Tuneable optical gain and broadband lasing driven in electrospun polymer fibers by high dye concentration

The optical gain of blue light-emitting electrospun polystyrene fibers doped with a linear multi-fragment molecular dye based on the combination of fluorine-carbazole functional units is investigated, with the aim of correlating emission properties and the specific material architecture made of either aligned or disordered fibers. Enhanced performance is found in aligned fibers, whose gain spectrum can be finely tuned by varying the dye concentration. Instead, randomly oriented fibers show a manifold spectral line narrowing, resulting in sharp laser peaks superimposed on top of a broad emission band, ascribable to random lasing. In these systems, the increase of the dye content turns out to be effective for both decreasing the lasing threshold by about a factor of 6 and for varying the laser emission wavelength. These results make these arrays and disordered architectures of fibers valuable active media for variable-gain, broadband lasing, which is remarkably important in optical sensing and tunable microlaser devices

Comparative study of 2,7 versus 3,6 disubstituted carbazole as hole transporting materials in solid state DSSC

International audienceA comparative study of thermal and electrochemical properties of 2,7 and 3,6 disubstituted carbazole is presented and their performances were compared in solid state Dye Sensitized Solar Cell (DSSC). Although the two compounds possess similar glass transition temperature of 100°C, their electrochemical behaviors are quite different. HOMO energy levels have been evaluated at -4.7 eV and -5.1 eV respectively for 2,7 and 3,6 disubstituted carbazole derivatives. Incorporated as hole transporting materials in solid state DSSC, the 2,7 carbazole exhibits an efficiency conversion of 0.18 % while the 3,6 carbazole gives 0.34 % of efficiency conversion due to a better pore filling in the mesoporous TiO

Diphenylamino-substituted derivatives of 9-phenylcarbazole as glass-forming hole-transporting materials for solid state dye sensitized solar cells

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Star-shaped carbazole derivative based efficient solid-state dye sensitized solar cell

International audienceTwo new star-shaped carbazole molecules, including tri(9-(methoxyphenyl)carbazol-3-yl)amine named TMPCA having molecular glasses properties and hole transport properties were synthesized. Their thermal, optical, photophysical and electrochemical properties were studied. The carbazole based molecules exhibit high thermal stability with 5% weight loss temperatures over 480 °C with higher glass temperature transitions 164-175 °C than the classical spiro-OMeTAD reference molecule. Their optical band gaps (2.76 eV) are low enough not to hinder neither the absorption of the indoline sensitizer (D102) nor its photoexcitation and charge transfer. Solid state ionization potential (IPs) of TMPCA is well adapted to that of D102 and ensure a driving force ΔrG >0.2 eV for an efficient transfer and regeneration of the photo-oxidized dye. Solid-state dye sensitized solar cells ITO/TiO2/D102/T4MPCA/Au showed a power conversion efficiency of 2.23% with Jsc of 8.85 mA cm−2 under standard AM 1.5 simulated solar irradiation

Carbazole-based molecular glasses for efficient solid-state dye-sensitized solar cells

International audienceEfficient molecular glasses based on carbazole moiety used as hole transporting materials were synthesized. The role of the mono- or di-substitution of dimethoxy-diphenyl amine groups on the 3 and/or 6 position of the carbazole was evidenced. Their thermal, optical, photoelectrical, electrochemical properties as well as their photovoltaic characteristics on solid-state dye sensitized solar cells were investigated. The performance of these materials in solid-state DSSC based on TiO2 sensitized with the commercial indoline organic dye D102 is widely discussed. In such configuration, a power conversion efficiency of 3.4% and a fill factor of 0.53 are achieved with a 3,6-substitued carbazole molecular glass derivative, under standard AM 1.5 simulated solar irradiation. In addition, the Jsc value is even higher than the spiro-OMeTAD, due to its higher mobility. These results are found to be very promising since no specific optimization was performed on the devices yet. By comparison, the corresponding reference device incorporating spiro-OMeTAD as p-type organic semiconductor gives similar power conversion efficiency of 3.5%, showing the relevance of our approach

Pyrenyl-Functionalized Fluorene and Carbazole Derivatives as Blue Light Emitters

New pyrenyl mono- and disubstituted fluorene and carbazole derivatives were synthesized and investigated as blue-emitting materials. Most of the synthesized compounds were capable of forming glasses with glass transition temperatures up to 105 °C. The mono- and disubstituted compounds exhibited efficient emission in a diluted form with the peak wavelengths of 416 and 422 nm and quantum yields of 0.72 and 0.82, respectively. Photophysical properties of the compounds in dilute solutions and solid state were investigated experimentally and rationalized by density functional theory calculations. The calculations revealed a low energy barrier for intramolecular twisting in the ground and excited states. The electronic spectra of the compounds were dominated by an allowed “pyrene-like” S₀ → S₂ transition prevailing in nearly perpendicularly twisted molecular structures and competitive S₀ → S₁ transition becoming increasingly allowed for more planar conformers. The disubstituted compounds demonstrated a 3-fold enhanced oscillator strength of S₀ → S₁ transition, giving rise to the enhanced fluorescence quantum yield, significant shortening of the fluorescence lifetimes (from 2.5 ns down to 1.0 ns), and 3-fold reduced amplified spontaneous emission threshold as compared with those of the monosubstituted compounds. Introduction of the bulky dihexyl group into the pyrenyl-disubstituted fluorene enabled remarkable suppression of emission concentration quenching in a solid state and ensured high emission quantum yield (0.63) in the wet-casted neat films. Pyrenyl disubstitution of fluorene and a sterically hindered aliphatic group enabled observation of a low amplified spontaneous emission threshold (20 kW/cm²) for the compound dispersed in the inert polystyrene host at a rather large (5 wt %) chromophore concentration

Blue organic light-emitting diodes based on pyrazoline phenyl derivative

The results of an experimental study of the electroluminescent device made of ITO/CuI/2,6-di-tert.-butyl-4-(2,5-diphenyl-3,4-dihydro-2H-pyrazol-3-yl)- phenol (HPhP)/3,6-Di(9-carbazolyl)-9-(2-ethylhexyl) carbazole (TCz1)/Ca:Al with efficacy up to 10.63 cd/A are presented. HPhP provides blue emission with a peak wavelength at 445 nm. The layer of TCz1 acts as an electron-transporting layer. In the framework of density functional theory (DFT) approach the geometry configuration and energy levels of HPhP are found being in a good agreement with spectral and cyclic voltammogram data. © 2011 Elsevier B.V

Blue organic light-emitting diodes based on pyrazoline phenyl derivative

The results of an experimental study of the electroluminescent device made of ITO/CuI/2,6-di-tert.-butyl-4-(2,5-diphenyl-3,4-dihydro-2H-pyrazol-3-yl)-phenol (HPhP)/3,6-Di(9-carbazolyl)-9-(2-ethylhexyl) carbazole (TCz1)/Ca:Al with efficacy up to 10.63 cd/A are presented. HPhP provides blue emission with a peak wavelength at 445 nm. The layer of TCz1 acts as an electron-transporting layer. In the framework of density functional theory (DFT) approach the geometry configuration and energy levels of HPhP are found being in a good agreement with spectral and cyclic voltammogram data