Shu-Hua Chou

A Low-Energy-Gap Organic Dye for High-Performance Small-Molecule Organic Solar Cells

A novel donor-acceptor-acceptor (D-A-A) donor molecule, DTDCTB, in which an electron-donating ditolylaminothienyl moiety and an electron-withdrawing dicyanovinylene moiety are bridged by another electron-accepting 2,1,3-benzothiadiazole block, has been synthesized and characterized. A vacuum-deposited organic solar cell employing DTDCTB combined with the electron acceptor C(70) achieved a record-high power conversion efficiency (PCE) of 5.81%. The respectable PCE is attributed to the solar spectral response extending to the near-IR region and the ultracompact absorption dipole stacking of the DTDCTB thin film.

Organic dyes containing coplanar diphenyl-substituted dithienosilole core for efficient dye-sensitized solar cells.

Two new organic dyes adopting coplanar diphenyl-substituted dithienosilole as the central linkage have been synthesized, characterized, and used as the sensitizers for dye-sensitized solar cells (DSSCs). The best DSSC exhibited a high power conversion efficiency up to 7.6% (TP6CADTS) under AM 1.5G irradiation, reaching approximately 96% of the ruthenium dye N719-based reference cell under the same conditions.

A new benzimidazole/carbazole hybrid bipolar material for highly efficient deep-blue electrofluorescence, yellow–green electrophosphorescence, and two-color-based white OLEDs

The bipolar molecule CPhBzIm exhibits an excellent solid state photoluminescence quantum yield (ΦPL = 69%), triplet energy (ET = 2.48 eV), and bipolar charge transport ability (μh ≈ μe ≈ 10−6–10−5 cm2 V−1 s−1). We have used it to fabricate a non-doped deep-blue organic light emitting diode (OLED) exhibiting promising performance [ηext = 3%; CIE = (0.16, 0.05)] and to serve as host material for a yellow–green phosphorescent OLED [ηext = 19.2%; CIE = (0.42, 0.56)]. Exploiting these dual roles, we used CPhBzIm in a simple singly doped, two-color-based white OLED (ηext = 7%; CIE = 0.31, 0.33).

Efficient organic DSSC sensitizers bearing an electron-deficient pyrimidine as an effective π-spacer

A series of new push–pull organic dyes incorporating electron-deficient pyrimidine as the π-spacer have been synthesized, characterized, and used as the sensitizers for dye-sensitized solar cells (DSSCs). In comparison with the model compound M-TP, which adopts phenylene as the π-spacer, the tailor-made dyes display enhanced spectral responses in the red portion of the solar spectrum. Through the introduction of two hexyloxy chains on the diphenylthienylamine donor, the DSSC employing dye OHexDPTP exhibited high power conversion efficiency up to 7.64% under AM1.5G irradiation.

A diarylborane-substituted carbazole as a universal bipolar host material for highly efficient electrophosphorescence devices

Recently bipolar phosphorescent host materials have attracted wide attention since they can achieve better charge balance and hence better device performance. In this work, we report the synthesis and physical properties of a novel bipolar host material containing the dimesityl borane/carbazole hybrid, CMesB. With a high triplet energy, CMesB is considered a promising universal host material and has been applied to phosphorescent OLEDs of various colors. Red/green/blue/white (RGBW) OLEDs based on CMesB all show high external quantum efficiencies (20.7% for red, 20.0% for green, 16.5% for blue, and 15.7% for white) at practical brightnesses. The results indicate that the bipolar host CMesB with high triplet energy has high potential in manufacturing RGBW OLEDs for display or lighting applications.

Incorporation of a CN group into mCP: a new bipolar host material for highly efficient blue and white electrophosphorescent devices

A novel bipolar host material mCPCN has been designed and synthesized by incorporating the electron-accepting CN group into the well-known benchmark host material mCP. Compared to mCP, the incorporation of the simple and small CN group significantly improves thermal/morphological stabilities (Tg = 97 °C and Td = 313 °C) and increases the electron affinity, while keeping electronic transition energies unaltered and maintaining a high triplet energy (ET = 3.03 eV). Characteristics of single-carrier devices containing mCPCN indicate its rather balanced hole/electron injection and transport properties. Highly efficient blue phosphorescent organic light emitting devices (PhOLEDs) with maximum external quantum, current and power efficiencies of 26.4%, 58.6 cd A−1, and 57.6 lm W−1, respectively, were achieved using mCPCN as the bipolar host material and bis[(4′,6′-difluorophenyl)pyridinato-N,C2′]iridium(III) picolinate (FIrpic; ET = 2.65 eV) as the triplet emitter. Furthermore, blue PhOLEDs adopting mCPCN exhibit impressively low efficiency roll-offs, retaining high quantum efficiencies of ∼25% at 1000 cd m−2 and ∼20% even at 8000 cd m−2. mCPCN has also been successfully used in implementing highly efficient white PhOLEDs having external quantum efficiencies in excess of 23%.

Indolo[3,2-b]carbazole/benzimidazole hybrid bipolar host materials for highly efficient red, yellow, and green phosphorescent organic light emitting diodes

By incorporating electron-accepting benzimidazole and electron-donating indolo[3,2-b]carbazole into one molecule, two novel donor–acceptor bipolar host materials, TICCBI and TICNBI, have been synthesized. The photophysical and electrochemical properties of the hybrids can be tuned through the different linkages (C- or N-connectivity) between the electronic donor and acceptor components. The promising physical properties of these two new compounds made them suitable for use as hosts doped with various Ir or Os-based phosphors for realizing highly efficient phosphorescent organic light emitting diodes (PhOLEDs). PhOLEDs using TICCBI and TICNBI as hosts incorporated with Ir-based emitters such as green (PPy)2Ir(acac), yellow (Bt)2Ir(acac), and two new red emitters (35dmPh-6Fiq)2Ir(acac) (i3) and (4tBuPh-6Fiq)2Ir(acac) (i6) accomplished high external quantum efficiencies ranging from 14 to 16.2%. Nevertheless, the red PhOLED device incorporating TICNBI doped with the red emitter osmium(II) bis[3-(trifluoromethyl)-5-(4-tert-butylpyridyl)-1,2,4-triazolate]dimethylphenylphosphine [Os(bpftz)2(PPhMe2)2] achieved a maximum external quantum efficiency, current efficiency, and power efficiency of 22%, 28 cd A−1, and 22.1 lm W−1, respectively, with CIE coordinates of (0.65,0.35). The external quantum efficiency remained high (20%) as the brightness reached to 1000 cd m−2, suggesting balanced charge fluxes within the emitting layer, rendering devices with limited efficiency roll-off.

Electrochemistry and electrogenerated chemiluminescence of a spirobifluorene-based donor (triphenylamine)-acceptor (2,1,3-benzothiadiazole) molecule and its organic nanoparticles.

A new D-A-π-A-D molecule (Spiro-BTA) containing two 2,1,3-benzothiadiazole (BTA) as the acceptor (A) and triphenylamine as the donor (D) bridged by a spirobifluorene moiety has been synthesized. The novel D-A molecule shows intense red emission (612 nm) with a high PL quantum yield (Φ(PL) = 0.51) in a solid film. A cyclic voltammogram of Spiro-BTA in 1:2 MeCN:benzene/0.1 M Bu(4)NPF(6) shows two reversible oxidation waves and one reversible reduction wave. The first oxidation wave and reduction wave were assigned as two successive electron transfer peaks separated by ∼50 mV related to the oxidation of the two noninteracting donors and the reduction of the two noninteracting acceptors, respectively. Electrogenerated chemiluminescence (ECL) of Spiro-BTA upon cyclic oxidation and reduction in MeCN:benzene 1:2 shows a very bright and stable red emission that could be seen in a well-lit room. Using a reprecipitation method, well-dispersed organic nanoparticles (NPs) of the Spiro-BTA were prepared in aqueous solution. The nanoparticles were analyzed by dynamic light scattering (DLS) and scanning electron microscopy (SEM), yielding a NP size (without surfactant) of 130 ± 20 nm, while with surfactant, 100 ± 20 nm. Bathochromic shifts of absorption spectra (∼16 ± 2 nm), as compared to that of the dissolved Spiro-BTA in THF, were observed for both NPs in water and as a thin film. While blue shifts (14 ± 2 nm) were observed for the photoluminescence (PL). The PL intensity of the Spiro-BTA nanoparticles was slightly enhanced (Φ(PL) of nanoparticles in water = 48%) over that of the dissolved Spiro-BTA in THF. The ECL of the organic Spiro-BTA nanoparticles in aqueous solution could be observed upon oxidation with tri-n-propylamine as a coreactant.

A Novel Amine-Free Dianchoring Organic Dye for Efficient Dye-Sensitized Solar Cells

An amine-free oligothiophene-based dye (BTB) featuring a tailor-made dianchoring function, a spiro-configured central unit, and bulky end-capping TIPS groups to diminish intermolecular interactions and to suppress aggregation-induced self-quenching was synthesized to achieve efficient dye-sensitized solar cells with a high power conversion efficiency of 6.52%.

Indolo[2,3-b]carbazole Synthesized from a Double-Intramolecular Buchwald–Hartwig Reaction: Its Application for a Dianchor DSSC Organic Dye

A new synthetic strategy for indolo[2,3-b]carbazole via a double-intramolecular Buchwald-Hartwig reaction has been established. The N-alkylated indolo[2,3-b]carbazole then was adopted as the geometry-fixed core for the synthesis of a new molecule (ICZDTA) bearing two bithiophene π-bridged 2-cyanoacrylic acid groups as the bidentate anchor. The bidentate anchoring together with efficient HOMO (indolo[2,3-b]carbazole) → LUMO (TiO2 nanocluster) electron transfer leads to the successful development of ICZDTA-based DSSC with a power conversion efficiency of 6.02%.