Graduate Institute of Photonics and Optoelectronics

Taipei, Taiwan

Graduate Institute of Photonics and Optoelectronics

Taipei, Taiwan

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Chang H.,National Taiwan University | Yang Y.-J.,National Taiwan University | Li H.-C.,National Taiwan University | Hsu C.-C.,National Taiwan University | And 2 more authors.
Journal of Power Sources | Year: 2013

We investigate the nanoporous TiO2 films sintered by atmospheric pressure plasma jets (APPJs) and their applications as photoanodes of dye-sensitized solar cells (DSSCs). A 30-s APPJ-sintered nanoporous TiO 2 layer exhibits an additional absorption band between 400 and 500 nm in wavelength, attributed to incomplete removal of the organic solvents in the pastes. For TiO2 layers sintered by APPJs for 60 s and beyond, the absorption spectra are nearly identical to those of a conventional 15 min, 510 °C calcined sample. The XRD and XPS results indicate similar characteristics for APPJ-sintered and furnace-sintered TiO2 films. A DSSC with a 30-s APPJ-sintered TiO2 photoanode shows poor cell efficiency with an extremely large TiO2/dye/electrolyte electron transport interfacial resistance and a short carrier lifetime. As the APPJ treatment time reaches 60 s and beyond, the power conversion efficiencies become comparable to that of a sample with a 510 °C conventionally calcined TiO2 photoanode. Our experimental results verify that a 60-s APPJ sintering process is sufficient to replace a conventional 15 min, 510 °C furnace calcination process for TiO2 photoanodes of DSSCs. The ultra-short sintering process is made possible by the synergistic effect of the temperature and the reactivity of the APPJ, which can lower the fabrication cost. © 2013 Elsevier B.V. All rights reserved.


Mao M.-H.,No. 1 | Mao M.-H.,Graduate Institute of Photonics and Optoelectronics | Mao M.-H.,National Taiwan University | Chien H.-C.,No. 1 | And 5 more authors.
Optics Express | Year: 2011

We fabricated current-injection InGaAs quantum-dot microdisk lasers with benzocyclobutene cladding in this work. The microdisk pedestal diameter is carefully designed to facilitate carrier injection and modal control. With this structure, low threshold current of 0.45 mA is achieved at room temperature from a device of 6.5 μm in diameter with single-mode emission from quantum-dot ground states. The negative characteristic temperature T0 of threshold current is observed between 80 K and 150 K. The transition temperature from negative T0 to positive T0 is 150 K which is higher than that of the edge-emitting lasers fabricated from the same wafer. This phenomenon indicates the lower loss level of our microdisk cavities. These microdisk lasers also show positive T0 significantly higher than that of the edge-emitting lasers from the same wafer. © 2011 Optical Society of America.


Chen L.-Y.,Graduate Institute of Photonics and Optoelectronics | Huang H.-H.,Graduate Institute of Photonics and Optoelectronics | Chang C.-H.,Graduate Institute of Photonics and Optoelectronics | Huang Y.-Y.,Graduate Institute of Photonics and Optoelectronics | And 4 more authors.
Optics Express | Year: 2011

Strain in the semiconductor light emitting layers has profound effect on the energy band structure and the optical properties of the light emitting diodes (LEDs). Here, we report the fabrication and characterization of GaN nanorod LED arrays. We found that the choice of nanorod passivation materials results in the variation of strain in the InGaN/GaN quantum wells, and thus the corresponding change of light emission properties. The results were further investigated by performing Raman measurement to understand the strain of nanorods with different passivation materials and by calculating the optical transition energy of the devices under the influence of strain-induced deformation potential and the piezoelectric polarization field. © 2011 Optical Society of America.


Ho Y.-H.,Academia Sinica, Taiwan | Ho Y.-H.,National Taiwan University | Chen K.-Y.,Graduate Institute of Photonics and Optoelectronics | Peng K.-Y.,Academia Sinica, Taiwan | And 6 more authors.
Optics Express | Year: 2013

A precisely controlled metallic nanomesh was fabricated by using nanosphere lithography to pattern the silver thin film to form hexagonal nanohole arrays with excellent uniformity, high conductivity and good transparency. An Alq3 based OLED, with the silver nanomesh electrode of high fill factor of 70.2% demonstrated a considerable luminous efficiency of 4.8 cd/A, which is 60.9% higher than the referenced device with ITO anode. The periodical nanohole array not only increased the transparency but also helped extracting surface plasmonic wave in organic layers. By attaching the microlens array to further extract the trapped light in substrate, the extraction efficiency enhancement of device with nanomesh anode was 73.8% higher than 50.2% of the referenced device with ITO anode. And the overall current efficiency of device with nanomesh anode was 87.7% higher than traditional ITO based device. © 2013 Optical Society of America.


Chou C.-T.,National Taiwan University of Science and Technology | Lin C.-H.,Graduate Institute of Photonics and Optoelectronics | Tai Y.,National Taiwan University of Science and Technology | Liu C.-H.J.,National Taiwan University of Science and Technology | And 3 more authors.
Journal of Physical Chemistry Letters | Year: 2012

In this Letter, we investigated the effect of the molecular stacking orientation on the open circuit voltage (V OC) of pentacene-based organic solar cells. Two functionalized pentacenes, namely, 6,13-diphenyl- pentacene (DP-penta) and 6,13-dibiphenyl-4-yl-pentacene (DB-penta), were utilized. Different molecular stacking orientations of the pentacene derivatives from the pristine pentacene were identified by angle-dependent near-edge X-ray absorption fine structure measurements. It is concluded that pentacene molecules stand up on the substrate surface, while both functionalized pentacenes lie down. A significant increase of the V OC from 0.28 to 0.83 V can be achieved upon the utilization of functionalized pentacene, owing to the modulation of molecular stacking orientation, which induced a vacuum-level shift. © 2012 American Chemical Society.


Chou S.-H.,National Taiwan University | Tsai C.-H.,Graduate Institute of Photonics and Optoelectronics | Tsai C.-H.,National Taiwan University | Tsai C.-H.,National Dong Hwa University | And 4 more authors.
Chemistry - A European Journal | Year: 2014

Two D-π-A′-A regioisomers (A-IDT-D and D-IDT-A) featuring 4,4′-di-p-tolyl-4 H-indeno[1,2-b]-thiophene as a π linker (π) between the diarylamino donor (D) and the pyrimidine-cyanoacrylic acid acceptor (A′-A) have been successfully synthesized and characterized as efficient sensitizers for the dye-sensitized solar cells (DSSCs). The different arrangements of the D and A′-A blocks on the unsymmetrical indenothiophene (IDT) core render the dipole of IDT being along (A-IDT-D) or opposite (D-IDT-A) to the direction of intramolecular (donor-to-acceptor) charge transfer, and thus induce variations in the physical properties. The experimental observations correlated well with the theoretical analyses, clearly revealing the trade-off between the molar extinction coefficient (ε) and the S0→S1 transition energy. As a result, a superior ε value was observed for D-IDT-A, whereas a bathochromic shift in the absorption occurred in A-IDT-D. The larger ε value of D-IDT-A together with its more favorable energy level relative to TiO2 led to a higher power conversion efficiency of 7.41 % for the D-IDT-A-based DSSC, retaining approximately 95 % of the N719-based DSSC efficiency. This work manifests the clear structure-property relationship for the case of donor and acceptor components being connected by an unsymmetrical π linker and provides insights for molecular engineering of organic sensitizers. © 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.


Liu S.-W.,Academia Sinica, Taiwan | Lee C.-C.,National Taiwan University of Science and Technology | Lin C.-F.,Graduate Institute of Photonics and Optoelectronics | Huang J.-C.,National Taiwan University of Science and Technology | And 2 more authors.
Journal of Materials Chemistry | Year: 2010

A stable exciton-blocking layer (EBL) with rigid ball-like 4-hydroxy-8-methyl-1,5-naphthyridine aluminium chelate (AlmND3) has been newly developed for organic photovoltaics (OPVs) based on a double-heterostructure of pentacene/C60/EBL. Unlike the common EBL materials, such as tris-(8-hydroxyquinoline)aluminium (Alq3) and bathocuproine (BCP), AlmND3 exhibits a relatively high electron mobility (∼10-4 cm2 V-1 s-1 at the electric field of 6.4 × 105 V cm-1) and a wide band gap energy (∼3.3 eV) in addition to a high glass transition temperature (Tg ∼ 194 °C). Having such EBL between active region (pentacene/C60) and the metal cathode, pristine device performances were comparable with those of BCP-based OPV due to its high mobility and wide band gap energy. Moreover, due to its significantly higher Tg than that of BCP, an extended lifetime performance was observed for AlmND 3-based OPV, compared with the BCP-based OPV aged at the elevated temperature of 75 °C. © 2010 The Royal Society of Chemistry.


Chang C.-H.,Graduate Institute of Photonics and Optoelectronics | Chen C.-C.,Graduate Institute of Photonics and Optoelectronics | Wu C.-C.,Graduate Institute of Photonics and Optoelectronics | Chang S.-Y.,National Tsing Hua University | And 2 more authors.
Organic Electronics: physics, materials, applications | Year: 2010

We report successful fabrication of high-color-rendering pure-white phosphorescent organic light-emitting devices (OLEDs) by employing a true-blue iridium complex Ir(dfbppy)(fbppz)2 and a wide-bandwidth yellow emitting osmium complex Os(bptz)2(dppee). The two-component phosphorescent white OLED exhibited a high color rendering index (CRI) of 81 and CIEx,y coordinates close to the ideal white emission (0.33, 0.33). By doping the yellow phosphors into the hole-transport layer and the electron-transport layer adjacent to the blue-emitting layer and thereby forming a triple-emitting-layer device structure, we obtained WOLED which exhibited rather stable colors at different biases/brightnesses. Such high-CRI pure-white two-component WOLEDs yielded EL efficiencies of up to 9.5%, 22.9 cd/A, and 20 lm/W for the forward directions. © 2009 Elsevier B.V. All rights reserved.


Chang C.-H.,Graduate Institute of Photonics and Optoelectronics | Cheng H.-C.,Graduate Institute of Photonics and Optoelectronics | Lu Y.-J.,Graduate Institute of Photonics and Optoelectronics | Tien K.-C.,Graduate Institute of Photonics and Optoelectronics | And 4 more authors.
Organic Electronics: physics, materials, applications | Year: 2010

The combination of white organic light-emitting devices (OLED) and color filters is one of the most promising technologies for full-color OLED displays. Yet, the transmission spectra of most available color filters are broad and poorly match the electroluminescence spectra of white OLEDs, yielding less saturated filtered colors and small color gamut for displays. In this work, we report that by employing the microcavity structure only in green pixels for such OLED display technology, one can simultaneously achieve simplification the manufacturing process, enhancement of color performances, and enhancement in efficiencies for OLED displays. © 2009 Elsevier B.V. All rights reserved.


Chang C.-H.,Graduate Institute of Photonics and Optoelectronics | Tien K.-C.,Graduate Institute of Photonics and Optoelectronics | Chen C.-C.,Graduate Institute of Photonics and Optoelectronics | Lin M.-S.,Graduate Institute of Photonics and Optoelectronics | And 6 more authors.
Organic Electronics: physics, materials, applications | Year: 2010

By utilizing a newly developed deep-blue iridium complex along with efficient green and orange-red phosphors, we have successfully demonstrated efficient three-component phosphorescent white-emitting organic light-emitting devices (WOLEDs) with excellent performances. Such WOLEDs were based on the deep-blue phosphorescent OLEDs architecture with double emitting layers and double confining layers; portions of the deep-blue phosphors were selectively replaced with green and orange-red phosphors, thereby forming a structure with the green/orange-red emitting layers sandwiched between the two deep-blue emitting layers. Such three-component phosphorescent WOLEDs yielded a high color rendering index (CRI) of up to 94 and Commission Internationale de l'Eclairage (CIE) coordinates close to the ideal equal-energy white (0.33, 0.33). Furthermore, they exhibited rather stable colors and high CRI over a wide brightness range of 102-104 cd/m2 and yielded electroluminescence efficiencies of up to 10.3%, 24.0 cd/A and 16.4 lm/W for the forward directions. © 2009 Elsevier B.V. All rights reserved.

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