7 research outputs found
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
Three-terminal light-emitting device with adjustable emission color
A three-terminal organic light-emitting device with a periodic interrupted middle electrode is developed to allow for an adjustable emission color. The emission results from three independent light-emitting diodes with one diode utilizing exciplex emission. An equivalent electrical circuit is suggested taking the current–voltage characteristics and the direction of current flow through the organic structure into account. Two diodes are formed between the embedded middle electrode and the LiF/Al top and ITO bottom electrode, respectively, and the third diode utilizes that part of the device without the middle-electrode exhibiting exciplex emission. It will be shown that the spectrum of the emitted light can be tuned from blue to orange by controlling the applied potentials to the device terminals
Star-Shaped Carbazole Derivatives for Bilayer White Organic Light-Emitting Diodes Combining Emission from Both Excitons and Exciplexes
Star-shaped carbazole-based compounds were synthesized
by the Buchwald–Hartvig
method. The materials were examined by various experimental and theoretical
methods, including differential scanning calorimetry, UV spectrometry,
electron photoemission, time-of-flight techniques, and DFT (B3LYP)
calculations. The synthesized compounds showed high thermal stability
with the initial weight loss temperature higher than 400 °C.
The electron photoemission spectra of the layers of the amorphous
materials showed ionization potentials of 4.9 eV. TriÂ(9-hexylcarbazol-3-yl)Âamine
showed high hole mobility (μ = 10<sup>–3</sup> cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup> at an electric
field of 3.6 × 10<sup>5</sup> V/cm). The star-shaped compounds
were used for the preparation of bilayer white organic light-emitting
diodes which combine emission from both excitons and exciplexes. The
brightness of the white organic light emitting diode at 7 V is 300
cd/m<sup>2</sup> with current efficiency 2.3 cd/A and CIE coordinates
(0.37, 0.35) which are very close to the equienergy white point (0.33,
0.33)
Structure Properties Relationship of Donor–Acceptor Derivatives of Triphenylamine and 1,8-Naphthalimide
Solution-processable donor–acceptor molecules
consisting
of triphenylamine core and 1,8-naphthalimide arms were designed and
synthesized by palladium-catalyzed Heck reaction. Dilute solutions
of the synthesized compounds show strong absorption peaks in the visible
wavelength range from 400 to 550 nm, which can be ascribed to the
intramolecular charge transfer. Fluorescence quantum yields of dilute
solutions of the synthesized materials range from 0.45 to 0.70, while
those of the solid samples are in the range of 0.09–0.18. The
synthesized molecules exhibit high thermal stability with the thermal
degradation onset temperatures ranging from 431 to 448 °C. The
compounds form glasses with glass-transition temperatures of 55–107
°C. DFT calculations show that HOMO and LUMO orbitals are almost
entirely localized on the donor and acceptor moieties, respectively.
Consequently, the frontier orbital energies for the three synthesized
compounds are similar and practically do not depend on the number
of 1,8-naphthalimide moieties. Ionization potentials of the solid
samples (5.75–5.80 eV) are comparable. The charge-transporting
properties of the synthesized materials were studied using xerographic
time-of-flight method. Hole mobilities in the layers of the compounds
having one and two 1,8-naphthalimide moieties exceed 10<sup>–3</sup> cm<sup>2</sup>·V<sup>–1</sup>·s<sup>–1</sup> at high electric fields at room temperature. The differences on
the hole mobilities between the three synthesized compounds are discussed
in the frame of Marcus theory by comparing the reorganization energy
and electronic coupling parameters