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Low-band-gap and thermally stable conjugated polymers developed using a dual acceptor–acceptor strategy and the addition of S and F atoms.

The structural rigidity of fused units in the polymer backbone, in addition to the resulting stabilizing effect of the quinoidal structure, and tunable electronic properties have played a key role in promoting highly-ordered π-stacking moieties, exhibiting promising charge carrier mobilities. The electron-deficient thiazole moiety shows high planarity and effective π–π stacking, which leads to the reduction in the energy levels of the highest occupied and lowest unoccupied molecular orbitals (HOMO/LUMO), and ideally enhances the electron charge mobility. Four heterocycle-based monomers BTzS, BTzSe, DTS, and DTG based on fused bithiazole and dithiophene units incorporated with sulfur, selenium, silicon, and germanium as the bridging atoms were synthesized and characterized. The monomers were copolymerized with the electron-rich alkylated thienylenevinylene (TV) unit to afford copolymers P1–P4. The thermal, optical, and electrochemical properties and crystallinity of the copolymers were thoroughly investigated. Extensive OFET device optimization using different solvents and annealing temperatures resulted in the best charge mobility of 0.09 cm2 V−1 s−1 for the electron-deficient bithiazole BTzS copolymer P1 and 0.36 cm2 V−1 s−1 for the DTS copolymer P3.

Conjugated polymers and small molecules (SMs) with fused electron-rich and electron-deficient building blocks are promising materials for low-cost organic electronic devices. Benzotrithiophene (BTT) is one such electron-rich hybrid building block composed of three fused thiophene moieties with an extended π-system that has been widely used to synthesize a variety of electronic materials. Additionally, BTT has a planar and sulfur-rich core with a number of distinct advantages, including structural diversity, tunable electro-optical properties and exceptional hole-transport behavior. So far, four BTT-based isomers have been synthesized on a gram scale from seven isomeric structures, three of which are symmetric (BTT1-3) and one of which is asymmetric (BTT5), for use in a variety of optoelectronic applications. However, no report summarizing the progress of BTT-based semiconductors for electronic applications is available. The current review presents an overview of the recent developments in BTT-based monomers, polymers and SMs, as well as their applications in energy harvesting. Additionally, recent advances on charge transport devices, most notably organic solar cells (OSCs), organic thin field-effect transistors (OTFTs), and perovskite solar cells (Pero-SCs) are also surveyed and summarized. It is anticipated that this comprehensive review will stimulate further research and development of future BTT-based electronic materials, particularly for low-cost and high-performance organic electronic devices.

We report the synthesis and characterization of four novel small bandgap copolymers incorporating the electron-deficient thieno[2,3-d:5,4-d′]bisthiazole and selenopheno[2,3-d:5,4-d′]bisthiazole building blocks with a series of electron-deficient diketopyrrolopyrole units. The four resultant copolymers were synthesized via palladium Stille cross-coupling reaction, and their optical, thermal stability, electrochemical, and field-effect charge transport properties were investigated. All copolymers showed low optical bandgaps (1.53–1.56 eV); in addition, X-ray diffraction on solution-cast films revealed that the selenium-containing copolymers exhibit higher crystallinity compared to their thiophene counterparts.

The three novel acceptor–donor–acceptor (A–D–A) conjugated small molecules were synthesized, each featuring a benzodithiophene (BDT) core presenting lateral flexible side chains: TB-BDT6T substituted with 2-ethynyl-5-octylthiophene, TS-BDT6T substituted with 2-(octylthio)thiophene, and TT-BDT6T substituted with 2-(2-ethylhexyl)thieno[3,2-b]thiophene groups. The lateral incorporation of functionalized π-conjugated flexible side chains, without altering the end-capped acceptor (cyanoacetate) moieties, amended the optoelectronic properties of these BDT-based small molecules. X-ray diffraction spectroscopy revealed that these small molecules possess high crystallinity; moreover, the optimized blend film morphologies, recorded using atomic force microscopy, revealed miscibility with PC61BM, and turn out nanoscale phase separations. The energy levels of the highest occupied and lowest unoccupied molecular orbitals of these small molecules were allowed, leading to high open-circuit voltages (Voc) for their solar...

Herein, we report the design and successful fabrication of new Mg/Fe layered double hydroxides (LDHs) with different Mg/Fe molar ratios (2:1, 3:1, and 4:1) by a coprecipitation method. The prepared Mg/Fe (4:1) LDH sample with high crystallinity and phase purity was further modified by intercalation with molybdate anions. The structural, morphological, optical, electrochemical, and photocatalytic properties of the prepared catalysts were subsequently examined. In comparison with that of the Mg/Fe (4:1) LDH, the photocatalytic activity of the Mg/Fe (4:1) material with molybdate anions intercalated in the interlayer for the degradation of methyl orange (MO) was enhanced, and the processed followed apparent first-order kinetics. Radical-trapping experiments demonstrated that h+, OH· radicals, and O2–· radicals are the dominant reactive species for pollutant degradation. The highest photocatalytic activity of molybdate-intercalated LDH is attributed mainly to the combined effects of its layered structure with MgII–O–FeIII linkages and intercalated molybdate anions, which act as visible-light absorption centers towards higher wavelengths and can promote charge-carrier trapping as well as hinder the photogenerated electron–hole recombination. The time-resolved photoluminescence (TRPL) spectra demonstrated the prolonged charge separation under visible light.

New low band gap copolymers P1–P4, based on thienylenevinylene (TV) and pyrrolo[3,2-d:4,5-d′]bisthiazole (PBTz) units composed of different alkyl side chains, such as 2-octyldodecyl (OD), n-hexadecyl (HD), 2-ethylhexyl (EH), and 9-heptadecyl (HD) groups, respectively, have been synthesized and characterized. Electrochemical and optical studies of the copolymers indicated low energy band gaps in the range of 1.40–1.47 eV. Moreover, theoretical calculation with density functional theory (DFT) and time-dependent DFT calculations demonstrated that the energy band gaps, HOMO energy levels and maximum absorption values in the copolymers were in good agreement with the experimental results. The decomposition temperature of all copolymers was measured to be above 340 °C by thermogravimetric analysis (TGA), which indicates high thermal stability. Thermally annealed OTFT devices based on P1–P4 thin films demonstrated a range of hole mobilities; thus, the P2 based OTFT device exhibited the highest hole mobility of 0.062 cm2 V−1 s−1.

Novel low band gap polymers based on pyrrolo[3,2-d:4,5-d′]bisthiazole (PBTz) and thienylenevinylene (TV) For Organic Electronic Applications Dhananjaya Patra?,1 Hassan S. Bazzi,1 Lei Fang¬2 and Mohammed Al-Hashimi1 1Department of Chemistry, Texas A&M University at Qatar, P.O. Box 23874, Doha, Qatar 2Department of Chemistry and Department of Materials Science and Engineering, Texas A&M University, College Station, TX. Corresponding author: dhananjaya.patra@qatar.tamu.edu π-Conjugated organic polymers have been intensively studied over the past two decades due to their potential applications in areas such as organic light-emitting diodes (OLEDs),1 organic thin-film transistors (OTFTs), organic photovoltaics (OPV), and organic laser devices. In addition, they possess excellent properties that enable them to be solution processed offering a path-way for fabrication on large-area printable and cost-effective flexible electronic devices. Several donor-acceptor (D-A) conjugated polymers and small molecules are reported recently with photovoltaic performance over 12%.2-4 Recently significant development has been made in the design and synthesis of high performance polymers with mobilities now easily surpassing μ > 1 cm2 V-1 s-1.5 Among the various conjugated electron-donating building blocks, thienylenevinylene (TV) unit has attracted much interest owing to its coplanarity and extended π-conjugation which are induced by the presence of a vinylene spacer between the two thiophene units. As a result this enhanced interchain interaction the polymers exhibit a higher hole mobility and reduced energy band gaps.4 Recently, the incorporation of vinylene unit into several electron-rich (i.e., donor) and electron deficient (i.e., acceptor) units has been widely studied, especially, targeting at the device application for n-channel and ambipolar OTFTs with promising device performance. Among these units are diketopyrrolopyrrole (DPP), benzoselenadiazole (BSe), phthalimide (PhI), naphthalenediimide (NDI), benzothiadiazole (BT), dithienothiophene (DTT), thienopyrroledione (TPD), and isoindigo (iI) as depicted in Figure 1. For instance, Yoo et al. reported the synthesis of various polymers based on DPP and (E)-2-(2-(thiophen-2-yl)-vinyl)thiophene units by altering the number of thiophene in the repeat unit to induce strong π–π stacking and favorable molecular conformation. By replacing the thiophene unit with the selenophene vinylene selenophene Kang et al. reported an enhanced mobility. Several DPP and TV based polymers reported by Oh and Kim et al. via various side-chain engineering on the DDP units, obtained remarkable mobilities from 8.74 to 17.8 cm2 V − 1 s − 1.5 Reichmanis and co-workers also reported the synthesis of a series of BT oligothiophene and oligo-TV donor-acceptor (D − A) copolymers exhibiting mobilities of up to 0.75 cm2 V − 1 s − 1. Kim and co-workers reported the synthesis and characterization of highly soluble poly(thienylenevinylene) exhibiting carrier mobility of 1 cm2 V − 1 s − 1.6 Al-Hashimi, Heeney and co-workers systematically investigated the role of modifying the heteroatom, by synthesizing a series of vinylene copolymers containing 3-dodecylthiophene, selenophene and tellurophene.7,8 Figure 1. Structures of thiophene (Th), thiazole (Tz) diketopyrrolopyrrole (DPP), benzoselenadiazole (BSe), phthalimide (PhI), naphthalenediimide (NDI), benzothiadiazole (BT), dithienothiophene (DTT), thienopyrroledione (TPD), and isoindigo (iI). Another particularly promising class of building block for the development of high performing polymeric semiconductors for OTFTs is the electron-deficient pyrrolo[3,2-d:4,5-d′]bisthiazole (PBTz)-based heterocycle. In comparison to dithienothiophene (Figure 1), PBTz-unit is a weak acceptor having an electronegative nitrogen atom, which lowers the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energies. Therefore, it is expected that the large polarity of the thiazole ring can enhance the intermolecular interaction. In addition, the bridging nitrogen (N) of PBTz offers the opportunity to include an additional solubilizing sidechain, which is not present in the analogous DTT. This potentially offer improved solubility and processability of the polymers. Nonetheless, to the best of our knowledge, there is no single report on the synthesis, polymer characterization, and charge carrier transport properties employing the fused PBTz containing TV units. In this work, we report the synthesis and characterization of a series of four PBTz-TV-based copolymers P1-P4 (Scheme 2) with various alkyl side chains for OTFT applications. Particularly, we have selected a dodecyl alkyl side chain on the thienylenevinylene unit, three branched alkyl side chains such as 2-octyldodecyl (OD), 9-heptadecyl (HD) and 2-ethylhexyl (EH), and a long straight n-hexadecyl (HD) chain on the nitrogen of the pyrrolobisthiazole unit, thus, for improving polymer solubility and effectively to promote π − π interchain interactions. The electrochemical redox properties and related electronic structures (HOMO/LUMO energy levels) were systematically investigated by cyclic voltammetry (CV). In addition, the microstructure and morphology of the polymer thin films were characterized by atomic force microscopy (AFM) and X-ray diffraction (XRD). Finally, the PBTZ-copolymers show band gaps in the range of 1.40 − 1.46 eV and mobilities in the range of 0.002-0.062 cm2 V − 1 s − 1 in bottom-gate/top-contact OTFTs.9 References. 1. Burroughes, J. H.; Bradley, D. D. C.; Brown, A. R.; Marks, R. N.; Mackay, K.; Friend, R. H.; Burn, P. L.; Holmes, A. B. Nature, 1990, 347, 539. 2. Sekitani, T.; Zschieschang, U.; Klauk, H.; Someya, T. Nat. Mater.,2010, 9, 1015.3. Zhao, W.; Li, S.; Yao, H.; Zhang, S.; Zhang, Y.; Yang, B.; Hou, J. J. Am. Chem. Soc., 2017, 139, 7148. 4. Li, N.; Baran, D.; Forberich, K.; Machui, F.; Ameri, T.; Turbiez, M.; Carrasco-O., M.; Drees, M.; Facchetti, A.; Krebse, F.C.; Brabec, C. J. Energy Environ. Sci., 2013, 6, 3407. 5. Kim, J.; Lim, B.; Baeg, K. J.; Noh, Y. Y.; Khim, D.; Jeong, H. G.; Yun, J. M.; Kim, D. Y. Chem. Mater.,2011, 23, 4663. 6. Fu, B. Y.; Baltazar, J.; Hu, Z. K.; Chien, A. T.; Kumar, S.; Henderson, C. L.; Collard, D. M.; Reichmanis, E. Chem. Mater.,2012, 24, 4123 7.Al-Hashimi, M.; Han, Y.; Smith, J.; Bazzi, H. S.; Alqaradawi, S. Y. A.; Watkins, S. E.; Anthopoulos, T. D.; Heeney, M. Chem. Sci.,2016, 7, 1093. 8. Al-Hashimi, M.; Baklar, M. A.; Colleaux, F.; Watkins, S. E.; Anthopoulos, T. D.; Stingelin, N.; Heeney, M. Macromolecules, 2011, 44, 5194. 9. Patra, D.; Lee, J.; Lee, J.; Sredojevic, D. N.; White, A.J.P.; Bazzi, H. S.; Brothers, E. N.; Heeney, M.; Fang, L.; Yoon. M.-H.; Al-Hashimi, M. J. Mater. Chem. C., 2017, 5, 2247.

In this study we used simultaneous grazing-incidence small- and wide-angle X-ray scattering (GISAXS and GIWAXS, respectively) to probe the multilength-scale structures of thin active layers comprising the linear A–D–A-type π-conjugated donor molecule TBDTCNR and the fullerene acceptor molecule PC61BM for use in solution-processed small-molecule-based organic solar cells (SMOSCs). We found that the pseudo-two-dimensional fractal-like networks in the bulk heterojunction (BHJ) structure were determined by mutual interactions between the small-molecule (SM) crystallites and the nanoscale PC61BM clusters during their formation and phase separation, and deduced quantitatively, at multiple length scales, the BHJ structures comprising these SM crystallites and PC61BM clusters. We also conducted in situ GIWAXS measurements to study the temporal behavior and kinetics of SM crystallization from solution to the solid film state. Our GISAXS/GIWAXS study revealed that the multilength-scale BHJ structures in the thin fi...

Ternary bulk heterojunctions (BHJs) are platforms that can improve the power conversion efficiencies of organic solar cells. In this paper, we report an all-small-molecule ternary BHJ solar cell incorporating [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) and indene-C60 bisadduct (ICBA) as mixed acceptors and the conjugated small molecule (2Z,2′E)-dioctyl 3,3′-(5′′,5′′′′′-(4,8-bis(5-octylthiophen-2-yl)benzo[1,2-b:5,4-b′]dithiophene-2,6-diyl)bis(3,4′,4′′-trioctyl-[2,2′:5′,2′′-terthiophene]-5′′,5-diyl))bis(2-cyanoacrylate) (BDT6T) as a donor. When incorporating a 15% content of ICBA relative to PC71BM, the ternary BHJ solar cell reached a power conversion efficiency of 6.36% with a short-circuit current density (JSC) of 12.00 mA cm−2, an open-circuit voltage (VOC) of 0.93 V, and a fill factor of 0.57. The enhancement in efficiency, relative to that of the binary system, resulted mainly from the increased value of JSC, attributable to not only the better intermixing of the donor and acceptor that improved charge transfer but also the more suitable morphology for efficient dissociation of excitons and more effective charge extraction. Our results suggest that there is great potential for exceeding the efficiencies of binary solar cells by adding a third component, without sacrificing the simplicity of the fabrication process.

In this study, we have strategically designed and convergently synthesized two novel, symmetrical, and linear A-D-A-type π-conjugated donor molecules (TBDTCNR, TBDTCN), each containing a planar electron-rich 2-octylthiene-5-yl-substituted benzodithiophene (TBDT) unit as the core, flanked by octylthiophene units and end-capped with electron-deficient cyanoacetate (CNR) or dicyanovinyl (CN) units. We thoroughly characterized both of these materials and investigated the effects of the end groups (CNR, CN) on their optical, electrochemical, morphological, and photovoltaic properties. We then fabricated solution-processed bulk heterojunction organic solar cells incorporating TBDTCNR and TBDTCN. Among our tested devices, the one containing TBDTCNR and [6,6]-phenyl-C61-butyric acid methyl ester in a 1:0.40 ratio (w/w) exhibited the highest power conversion efficiency (5.42%) with a short-circuit current density (Jsc) of 9.08 mA cm(-2), an open circuit voltage (Voc) of 0.90 V, and an impressive fill factor (FF) of 0.66 under AM 1.5G irradiation (100 mW cm(-2)). The FFs of these solution-processed small-molecule organic solar cells (SMOSCs) are outstanding when compared with those recently reported for benzodithiophene (BDT)-based SMOSCs, because of the high crystallinity and excellent stacking properties of the TBDT-based compounds.

Global environmental and resource concerns dictate that future energy supply and security will become increasingly dependent upon the development of accessible, sustainable and scalable energy technologies. State-of-art polymer solar cells (PSCs) has been considered as one of the renewable important technologies which can harvest solar energy from sunlight to generate electricity. Intensive research efforts from both academia and industry have been dedicated into solution-processed organic solar cells due to development of the next-generation solar cells technology 1,2. Owing to the readily available carbon feedstock as well as the numerous and flexible synthetic pathways, polymer solar cells (PSCs) gained tremendous attentions over silicon solar cell in the past decay due to low- cost and quick energy pay-back, solution-processable, lightweight, and flexible/stretchable, large area photovoltaic panels. 1,2 So as to achieve the high performance solar cells it is very important to develop novel kinds of active materials, which have to cover entire solar spectrum i.e. from ultraviolet to infrared (IR) regions, suitable molecular energy levels morphologies and high mobilities. Several donor-acceptor (D-A) conjugated polymers are reported recently with photovoltaic performance over 10%. 3 However, in D-A PSC materials have high intrinsic torsional defects, which impacts the negative impact on performance of the OPV devices. The torsional defects partially break the conjugation pathways of the polymers, leading to shortened coherent lengths along the polymer chain and decreased carrier mobilities. Meanwhile, the torsional defects perturb the intermolecular packing of the polymer materials so that the electronic coupling between the polymer chains are interrupted, adding an energy barrier for the charge carriers and excitons to transport within the active layer. 4 Moreover, the torsional defects increase the band gap of conjugated polymers, hence to prevent their photo-absorption in longer wavelength region. Overall the torsional defects often lead to larger π–π stacking distances in the polymer thin film, making the thin film more susceptible to the permeation of oxygen and water, hence decreasing the stability of the overall OPV devices. Our approach looks into ways to overcome the drawbacks raised by torsional defects on a fundamental level. By definition, Ladder polymers consist of cyclic subunits, connected to each other by two links that are attached to different sites of the respective subunits, comparable to a graphene nanoribbon. Consequently, ladder polymers have two or more independent strands of bonds which are tied together regularly without merging to a single or double bond or crossing each other. 4 As a result, ladder polymers have large planar core structures with no torsional defects. Such defect-free feature grants them with rigid and hence highly conjugated core structures. On one hand, the highly conjugated cores not only afford low band gaps that allow strong optical absorption at long wavelength in terms of energy absorption, but also lead to low beta value for coherent tunneling and low activation energy for electron hopping, in terms of charge transport alongside the polymer chains. There were many carbazole-containing organic D-A polymer materials has been demonstrated for high performance solar cell applications and no such types of ladder polymers reported by utilizing carbazole core. 5 Herein, we report the synthesis of fully conjugated carbazole-based ladder polymer with low level of unreacted defects, by utilizing the controlled ring-closing olefin metathesis (RCM) reaction. The designed ladder polymer is well soluble in common organic solvents for solution processability. We also discussed the photo-physical, electrochemical and optoelectronic properties of torsional defect-free ladder polymers.References[1] L. Lu, T. Zheng, Q. Wu, A. M. Schneider, D. Zhao, L. Yu, Chem. Rev. 2015, DOI: 10.1021/acs.chemrev.5b00098.[2] L. Dou, Y. Liu, Ziruo Hong, Gang Li, Y. Yang, Chem. Rev. 2015, DOI: 10.1021/acs.chemrev.5b00165.[3] J-D. Chen, C. Cui, Y.-Q. Li, L. Zhou, Q.-D. Ou, C. Li, Y. Li, J.-X. Tang, Adv. Mater. 2015, 27, 1035.[4] A.-D. Schluter Adv. Mater. 1991, 3, 283.[5] J. Lee, B. B. Rajeeva, T. Yuan, Z. Guo, Y. Lin, M. Al-Hashimi, Y. Zheng and L. Fang, Chem. Sci., 2015, DOI: 10.1039/C5SC02385H.

In this study two series of novel symmetrical acceptor–donor–acceptor organic sensitizers containing 3,6- and 2,7-functionalized carbazole cores, respectively, connected to two anchoring cyanoacrylic acid termini via thienyl linkers were synthesized. The effect of the molecular planarity originating from the 3,6- and 2,7-functionalized carbazole cores on the performance of corresponding solar cells were investigated. Molecular orbital analyses revealed the characteristics of the carbazole-based highest occupied molecular orbitals and acid-based lowest unoccupied molecular orbitals. Time-dependent density functional theory calculations allowed us to assign the electronic transitions (>90%) of the low energy bands. Among these new dyes, the highest power conversion efficiency of 4.82% was obtained in a dye-sensitized solar cell device under standard AM 1.5 sunlight with an open-circuit voltage of 0.61 V, a short-circuit photocurrent density of 12.66 mA cm−2 and a fill factor of 0.62.

Stille polymerization was employed to synthesize a low-band-gap (LBG) conjugated main-chain polymer PBTH consisting of bithiazole, dithieno[3,2-b:2′,3′-d]pyrroles (DTP), and pendent melamine derivatives. Novel supramolecular polymer networks PBTH/C and PBTH/F were developed by mixing proper molar amounts of polymer PBTH (containing melamine pendants) to be hydrogen-bonded (H-bonded) with complementary uracil-based conjugated cross-linkers C and F (i.e., containing two symmetrical uracil moieties connected with carbazole and fluorene units through triple bonds). The formation of multiple H-bonds between polymer PBTH and cross-linkers C or F was confirmed by FT-IR measurements. In contrast to polymer PBTH , the supramolecular design with multiple H-bonds can enhance the photovoltaic properties of polymer solar cell (PSC) devices containing H-bonded polymer networks PBTH/C and PBTH/F by tuning their light harvesting capabilities, HOMO energy levels, and crystallinities. Initially, the power conversion efficiency (PCE) values of PSC devices containing supramolecular polymer networks PBTH/C and PBTH/F as electron donors and [6,6]-phenyl-C 71 -butyric acid methyl ester (PC 70 BM) as an electron acceptor (polymer:PC 70 BM = 1:1 w/w) are found to be 0.97 and 0.68%, respectively, in contrast to 0.52% for polymer PBTH . The highest PCE value of 1.56% with a short-circuit current densities ( J sc ) value of 7.16 mA/cm 2 , a open circuit voltages ( V oc ) value of 0.60 V, and a fill factor (FF) of 0.36 was further optimized in the PSC device containing a supramolecular polymer network PBTH/C as polymer:PC 70 BM = 1:2 w/w. These results indicate that supramolecular design is an effective route towards better photovoltaic properties of V oc , J sc , and PCE values in polymer solar cells.

Two random (Zn(II)-based P1-P2) and two alternating (Ru(II)-based P3-P4) metallo-copolymers containing bis-terpyridyl ligands with various central donor (i.e., fluorene or carbazole) and acceptor (i.e., benzothiadiazole) moieties were synthesized. The effects of electron donor-acceptor interactions with metal (Zn(II) and Ru(II)) ions on their thermal, optical, and electrochemical properties were investigated. Because of the strong ICT transitions between donor and acceptor ligands in both Zn(II)- and Ru(II)-based metallo-coplymers and MLCT transitions in Ru(II)-based metallo-coplymers, the absorption spectra covered a broad range of 260-750 nm with the band gaps of 1.57-1.77 eV. In addition, the introduction of Ru(II)-based metallo-coplymer P4 mixed with PC(60)BM as an active layer of the BHJ solar cell device exhibited the highest PCE value up to 0.90%.

A conjugated main-chain copolymer (PBT) consisting of bithiazole, dithieno[3,2-b:2′,3′-d]pyrroles (DTP), and pendent melamine units was synthesized by Stille polymerization, which can be hydrogen-bonded (H-bonded) with proper molar amounts of bi-functional π-conjugated crosslinker F (i.e., two uracil motifs covalently attached to a fluorene core through triple bonds symmetrically) to develop a novel supramolecular polymer network (PBT/F). The effects of multiple H-bonds on light harvesting capabilities, HOMO levels, and photovoltaic properties of polymer PBT and H-bonded polymer network PBT/F are investigated. The formation of supramolecular polymer network (PBT/F) between PBT and F was confirmed by FTIR and XRD measurements. Because of the stronger light absorption, lower HOMO level, and higher crystallinity of H-bonded polymer network PBT/F, the solar cell device containing PBT/F showed better photovoltaic properties than that containing polymer PBT. The preliminary results show that the solar cell device containing 1:1 weight ratio of PBT/F and [6,6]-phenyl C71 butyric acid methyl ester (PC71BM) offers the best power conversion efficiency (PCE) value of 0.86% with a short-circuit current density (Jsc) of 4.97 mA/cm2, an open circuit voltage (Voc) of 0.55 V, and a fill factor (FF) of 31.5%. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Five conjugated LBG polymers P1–P5 consisting of a DTP unit as an electron donor and various bithiazole units as electron acceptors are designed and synthesized for photovoltaic applications. The effects of the electron-deficient bithiazole derivatives on the thermal, optical, electrochemical, and photovoltaic properties are investigated. The molecular structures are confirmed and characterized. The resulting polymers have high thermal stabilities and broad absorption bands with low optical bandgaps. The hole and electron mobilities are calculated. PSC devices are fabricated utilizing the polymers as electron donors and PCBM as an electron acceptor. The PSC device with an active layer of P4:PCBM (1:1 by weight) exhibits the best power-conversion efficiency.

Two b-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 proper- ties 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

A series of π-conjugated bis-terpyridyl ligands (M1–M3) bearing various benzodiazole cores and their corresponding main-chain Ru(II) metallo-polymers were designed and synthesized. The formation of metallo-polymers were confirmed by NMR, relative viscosity, and UV-visible titration measurements. The effects of electron donor and acceptor interactions on their thermal, optical, electrochemical, and photovoltaic properties were investigated. Due to the strong intramolecular charge transfer (ICT) interaction and metal to ligand charge transfer (MLCT) in Ru(II)-containing polymers, the absorption spectra covered a broad range of 260–750 nm with the optical band gaps of 1.77–1.63 eV. In addition, due to the broad sensitization areas of the metallo-polymers, their bulk heterojunction (BHJ) solar cell devices containing [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) as an electron acceptor exhibited a high short-circuit current (Jsc). An optimum PVC device based on the blended polymer P1:PCBM = 1:1 (w/w) achieved the maximum power conversion efficiency (PCE) value up to 0.45%, with Voc = 0.61 V, Jsc = 2.18 mA cm−2, and FF = 34.1% (under AM 1.5 G 100 mW cm−2), which demonstrated a novel family of conjugated polyelectrolytes with the highest PCE value comparable with BHJ solar cells fabricated from ionic polythiophene and C60.

Four novel symmetrical organic dyes (S1–S4) configured with acceptor–donor–acceptor (A–D–A) structures containing electron donating fluorene (S1 and S2) and N-alkyl dithieno[3,2-b:2′,3′-d]pyrrole (DTP) (S3 and S4) cores terminated with two anchoring cyanoacrylic acids (as electron acceptors) were synthesized and applied to dye-sensitized solar cells (DSSCs). The DSSC device based on S2 dye showed the best photovoltaic performance among S1–S4 dyes: a maximum monochromatic incident photon-to-current conversion efficiency (IPCE) of 76%, a short circuit current (JSC) of 12.27 mA/cm2, an open circuit voltage (VOC) of 0.61 V, a fill factor (FF) of 0.63, and an overall power conversion efficiency (η) of 4.73%. Besides, the utilization of chenodoxycholic acid (CDCA) as a co-adsorbent in the DSSC device based on S3 dye showed a significant improvement in its η value (from 3.70% to 4.31%), which is attributed to the suppression of dye aggregation on TiO2 surface and thus to increase the JSC value eventually.

A series of novel hydrogen-bonded (H-bonded) cross-linking polymers were generated by complexing various proton-donor (H-donor) solar cell dyes containing 3,6- and 2,7-functionalized electron-donating carbazole cores bearing symmetrical thiophene linkers and cyanoacrylic acid termini with a proton-acceptor (H-acceptor) side-chain homopolymer carrying pyridyl pendants (with 1/2 M ratio of H-donor/H-acceptor). The supramolecular H-bonded structures between H-donor dyes and the H-acceptor side-chain polymer were confirmed by FTIR measurements. The effects of the supramolecular architecture on optical, electrochemical, and organic photovoltaic (OPV) properties were investigated. From DFT (density functional theory) calculations, the optimized geometries of organic dyes reflected that the carbazole cores of H-donor dyes were coplanar with the conjugated thiophenes and cyanoacrylic acids, which is essential for strong conjugations across the donor-acceptor units in D1–D4 dyes. Under 100 mW/cm2 of AM 1.5 white-light illumination, bulk heterojunction (BHJ) OPV cell devices containing an active layer of H-bonded polymers (PDFTP/D1–D4) as an electron donor blended with [6,6]-phenyl C61-butyric acid methyl ester (PCBM) as an electron acceptor in a weight ratio of 1:1 were explored. From the preliminary investigations, the OPV device containing 1:1 weight ratio of H-bonded polymer PDFTP/D2 and PCBM showed the best power conversion efficiency (PCE) value of 0.31% with a short-circuit current (Jsc) of 1.9 mA/cm2, an open-circuit voltage (Voc) of 0.55 V, and a fill factor (FF) of 29%, which has a higher PCE value than the corresponding H-donor D2 dye (PCE = 0.15%) or H-acceptor PDFTP homopolymer (PCE = 0.02%) blended with PCBM in 1:1 weight ratio.

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 poly- mer solar cell applications. The polymers covered broad absorption spectra of 400-800 nm with narrow optical band- gaps ranging 1.66-1.72 eV. The highest occupied molecular or- bital 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/cm 2 of AM 1.5 white-light illumination, bulk heterojunction photovoltaic devices composing of an active

A series of low-band-gap (LBG) donor-accepor con- jugated main-chain copolymers (P1-P4) containing planar 2,7- carbazole as electron donors and bithiazole units (4,4 0 -dihexyl- 2,2 0 -bithiazole and 4,4 0 -dihexyl-5,5 0 -di(thiophen-2-yl)-2,2 0 -bithia- zole) as electron acceptors were synthesized and studied for the applications in bulk heterojunction (BHJ) solar cells. The effects of electron deficient bithiazole units on the thermal, optical, electrochemical, and photovoltaic (PV) properties of these LBG copolymers were investigated. Absorption spectra revealed that polymers P1-P4 exhibited broad absorption bands in UV and visible regions from 300 to 600 nm with opti- cal band gaps in the range of 1.93-1.99 eV, which overlapped with the major region of the solar emission spectrum. More- over, carbazole-based polymers P1-P4 showed low values of the highest occupied molecular orbital (HOMO) levels, which provided good air stability and high open circuit voltages (Voc) in the PV applications. The BHJ PV devices were fabricated using polymers P1-P4 as electron donors and (6,6)-phenyl-C61- butyric acid methyl ester (PC61BM) or (6,6)-phenyl-C71-butyric acid methyl ester (PC71BM) as electron acceptors in different weight ratios. The PV device bearing an active layer of polymer blend P4:PC71BM (1:1.5 w/w) showed the best power conver- sion efficiency value of 1.01% with a short circuit current den- sity (Jsc) of 4.83 mA/cm 2 , a fill factor (FF) of 35%, and Voc ¼ 0.60 V under 100 mW/cm 2 of AM 1.5 white-light illumination.

A series of soluble donor-acceptor conjugated poly- mers comprising of phenothiazine donor and various benzodia- zole 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 photo- voltaic properties of these low-bandgap (LBG) polymers were investigated. These LBG polymers possessed large molecular weight (Mn) in the range of 3.85� 5.13 � 10 4 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/cm 2 of AM 1.5 white-light illumination, bulk heterojunction PSC devices containing an active layer of elec- tron donor polymers mixed with electron acceptor (6,6)-phe- nyl-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 do- nor 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 (Voc) value of 0.75 V, a short-circuit current (Jsc) value of 4.60 mA/cm 2 , and a fill factor (FF) value of 35.0% were achieved. V C 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 4823-4834, 2010

In this study, we combined two small-molecule donors-a diketopyrrolopyrrole-based small molecule (SMD) and a benzodithiophene-based molecule (BDT6T)-with [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) to form ternary blend solar cells. The power conversion efficiency of the binary SMD:PC61BM bulk heterojunction solar cell improved from 4.57 to 6.28% after adding an appropriate amount BDT6T as a guest. We attribute this 37% improvement in device performance to the complementary absorption behavior of BDT6T and SMD, as evidenced by the increase in the short circuit current. After addition of BDT6T to form the ternary blend, the crystallinity and morphology of the active layer were enhanced. For example, the features observed in the ternary active layers were finer than those in the binary blends. This means that BDT6T as a third component in the ternary blend has effective role on both the absorption and the morphology. In addition, adding BDT6T to form the ternary blend also led to an increase in the open-circuit voltage. Our findings suggest that the preparation of such simple all-small-molecule ternary blends can be an effective means of improving the efficiency of photovoltaic devices.

In this study we used convergent syntheses to prepare two novel acceptor–donor–acceptor (A–D–A) small molecules (BT4OT, BT6OT), each containing an electron-rich benzotrithiophene (BT) unit as the core, flanked by octylthiophene units, and end-capped with electron-deficient cyanoacetate units. The number of octylthiophene units affected the optical, electrochemical, morphological, and photovoltaic properties of BT4OT and BT6OT. Moreover, BT4OT and BT6OT possess low-energy highest occupied molecular orbitals (HOMOs), providing them with good air stability and their bulk heterojunction (BHJ) photovoltaic devices with high open-circuit voltages (Voc). A solar cell device containing BT6OT and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) in a 1:0.75 ratio (w/w) exhibited a power conversion efficiency (PCE) of 3.61% with a short-circuit current density (Jsc) of 7.39 mA cm−2, a value of Voc of 0.88 V, and a fill factor (FF) of 56.9%. After adding 0.25 vol% of 1-chloronaphthalene (CN) as a processing additive during the formation of the blend film of BT6OT:PC71BM (1:0.75, w/w), the PCE increased significantly to 5.05% with values of Jsc of 9.94 mA cm−2, Voc of 0.86 V, and FF of 59.1% as a result of suppressed nanophase molecular aggregation.