PSCs in recent years. But, the LUMO level of PC₇₀BM is the same as that of PC₆₀BM, which is too low for the PSCs based on the polymer donors with higher HOMO level, such as poly (3-hexylthiophene) (P3HT). Here, a new soluble C₇₀ derivative, indene-C₇₀ bisadduct (IC₇₀BA), is synthesized with high yield of 58% by a one-pot reaction of indene and C₇₀ at 180 °C for 72 h. The electrochemical properties and electronic energy levels of the fullerene derivatives are measured by cyclic voltammetry. The LUMO energy level of IC₇₀BA is 0.19 eV higher than that of PC₇₀BM. The PSC based on P3HT with IC₇₀BA as acceptor shows a higher V_oc of 0.84 V and higher power conversion efficiency (PCE) of 5.64%, while the PSC based on P3HT/PC₆₀BM and P3HT/PC₇₀BM displays V_oc of 0.59 V and 0.58 V, and PCE of 3.55% and 3.96%, respectively, under the illumination of AM1.5G, 100 mW cm⁻². The results indicate that IC₇₀BA is an excellent acceptor for the P3HT-based PSCs and could be a promising new acceptor instead of PC₇₀BM for the high performance PSCs based on narrow bandgap conjugated polymer donor.

A donor–acceptor double-cable polythiophene derivative (PT-F1) with side chain containing C₆₀ end group was synthesized, and characterized by infrared, UV-vis absorption and photoluminescence (PL) spectroscopy, and electrochemical cyclic voltammetry. Cyclic voltammogram of PT-F1 shows the oxidation peak of the polymer main chains and the reduction peaks of the C₆₀ end groups, indicating that there is no interaction between the polymer main chains and side chain C₆₀ groups on the ground state. The UV-vis absorption spectrum of PT-F1 film is red-shifted in comparison with that of its chloroform solution. The PL spectrum of the polymer main chain was quenched by the C₆₀ pendant on the side chain. Polymer solar cell with the structure of ITO/PEDOT:PSS/PT-F1/Ca/Al was fabricated. The power conversion efficiency of the device based on PT-F1 reached 0.274% under the illumination of AM 1.5, 100 mW/cm². © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Polymer solar cells (PSCs) have attracted great attention in recent years because of their advantages of easy fabrication, low cost, light weight, and potential for flexible devices. However, the power conversion efficiency (PCE) of the PSCs needs to be improved for future commercial applications. Factors limiting the PCE of the PSCs include the low exploitation of sunlight due to the narrow absorption band of conjugated polymers, and the low charge-transport efficiency in the devices due to the lower charge-carrier mobility of the polymer photovoltaic materials. In this Research News article, recent progress in new conjugated polymer photovoltaic materials fabricated by our group and others is reviewed, including polythiophene (PT) and poly(thienylene vinylene) derivatives with conjugated side chains for a broad absorption band, crosslinked PT derivatives with conjugated bridges for higher hole mobility, and low-bandgap donor–acceptor copolymers for broad, red-shifted absorption to match the solar spectrum.

A donor-π-acceptor (D-π-A) alternative copolymer of carbazole and thieno[3,4b]-pyrazine [P(CZ-TPZ)] is synthesized through a Wittig–Horner reaction. In dilute THF solution, the absorption spectrum of P(CZ-TPZ) shows two absorption peaks at 306 and 452 nm, respectively, and the PL spectrum of the polymer solution displays a PL peak maximum at 543 nm. The polymer possesses relatively high sensitivity and selectivity for Hg²⁺ detection. Upon addition of Hg²⁺ into its THF solution (containing 0.3% CH₃CN), P(CZ-TPZ) exhibits a new absorption peak at 560∼600 nm and its emission was quenched dramatically. The Hg²⁺ detection shows high selectivity in comparison with the other cations of Na⁺, K⁺, Mg²⁺, Ba²⁺, Al³⁺, Cu²⁺, Cd²⁺, Pb²⁺, Ni²⁺, Mn²⁺, and Co²⁺. The Hg²⁺ detection limit of the polymer solution by emission quenching is found to be 1 × 10⁻⁷ mol L⁻¹. P(CZ-TPZ) also shows a selective chromogenic behavior toward Hg²⁺ with color change of the solution from yellow to blue dark which can be detected with the naked eye, the detection limit reaches 1 × 10⁻⁶ mol L⁻¹ with a 1 × 10⁻⁴ mol L⁻¹ polymer solution. The absorption and PL spectral change can be resumed after adding thiourea, therefore the sensing ability of the polymer is re-usable with the treatment of thiourea. The results indicate that P(CZ-TPZ) is a promising chemosensor for the Hg²⁺ detection.

A series of poly(p-phenylene vinylene) (PPV) derivatives with phenylene vinylene side chains (branched PPVs), PPV0, PPV1, PPV2, and PPV3, were synthesized by the Heck coupling reaction and characterized by TGA, absorption spectra, photoluminescence (PL) spectra, and electrochemical cyclic voltammetry. The branched PPVs showed two absorption peaks in the UV–vis region, corresponding to the conjugated side chains (UV absorption) and the main chains (the visible absorption). Especially the absorption spectrum of PPV3 covers a broad wavelength range from 300 to 500 nm. Introducing the electron-donating alkoxy substituents on the PPV main chains and increasing the content of the alkoxy groups lead to bathochromic shift of both absorption and PL spectra from PPV1 to PPV2 to PPV3. The onset oxidation potential of the branched PPVs is lower by 0.1–0.2 V than that of PPV, indicating that the electron-donating ability of the branched PPVs enhanced in comparison with that of PPV. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

A phenylenevinylene-thiophene-phenyleneethynylene copolymer, poly{[1′,4′-bis-(thienyl-vinyl)]-2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylene-vinylene-alt-1,4-dioctyloxyl-phenyleneethynylene}(PTPPV- PPE), was synthesized by the Sonogashira Pd-catalyzed cross-coupling reaction. The copolymer possesses higher thermal decomposition temperature (T_d = 382°C) compared with poly{[1′,4′-bis- (thienyl-vinyl)]-2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylene-vinylene} (PTPPV). The absorption and photoluminescence (PL) peaks of PTPPV-PPE solution and solid film locate in between those of the homopolymers of PTPPV and poly(1,4-dioctyloxyl-phenyleneethynylene) (PPE), and closer to that of PTPPV. Photovoltaic cell was fabricated based on the blend of PTPPV-PPE and PCBM with a weight ratio of 1:1. The primary result shows an open circuit voltage (V_oc) of 0.72 V which is higher than that of the PTPPV (0.67 V), and a power conversion efficiency (PCE) of 0.3% under the illumination of AM1.5, 100 mW/cm² which is much better than that of PPEs. Copyright © 2008 John Wiley & Sons, Ltd.

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