Browsing by Author "Wang, Po-Hsun"

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Adjusting optical resonance thickness to increase the conversion efficiency of polymer solar cells
(2010-05-01)
Tsai, Yu Sheng
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Lin, Jian-Shian
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Chu, Wei-Ping
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Wang, Po-Hsun
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Juang, Fuh-Shyang
The derivatives of C(60), [6,6]-phenyl C61-butyric acid methyl ester (PCBM), and 3-hexylthiophene (P3HT) were dissolved in DCB solvent, then spin coated into an active layer for polymer solar cells. The experimental parameters were studied carefully to obtain the optimum power conversion efficiency (PCE). The primary process for generation of photocurrent in an organic photovoltaic device is the generation of bound electron-hole pairs (excitons) by absorption of energy (photons) from the optical electric field. Modeling was based on the assumption that the photocurrent generation process is the result of the creation and diffusion of photogenerated species (excitons), which are dissociated by charge transfer at the active layer. Improve organic optics absorb by insert organic layer (CuPc or C60) at the active layer/Al interface. This research is divided into two components. First part, we use n-type C60 as transmission layer. When an optimum thickness of C(60) is 5 nm, the J(sc) of polymer solar cell can be increased from 7.26 mA/cm(2) to 7.7 mA/cm(2). The V(oc) decrease is because the energy level of C60 LUMO (lowest unoccupied molecular orbital) at 4.5 eV is higher than the 3.7 eV of PCBM. Second part, we use p-type CuPc as transmission layer. When an optimum thickness of CuPc is 3 nm, the short circuit photo-current density (J(sc)) and open circuit voltage (Voc) of polymer solar cell can be increased from 7.26 mA/cm2 to 8.0 mA/cm2 and 0.56-0.58 V, respectively. The reason is the same as C(60). The Voc increase is because the energy level of CuPc LUMO (lowest unoccupied molecular orbital) at 3.1 eV is lower than the 3.7 eV of PCBM. The Jsc increase is because the 3 nm of CuPc leads to a constructive interference happened in the active layer and thus optical absorption increases. In this study we used 3 nm of CuPc at the active layer/Al interface to enhance the short circuit current density, and the efficiency was increased to 2.94%. (C) 2010 Elsevier B. V. All rights reserved.
Angular color variation in micron-scale light-emitting diode arrays
(2019-08-05)
Yang, Shu-Mei
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Wang, Po-Hsun
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Chao, Chia-Hsin
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Chu, Chun-Wen
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Yeh, Yin-Tien
A simulation scheme was developed to explore the light distribution of full-color micron-scale light-emitting diode (LED) arrays. The influences of substrate thickness, patterning, and cutting angle of the substrate on several important features, such as light field pattern, light extraction efficiency, and color variation, were evaluated numerically. An experiment was conducted; the results were consistent with simulation results for a 225 x 125 mu m(2) miniLED and those for an 80 x 80 mu m(2) microLED. Based on the simulation results, the light extraction efficiency of LED devices with a substrate increases by 67.75% over the extraction efficiency of those without a substrate. The light extraction efficiency of LED devices with a substrate increases by 113.55% when an additional patterned design is used on green and blue chips. The calculated large angle Delta u'v' can be as low as 0.015 for miniLED devices. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
In vivo functional photoacoustic micro-imaging of the electrically stimulated rat brain with multi-wavelengths
(2010)
Liao, Lun-De
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Li, Meng-Lin
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Lai, Hsin-Yi
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Chen, You-Yin
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Chao, Paul C. -P.
In this study, we report on using multi-wavelength photoacoustic microscopy to image hemodynamic changes of total hemoglobin concentration (HbT) (i.e., blood volume) and oxygenation (SO(2)) in rat brain cortex vessels with electrical stimulation. Electrical stimulation of the rat left forelimb was applied to evoke changes in vascular dynamics of the rat somatosensory cortex. The applied current pulses were with a pulse frequency of 3 Hz, pulse duration of 0.2 ms, and pulse amplitude of 5 mA, respectively. The imaging target of rat brains was demarcated at AP 0 - -2.5 mm and ML +/-6 mm with respect to bregma. HbT changes were probed by images acquired at 570 nm, a hemoglobin isosbestic point while SO(2) changes were imaged by those acquired at 560 nm or 600 nm and their derivatives, which were normalized to those with 570 nm wavelengths. Correlation between the electrical stimulation paradigm and images acquired at 570, 560, and 600 nm in contralateral and ipsilateral vasculature was statistically analyzed, showing that the HbT and SO(2) changes revealed by multi-wavelength photoacoustic images spatially correlated with contralateral vasculature.
The photonic properties of micro/mini LED arrays with different substrate thickness
(2020-01-01)
Yang, Shu-Mei
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Wang, Po-Hsun
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Chao, Chia-Hsin
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Chu, Chun-Wen
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Chen, Yu-Sheng
In this study, we review our progress in micro/mini LED arrays and their numerical simulation in optical fields. The variation in substrate thickness will be included in the calculation and the results can provide detailed insight for the optimization of the micro/mini LED structures.
Transcranial imaging of functional cerebral hemodynamic changes in single blood vessels using in vivo photoacoustic microscopy
(2012-06-01)
Liao, Lun-De
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Lin, Chin-Teng
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Shih, Yen-Yu I.
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Duong, Timothy Q.
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Lai, Hsin-Yi
Optical imaging of changes in total hemoglobin concentration (HbT), cerebral blood volume (CBV), and hemoglobin oxygen saturation (SO2) provides a means to investigate brain hemodynamic regulation. However, high-resolution transcranial imaging remains challenging. In this study, we applied a novel functional photoacoustic microscopy technique to probe the responses of single cortical vessels to left forepaw electrical stimulation in mice with intact skulls. Functional changes in HbT, CBV, and SO2 in the superior sagittal sinus and different-sized arterioles from the anterior cerebral artery system were bilaterally imaged with unambiguous 36x65-mu m(2) spatial resolution. In addition, an early decrease of SO2 in single blood vessels during activation (i.e., 'the initial dip') was observed. Our results indicate that the initial dip occurred specifically in small arterioles of activated regions but not in large veins. This technique complements other existing imaging approaches for the investigation of the hemodynamic responses in single cerebral blood vessels. Journal of Cerebral Blood Flow & Metabolism (2012) 32, 938-951; doi:10.1038/jcbfm.2012.42; published online 4 April 2012