- Synthetic principles directing charge transport in low-band-gap dithienosilole-benzothiadiazole copolymers
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Given the fundamental differences in carrier generation and device operation in organic thin-film transistors (OTFTs) and organic photovoltaic (OPV) devices, the material design principles to apply may be expected to differ. In this respect, designing organic semiconductors that perform effectively in multiple device configurations remains a challenge. Following "donor-acceptor" principles, we designed and synthesized an analogous series of solution-processable π-conjugated polymers that combine the electron-rich dithienosilole (DTS) moiety, unsubstituted thiophene spacers, and the electron-deficient core 2,1,3-benzothiadiazole (BTD). Insights into backbone geometry and wave function delocalization as a function of molecular structure are provided by density functional theory (DFT) calculations at the B3LYP/6-31G(d,p) level. Using a combination of X-ray techniques (2D-WAXS and XRD) supported by solid-state NMR (SS-NMR) and atomic force microscopy (AFM), we demonstrate fundamental correlations between the polymer repeat-unit structure, molecular weight distribution, nature of the solubilizing side-chains appended to the backbones, and extent of structural order attainable in p-channel OTFTs. In particular, it is shown that the degree of microstructural order achievable in the self-assembled organic semiconductors increases largely with (i) increasing molecular weight and (ii) appropriate solubilizing-group substitution. The corresponding field-effect hole mobilities are enhanced by several orders of magnitude, reaching up to 0.1 cm2 V-1 s-1 with the highest molecular weight fraction of the branched alkyl-substituted polymer derivative in this series. This trend is reflected in conventional bulk-heterojunction OPV devices using PC71BM, whereby the active layers exhibit space-charge-limited (SCL) hole mobilities approaching 10-3 cm2 V-1 s-1, and yield improved power conversion efficiencies on the order of 4.6% under AM1.5G solar illumination. Beyond structure-performance correlations, we observe a large dependence of the ionization potentials of the polymers estimated by electrochemical methods on polymer packing, and expect that these empirical results may have important consequences on future material study and device applications.
- Beaujuge, Pierre M.,Tsao, Hoi Nok,Hansen, Michael Ryan,Amb, Chad M.,Risko, Chad,Subbiah, Jegadesan,Choudhury, Kaushik Roy,Mavrinskiy, Alexei,Pisula, Wojciech,Bredas, Jean-Luc,So, Franky,Muellen, Klaus,Reynolds, John R.
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- All-donor poly(arylene-ethynylene)s containing anthracene and silole-based units: Synthesis, electronic, and photovoltaic properties
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The manuscript deals with the synthesis and properties of four new all-donor alternating poly(arylene-ethynylene)s DBSA, DBSTA, DTSA, and DTSTA. The polymers have been obtained by a Sonogashira cross-coupling of 9,10-diethynyl-anthracene with the dibromo-derivatives of 9,9-dioctyl- dibenzosilole (DBSA), 2,7-dithienyl-9,9-dioctyl-dibenzosilole (DBSTA), 4,4-dioctyl-dithienosilole (DTSA), or 2,6-dithienyl-9,9-dioctyl-dithienosilole (DTSTA). The polymers exhibited absorption profiles and frontier orbital energies strongly dependent on their primary structure. Density functional theory calculations confirmed experimental observations and provided an insight into the electronic structure of the macromolecules. In particular, the effects exerted by the thiophene units in DBSTA and DTSTA on the optical properties of the corresponding polymers could be rationalized with respect to DBSA and DTSA. Preliminary photovoltaic measurements have established that the performance of DTSA is among the highest reported for an all-donor polymer. Moreover, UV irradiation of DTSA films under air evidenced a remarkable photostability of this material, providing further evidence that ethynylene-containing electron-rich systems are promising donors for organic solar cells applications.
- Grisorio, Roberto,Suranna, Gian Paolo,Mastrorilli, Piero,Allegretta, Giovanni,Loiudice, Anna,Rizzo, Aurora,Gigli, Giuseppe,Manoli, Kyriaki,Magliulo, Maria,Torsi, Luisa
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- New D-π-A system dye based on dithienosilole and carbazole: Synthesis, photo-electrochemical properties and dye-sensitized solar cell performance
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New donor-linker-acceptor pattern organic dye containing a dithienosilole unit as a π-conjugated system, a carbazole moiety as an electron donor, and a cyanoacrylic acid unit as an electron acceptor was synthesized for application in dye-sensitized solar cell (DSSC). Its photophysical and electrochemical properties were investigated, the dithienosilole unit could dramatically lower the lowest unoccupied molecular orbital (LUMO) level and energy gap. Its performances as sensitizers in solar cells were measured, and possessed a power conversion efficiency of 4.80%.
- Liu, Jie,Sun, Xiang,Li, Zhifang,Jin, Bin,Lai, Guoqiao,Li, Haiying,Wang, Chengyun,Shen, Yongjia,Hua, Jianli
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- Optoelectronic Properties of A-π-D-π-A Thiophene-Based Materials with a Dithienosilole Core: An Experimental and Theoretical Study
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Two A-π-D-π-A thiophene-based small molecules with a central dithienosilole core and dicyanovinyl (DCV) end groups were synthesized. These compounds differ only by the presence of alkyl and alkylsulfanyl chains, respectively, on the thiophene beta positions. Computational data together with the spectroscopic and electrochemical findings (obtained by means of absorption, steady-state/time-resolved emission techniques, and cyclic voltammetry) revealed that both molecules possess low electronic and optical band gaps, broad absorption spectra, and good stability both in p and n-doping states, which make them suitable for optoelectronic applications. In both compounds, the HOMO–LUMO transition involves an intramolecular charge transfer from the electron-donor dithienosilole unit to the two terminal electron-acceptor DCV groups. A marked positive emission solvatochromism was observed for both molecules and was interpreted on the basis of the symmetry breaking in the S1 excited state. The two synthesized compounds were also compared to their shorter precursors and to similar oligothiophenes to understand how the nature of the building block influences the characteristics of the final materials. Furthermore, it was possible to better understand the contribution of the sulfur atom in modulating the optical properties of the small molecules studied.
- Caselli, Monica,Vanossi, Davide,Buffagni, Mirko,Imperato, Manuel,Pigani, Laura,Mucci, Adele,Parenti, Francesca
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- Semiconductor materials prepared from dithienylvinylene copolymers
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Disclosed are new semiconductor materials prepared from dithienylvinylene copolymers with aromatic or heteroaromatic π-conjugated systems. Such copolymers, with little or no post-deposition heat treatment, can exhibit high charge carrier mobility and/or good current modulation characteristics. In addition, the polymers of the present teachings can possess certain processing advantages such as improved solution-processability and low annealing temperature.
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(2016/01/20)
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- New D-π-A system dye based on dithienosilole and carbazole: Synthesis, photo-electrochemical properties and dye-sensitized solar cell performance
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New donor-linker-acceptor pattern organic dye containing a dithienosilole unit as a π-conjugated system, a carbazole moiety as an electron donor, and a cyanoacrylic acid unit as an electron acceptor was synthesized for application in dye-sensitized solar cell (DSSC). Its photophysical and electrochemical properties were investigated, the dithienosilole unit could dramatically lower the lowest unoccupied molecular orbital (LUMO) level and energy gap. Its performances as sensitizers in solar cells were measured, and possessed a power conversion efficiency of 4.80%.
- Liu, Jie,Sun, Xiang,Li, Zhifang,Jin, Bin,Lai, Guoqiao,Li, Haiying,Wang, Chengyun,Shen, Yongjia,Hua, Jianli
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