Vinich Promarak

Tri‐Diketopyrrolopyrrole Molecular Donor Materials for High‐Performance Solution‐Processed Bulk Heterojunction Solar Cells

Two new high-performance DPP-containing donor molecules employing a molecular architecture with three DPP chromorphores (tri-DPP) in conjugated backbones are synthesized and characterized. The two tri-DPP molecules with only a structural difference on alkyl substitutions, when blended with PC71 BM, lead to power conversion efficiencies up to 4.8 and 5.5%, respectively.

Bifunctional anthracene derivatives as non-doped blue emitters and hole-transporters for electroluminescent devices

New highly fluorescent bifunctional anthracenes showed high thermal and electrochemical stability, and great potential as both blue emitters and hole-transporters for OLEDs. Deep-blue and Alq3-based green devices with maximum efficiencies and CIE coordinates of 1.65 and 6.25 cd A(-1), and (0.15, 0.16) and (0.26, 0.49) were achieved, respectively.

Blue light-emitting and hole-transporting materials based on 9,9-bis(4-diphenylaminophenyl)fluorenes for efficient electroluminescent devices

New bifunctional materials namely BTTF, TPTF and BPTF having 9,9-bis(4-diphenylaminophenyl)fluorene as a molecular platform were synthesized and characterized. These molecules showed strong blue emission in both solution and solid state with a solution fluorescence quantum efficiency of up to 74% and were thermally stable amorphous materials with glass transition temperature well above 170 °C. The abilities of these materials as blue light-emitting materials for blue OLEDs and hole-transporting materials for green OLEDs in terms of device performance and thermal property were superior to a commonly used N,N′-diphenyl-N,N′-bis(1-naphthyl)-(1,1′-biphenyl)-4,4′-diamine (NPB). Efficient non-doped blue and Alq3-based green OLEDs with maximum luminance efficiencies and CIE coordinates of 2.06 cd A−1 and (0.15, 0.13), and 4.94 cd A−1 and (0.29, 0.52) were achieved, respectively, with BPTF having two pyrene substituents as the emitting layer and the hole-transporting layer, respectively.

Effects of Stereoisomerism on the Crystallization Behavior and Optoelectrical Properties of Conjugated Molecules

Three stereoisomers of DPP(TBFu)2 are separated and identified to investigate the effects of stereoisomerism on crystal structures and the optoelectrical properties. The crystal structures and FET mobility are sensitive to stereoisomers, in which the mesomer possesses the highest carrier mobility and the greatest crystallization tendency to dominate the crystallization in spin-cast films of the as-synthesized stereoisomeric mixture.

Pyrene-functionalized carbazole derivatives as non-doped blue emitters for highly efficient blue organic light-emitting diodes

A series of pyrene-functionalized carbazole derivatives, namely N-dodecyl-3,6-di(pyren-1-yl)carbazole (CP2), N-dodecyl-1,3,6-tri(pyren-1-yl)carbazole (CP3) and N-dodecyl-1,3,6,8-tetra(pyren-1-yl)carbazole (CP4), are synthesized and characterized as simple non-doped solution processed blue emitters for OLEDs. By multiple substitution of pyrene on the carbazole ring, we are able to retain the high blue emissive ability of pyrene in the solid as well as improve the amorphous stability and solubility of the material. These materials show high solution fluorescence quantum efficiencies (up to 94%) and can form morphologically stable amorphous thin films with Tg as high as 170 °C. Solution processed double-layer OLEDs using these materials as non-doped blue emitters exhibit good device performance with luminance efficiencies up to 2.53 cd A−1. Their multi-layer devices exhibit outstanding performances. The CP2-based device shows a low turn-on voltage (down to 2.6 V) with an excellent blue emission color (λem = 436 nm) and CIE coordinates of (0.16, 0.14), while the CP3 and CP4-based blue devices also display low turn-on voltages (down to 2.7 V) with high luminance (up to 24479 cd m−2) and luminance efficiencies (up to 6.92 cd A−1).

Carbazole-dendrimer-based donor-π-acceptor type organic dyes for dye-sensitized solar cells: effect of the size of the carbazole dendritic donor.

A series of novel D-π-A type organic dyes, namely, GnTA (n = 1-4), containing carbazole dendrons up to fourth generation as a donor, bithiophene as π-linkage, and cyanoacrylic acid as acceptor were synthesized and characterized for applications in dye-sensitized solar cells (DSSCs). The photophysical, thermal, electrochemical, and photovoltaic properties of the new dyes as dye sensitizers were investigated, and the effects of the carbazole dendritic donors on these properties were evaluated. Results demonstrated that increasing the size or generation of the carbazole dendritic donor of the dye molecules enhances their total light absorption abilities and unluckily reduces the amount of dye uptake per unit TiO2 area because of their high molecular volumes. The latter was found to have a strong effect on the power conversion efficiency of DSSCs. Importantly, electrochemical impedance spectroscopy (EIS) revealed that the size or generation of the donor had a significant influence on a charge-transfer resistance for electron recombination at the TiO2/electrolyte interface, causing a difference in open circuit voltage (Voc) of the solar cells. Among them, dye G1TA containing first generation dendron as a donor (having lowest molecular volume) exhibited the highest power conversion efficiency of 5.16% (Jsc = 9.89 mA cm(-2), Voc = 0.72 V, ff = 0.73) under simulated AM 1.5 irradiation (100 mW cm(-2)).

Novel Bis[5-(fluoren-2-yl)thiophen-2-yl]benzothiadiazole End-Capped with Carbazole Dendrons as Highly Efficient Solution-Processed Nondoped Red Emitters for Organic Light-Emitting Diodes

A series of novel red-emitting bis[5-(fluoren-2-yl)thiophen-2-yl]benzothiadiazole-cored dendrimers containing carbazole dendrons up to the third generation are synthesized. Their photophysical, thermal, electrochemical, and electroluminescent properties as nondoped solution-processed red light-emitters for OLEDs are investigated. By using carbazole dendrons as the end caps, we are able to reduce the crystallization and retain the high emissive ability of a planar fluorescent core in the solid state as well as improve the thermal stability of the material. These dendrimers show a bright-red fluorescence and can form morphologically stable amorphous thin films with glass-transition temperatures as high as 283 °C. Simple structured solution-processed OLEDs using these materials as hole-transporting nondoped emitters and BCP as the hole-blocking layer emit a stable red color around 622-645 nm, with high luminance efficiencies (up to 4.80 cd A(-1) at 1.2 mA cm(-2)) and CIE coordinates of (0.65, 0.33), which are close to the pure red color.

Theoretical investigation of novel carbazole-fluorene based D-π-A conjugated organic dyes as dye-sensitizer in dye-sensitized solar cells (DSCs).

The ground state structure and frontier molecular orbital of newly synthesized carbazole‐fluorene based D‐π‐A organic dyes, CFP1A, CFP2A, CFP1CA, and CFP2CA, were theoretically investigated using density functional theory (DFT) at B3LYP/6‐31G(d,p) level. These dye molecules have been constructed based on carbazole‐fluorene as the electron‐donating moiety while introducing benzene units as π‐spacer connected to different anchor groups, such as acrylic acid and cyanoacrylic acid, as acceptors. The electronic vertical excitation energies and absorption wavelength were carried out using time‐dependent DFT (TD‐DFT). Furthermore, the adsorptions of phenylacrylic acid and phenylcyanoacrylic acid on the TiO2 anatase (101) surface were carried out by means of quantum‐chemical periodic calculations employing periodic PBE functional with DNP basis set. The results promise that anchor dyes with strong withdrawing CN group have easier injected electron to the conduction band of semiconductor implying that CFP1CA and CFP2CA show better performance among four dyes. Additionally, the intramolecular charge transfers (ICT) from electron donor group to anchoring group of CFP1CA and CFP2CA have shown better performance. The calculated results provide the efficiency trend of our new dyes as CFP1CA ≈ CFP2CA > CFP1A ≈ CFP2A which are excellently agree with experimental observation.

Bis(carbazol-9-ylphenyl)aniline end-capped oligoarylenes as solution-processed nondoped emitters for full-emission color tuning organic light-emitting diodes.

A series of bis(3,6-di-tert-butylcarbazol-9-ylphenyl)aniline end-capped oligoarylenes, BCPA-Ars, are synthesized by double palladium-catalyzed cross-coupling reactions. By using this bis(carbazol-9-yl)triphenylamine moiety as an end-cap, we are able to reduce the crystallization and retain the high-emission ability of these planar fluorescent oligoarylene cores in the solid state, as well as improve the amorphous stability and solubility of the materials. The results of optical and electrochemical studies show that their HOMOs, LUMOs, and energy gaps can be easily modified or fine-tuned by either varying the degree of π-conjugation or using electron affinities of the aryl cores which include fluorene, oligothiophenes, 2,1,3-benzothiadiazole, 4,7-diphenyl-4-yl-2,1,3-benzothiadiazole, and 4,7-dithien-2-yl-2,1,3-benzothiadiazole. As a result, their emission spectra measured in solution and thin films can cover the full UV-vis spectrum (426-644 nm). Remarkably, solution-processed nondoped BCPA-Ars-based OLEDs could show moderate to excellent device performance with emission colors spanning the whole visible spectrum (deep blue to red). Particularly, the RGB (red, green, blue) OLEDs exhibit good color purity close to the pure RGB colors. This report offers a practical approach for both decorating the highly efficient but planar fluorophores and tuning their emission colors to be suitable for applications in nondoped and solution-processable full-color emission OLEDs.

Economical and green biodiesel production process using river snail shells-derived heterogeneous catalyst and co-solvent method.

River snail shells-derived CaO was used as a heterogeneous catalyst to synthesize biodiesel via transesterification of palm oil with methanol. The shell materials were calcined in air at 600-1000°C for 3h. Physicochemical properties of the resulting catalysts were characterized by TGA-DTG, XRD, SEM, BET, XRF, FT-IR and TPD. CaO catalyzed transesterification mechanism of palm oil into biodiesel was verified. The effects of adding a co-solvent on kinetic of the reaction and %FAME yield were investigated. %FAME yield of 98.5%±1.5 was achieved under the optimal conditions of catalyst/oil ratio of 5wt.%; methanol/oil molar ratio of 12:1; reaction temperature of 65°C; 10%v/v of THF in methanol and reaction time of 90min. The results ascertained that river snail shells is a novel raw material for preparation of CaO catalyst and the co-solvent method successfully decreases the reaction time and biodiesel production cost.