Browsing by Author "Chen, Fang-Chung"

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1-(3-Methoxycarbonyl)propyl-2-selenyl-[6,6]-methanofullerene as a n-Type Material for Organic Solar Cells
(2011-07-01)
Chuang, Shih-Ching
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Chiu, Chih-Wei
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Chien, Shang-Chieh
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Chu, Chih-Wei
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Chen, Fang-Chung
Demand for green and renewable energy is stimulating research into future materials for energy production. Thin films of materials possessing both electron accepting and donating functions play a unique role in solar energy technology because of their lightweight, flexibility, and economical, low-temperature, and large-area fabrication. A [60]fullerene derivative,[6,6]-2-selenyl-C(61)-butyric acid methyl ester (SeCBM), has been synthesized in three steps, namely through Friedel-Crafts acylation of selenophene, hydrazone formation and Bamford-Steven reaction. Organic photovoltaic device incorporating SeCBM and the conducting polymer P3HT exhibited an average power conversion efficiency of 3.26% and a champion efficiency as high as 3.81% under AM 1.5G irradiation. (C) 2011 Elsevier B.V. All rights reserved.
A single-substrate multicolor cholesteric liquid-crystal display prepared through ink-jet printing
(2009-10-01)
Lu, Jhih-Ping
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Chen, Fang-Chung
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Chen, Fu-Kang
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Hsu, Chen-Chun
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Liao, Yuan-Chang
Ink-jet printing was used to prepare a single-substrate multicolor cholesteric liquid-crystal (Ch-LC) display incorporating three Ch-LCs exhibiting different reflective wavelengths. A room-temperature low-vacuum chemical-vapor-deposition process was developed for coating a thin polymer film onto the Ch-LC so that the top electrode could be coated onto the Ch-LC layer. Herein, the successful operation of such a 10.4-in. QVGA Ch-LC display at 40 V will be described.
Accumulated plasmonic effects of gold nanoparticle-decorated PEGylated graphene oxides in organic light-emitting diodes
(2020-09-01)
Chuang, Ming-Kai
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Lin, Chun-Hao
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Chen, Fang-Chung
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交大名義發表
;
光電工程學系
Amphiphilic Au nanoparticle-decorated PEGylated graphene oxides (Au@PEG-GO) are used to construct multiple plasmonic nanostructures for enhancing the performance of organic light-emitting diodes (OLEDs). Because of the long side-chains of the Au@PEG-GO nanocomposites, the nanoparticles can be well dispersed both in organic and aqueous solvents, allowing them to be incorporated readily into the buffer layers, such as poly(3,4-ethylenedioxythiophene): polystyrenesulfonate (PEDOT:PSS) and the organic photoactive layers within OLEDs during the soultion processes. Herein, the Au@PEG-GO nanocomposites are blended into either the PEDOT:PSS or the emissive layer of OLEDs to trigger surface plasmonic effects, thereby improving the device efficiencies. The current efficiencies are improved by ca. 20% for both cases. More importantly, the simultaneous addition of the Au@PEG-GO nanocomposites into both layers leads to even pronounced plasmonic effects. Under the optimized condition, the current efficiency is enhanced by up to 38%, suggesting the plasmonic fields from both layers attributed to the device enhancement. We anticipate that the accumulated plasmonic effects originating from the multiple plasmonic nanostructures will open up new avenues for improving the performance of various solution-processed optoelectronic devices involving organic dyes.
Air Stable Ambipolar Organic Field-Effect Transistors and Complementary-Like Inverters Prepared with Surface-Modified Gate Dielectrics
(2009)
Chen, Fang-Chung
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Huang, Yu-Jen
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光電工程學系
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顯示科技研究所
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Department of Photonics
Air stable ambipolar organic field-effect transistors containing p/n heterojunctions are achieved by passivating the electron trapping sites on the SiO(2) surface. The morphology of the heterojunctions is controlled by the film thicknesses of p- and n-channel semiconductors, thereby affecting the device air stability and the electrical characteristics. Further, air stable complementary-like inverters, which are able to work both in the first and the third quadrants with a high gain up to 30, are also demonstrated.
Bandgap Engineering Enhances the Performance of Mixed-Cation Perovskite Materials for Indoor Photovoltaic Applications
(2019-10-01)
Wu, Ming-Ju
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Kuo, Chien-Chen
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Jhuang, Lu-Syuan
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Chen, Po-Han
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Lai, Yi-Fong
Indoor photovoltaics (IPVs) are attracting renewed interest because they can provide sustainable energy through the recycling of photon energy from household lighting facilities. Herein, the Shockley-Queisser model is used to calculate the upper limits of the power conversion efficiencies (PCEs) of perovskite solar cells (PeSCs) for two types of artificial light sources: fluorescent tubes (FTs) and white light-emitting diodes (WLEDs). An unusual zone is found in which the dependence of the PCEs on the bandgap (E-g) under illumination from the indoor lighting sources follows trends different from that under solar irradiation. In other words, IPVs exhibiting high performance under solar irradiation may not perform well under indoor lighting conditions. Furthermore, the ideal bandgap energy for harvesting photonic power from these indoor lighting sources is approximate to 1.9 eV-a value higher than that of common perovskite materials (e.g., for CH3NH3PbI3). Accordingly, Br- ions are added into the perovskite films to increase their values of E-g. A resulting PeSC featuring a wider bandgap exhibits PCEs of 25.94% and 25.12% under illumination from an FT and a WLED, respectively. Additionally, large-area (4 cm(2)) devices are prepared for which the PCE reaches approximate to 18% under indoor lighting conditions.
Bidentate chelating ligands as effective passivating materials for perovskite light-emitting diodes
(2019-04-21)
Hsiao, Ming-Chuan
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Chien, Ping-Cheng
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Jhuang, Lu-Syuan
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Chen, Fang-Chung
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交大名義發表
Herein, four pyridine-based chelating ligands, including 1,10-phenanthroline, 4,4-bipyridine, 4,7-diphenyl-1,10-phenanthroline (Bphen) and pyridine, are used as surface treatment agents for improving the electronic properties of perovskite materials. The results of the steady-state photoluminescence (PL), time resolved PL and hole-only devices made of CH3NH3PbBr3 thin films suggest that the traps are effectively passivated after post-deposition surface treatment with bidentate chelating ligands, including 1,10-phenanthroline and 4,4-bipyridine. Furthermore, the coordination capability of Bphen was suppressed which is probably due to its two additional phenyl groups, resulting in a steric hindrance effect. When compared with mono-dentate chelating pyridine, bidentate chelating ligands are more active in the current study. Finally, perovskite light-emitting diodes (PeLEDs) are fabricated and the devices exhibit a nearly doubled device efficiency after passivation with 1,10-phenanthroline. It is anticipated that the approach proposed here is a general method for improving the photonic properties of perovskite materials and the device performance of PeLEDs.
Cesium carbonate as a functional interlayer for polymer photovoltaic devices
(2008-05-15)
Chen, Fang-Chung
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Wu, Jyh-Lih
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Yang, Sidney S.
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Hsieh, Kuo-Huang
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Chen, Wen-Chang
The device characteristics of polymer solar cells with cesium carbonate (Cs(2)CO(3)) as an electron-injection interlayer have been investigated. It is found that the insertion of Cs(2)CO(3) at the cathode interface improves the device power conversion efficiency from 2.3% to 3.1%. In order to further understand the mechanism, the interfacial interaction between the active organic layer and the cathode was studied by x-ray photoemission spectroscopy (XPS). The results of XPS measurement indicate the fact that a portion of electrons transfer from the interlayer into the organic layer, resulting in n-type doping. The n-doping effect enhances the efficiency of electron injection and collection. Further, the maximum open-circuit voltage (V(oc)) was determined from its temperature dependence. For the device with Cs(2)CO(3), the maximum V(oc) is extremely close to the corresponding value of the energy difference between the highest occupied molecular orbital of the electron donor and the lowest unoccupied molecular orbital of the electron acceptor, suggesting a better Ohmic contact. All evidences indicated that Cs(2)CO(3) is a promising candidate as an interlayer to improve the device performance. (C) 2008 American Institute of Physics.
Chemically Doped and Cross-linked Hole-Transporting Materials as an Efficient Anode Buffer Layer for Polymer Solar Cells
(2011-11-22)
Sun, Ying
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Chien, Shang-Chieh
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Yip, Hin-Lap
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Zhang, Yong
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Chen, Kung-Shih
A series of cross-linkable hole-transporting materials (X-HTMs) consisting of indacenodithiophene, bithiophene, and thiophene units bookended by two triarylamine groups have been designed and synthesized to investigate their suitability as new anode buffer layer for bulk heterojunction polymer solar cells (PSCs). These X-HTMs can be thermally cross-linked at temperature between 150 and 180 C to form robust, solvent-resistant films for subsequent spin-coating of another upper layer. Energy levels of these cross-linked materials were measured by cyclic voltammetry, and the data suggest that these X-HTMs have desirable hole-collecting and electron-blocking abilities to function as an anode buffer layer for PSCs. In addition, by incorporating thiophene or fused ring units into the X-HTM backbone, it effectively improved the hole-carrier motilities. To further improve the conductivity and optical transparency for PSCs, the X-HTM films were p-doped with nitrosonium hexafluoroantimonate (NOSbF(6)). The doped X-HTM layers showed remarkably enhanced hole-current densities compared to neutral X-HTM under the same electric field bias. The properties of the doped X-HTM film as anode buffer layer has been investigated in PSCs. The resulting devices showed similar performance compared to those made using conducting polymer, poly(3,4-ethylene- dioxylenethiophene):poly(styrenesulfonate) (PEDOT:PSS), as the anode buffer layer. Moreover, a novel bilayer HTM structure consisting of a doped and a neutral layer was employed to exploit the feasibility of combining high conductivity from the doped X-HTM and good electron-blocking ability from the neutral X-HTM together. Interestingly, PSC devices based on this bilayer structure showed enhanced V(oc), J(sc), and FF compared to the devices with only a single-layer doped X-HTM. These results indicate that such X-HTMs are promising alternative materials to PEDOT:PSS as an anode buffer layer for polymer solar cells.
CMOS-Like Ambipolar Organic/Inorganic TFTs for AMLCD and AMOLED Applications
(2009)
Chu, Yi-Hsing
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Wu, Gao-Ming
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Chuang, Chiao-Shun
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Yu, Wei-Kuan
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Chen, Fang-Chung
Air-stable ambipolar thin-film transistors (TFTs) based on double active layer of pentacene / a-IGZO (amorphous In(2)O(3)Ga(2)O(3)-ZnO) have been fabricated on SiO(2)/p-Si substrates. The a-IGZO exhibits n-channel behavior, while pentacene presents p-channel characteristics. Most n-type organic materials are easily affected by moisture and oxygen, thus the measurement of ambipolar devices in ambience air is difficult. However, a-IGZO not only has outstanding mobility but also has good stability while being measured in ambient air. In our work, a CMOS-like inverter was constructed by using two identical ambipolar transistors and the voltage gain up to 70 was obtained. The inverter can be operated in both the first and the third quadrants simplifying circuit design for AMFPD applications.
Color filtering functional organic thin-film transistors
(2007)
Huang, Yu-Jen
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Chang, Hsiao-Fen
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Tsai, Shu-Ting
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Chuang, Chiao-Shun
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Cheng, Jung-An
The colored insulators were utilized as the color filter and the dielectric layer of the OTFTs simultaneously to obtain the desired color. This work was successfully integrated gate insulator and color filter, which offered an ink-jet printing compatible process for cost-effective fabrication of liquid-crystal displays.
Conjugated poly(fluoroalkyl 3-thienylacetate)s synthesized in supercritical carbon dioxide
(2012-04-01)
Keshtov, M. L.
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Lopatin, A. M.
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Marochkin, D. V.
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Chen, Fang-Chung
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Khokhlov, A. R.
Construction and characteristics of tandem organic solar cells featuring small molecule-based films on polymer-based subcells
(2010-01-20)
Chen, Fang-Chung
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Lin, Cheng-Hao
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光電工程學系
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顯示科技研究所
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Department of Photonics
In this study, we stacked a small molecule-based cell onto another polymer-based device to fabricate a tandem organic solar cell that extended the absorption range of the entire cell over a wider spectral range. Between the two subcells, we positioned a connecting structure comprising layers of Cs(2)CO(3), Ag and MoO(3). Current matching phenomena played an important role in determining the device efficiency. The judicious selection of subcells exhibiting superior current matching improved the performance of the tandem cell. Indeed, in the optimally performing tandem cells we obtained both a high open-circuit voltage (1.21 V) and an improved power conversion efficiency (1.81%). From analyses of the surface morphology and transmission spectra of the middle Ag layers, we deduced that the main function of this film was to provide more sites for efficient recombination of holes and electrons. The thickness of this layer was limited by its transmittance. A thinner Ag layer allowed more light to be harvested by the top cell, increasing the overall performance of the tandem cell.
Controllable lasing performance in solution-processed organic-inorganic hybrid perovskites
(2016)
Kao, Tsung Sheng
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Chou, Yu-Hsun
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Hong, Kuo-Bin
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Huang, Jiong-Fu
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Chou, Chun-Hsien
Solution-processed organic-inorganic perovskites are fascinating due to their remarkable photo-conversion efficiency and great potential in the cost-effective, versatile and large-scale manufacturing of opto-electronic devices. In this paper, we demonstrate that the perovskite nanocrystal sizes can be simply controlled by manipulating the precursor solution concentrations in a two-step sequential deposition process, thus achieving the feasible tunability of excitonic properties and lasing performance in hybrid metal-halide perovskites. The lasing threshold is at around 230 mu J cm(-2) in this solution-processed organic-inorganic lead-halide material, which is comparable to the colloidal quantum dot lasers. The efficient stimulated emission originates from the multiple random scattering provided by the micro-meter scale rugged morphology and polycrystalline grain boundaries. Thus the excitonic properties in perovskites exhibit high correlation with the formed morphology of the perovskite nanocrystals. Compared to the conventional lasers normally serving as a coherent light source, the perovskite random lasers are promising in making low-cost thin-film lasing devices for flexible and speckle-free imaging applications.
Copper phthalocyanine buffer layer to enhance the charge injection in organic thin-film transistors
(2007-02-12)
Chen, Fang-Chung
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Kung, Li-Jen
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Chen, Tung-Hsien
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Lin, Yung-Sheng
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光電工程學系
Copper phthalocyanine (CuPC) has been used as the buffer layer for source and drain electrodes to improve the performance of organic thin-film transistors. The mobility was improved by almost onefold after the modification. By incorporating with CuPC, the contact resistance was reduced, deduced from the line-transfer method. The higher hole current observed in the hole-only diode after adding CuPC further confirms the improvement of hole-injection efficiency. It is concluded that the device improvement is attributed to the reduction of contact resistance, which resulted from the Fermi level pinning at the induced gap states at the Au/CuPC interface. (c) 2007 American Institute of Physics.
Cross-Linkable Hole-Transport Materials Improve the Device Performance of Perovskite Light-Emitting Diodes
(2016-10-12)
Huang, Chiung-Fu
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Keshtov, Mukhamed L.
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Chen, Fang-Chung
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光電工程學系
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Department of Photonics
Hybrid organic/inorganic perovskites are promising candidate materials for use in photovoltaic applications. More recently, they have also become highly attractive as active materials for other optoelectronic devices, including lasers, light-emitting diodes, and photodetectors. Nevertheless, difficulties in forming continuous and uniform films and the existence of a charge-injection barrier between the perovskite layer and the electrodes have hindered the development of high-performance perovskite light-emitting diodes (PeLEDs). In this study, a cross-linked hole-transport layer (HTL) is introduced to improve the hole-injection efficiency of PeLEDs. Furthermore, this layer simultaneously facilitates the formation of smooth perovskite layers, presumably because of the different surface energies. More interestingly, the HTL also exhibits strong solvent effects on the device performance. When the processing solvent for fabricating the HTLs is changed from chlorobenzene to N,N-dimethylformamide (DMF), the perovskite layer becomes more uniform and continuous, leading to better surface coverage and higher device efficiency, presumably because DMF has strong affinity toward the perovskite precursors. The approach presented herein could become a general method for decreasing the hole-injection barrier of PeLEDs and, eventually, lead to higher device performance.
Differential Space-Limited Crystallization of Mixed-Cation Lead Iodide Single-Crystal Micro-Plates Enhances the Performance of Perovskite Solar Cells
(2019-10-01)
Sung, Hsin-Hung
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Kuo, Chien-Chen
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Chiang, Hung-Sheng
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Yue, Hong-Lin
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Chen, Fang-Chung
The synthesis of certain asymmetric perovskite single crystals (SCs)-including CH3NH3PbI3, which is used most commonly-for application in high-performance perovskite solar cells (PeSCs), remains very challenging. Herein, a promising but general method, differential space-limited crystallization (DSLC), is described for synthesizing high-quality perovskite single-crystal micro-plates. The thickness of the perovskite SCs is controlled by the difference between the thicknesses of two sets of polytetrafluoroethylene (PTFE) spacers. Because the DSLC method does not require very thin spacers, it simplifies the procedure of crystal growth. More importantly, the hydrophobicity of the PTFE spacers weakens the attraction between the surfaces of the confined space and the precursor complexes, thereby increasing the rate of diffusion of the precursor ions. Accordingly, the critical nucleation step is not limited by the low rate of diffusion of the ions. This approach is used to prepare mixed-cation lead iodide single-crystalline micro-plates for solar cell applications. The device performance of single-crystal PeSCs improves after introducing formamidinium ions. The stability of the single-crystal devices also improves relative to that of conventional thin-film counterparts. It is anticipated that this DSLC method can also be used to synthesize different types of asymmetrical perovskite SCs for other optoelectronic applications.
Effect of deposition temperature on the channel and contact resistance of pentacene thin-film transistors
(2007)
Chen, Ying-Pin
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Chen, Fang-Chung
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光電工程學系
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Department of Photonics
By varying the substrate temperature during the deposition of pentacene, the effect of temperature on the electrical performance of organic thin-film transistors, without serious disturbance of phase transition of pentacene, has been investigated. It has already understood that the device mobility goes up with temperature. The transfer line method is applied to find out the origin behind in the study. First, the channel resistance is more sensitive to the deposition temperature due to the difference size of grain. Second, among the two parts of parasitic resistance, the bulk resistance plays a more important role, and is less fluctuant to the deposition temperature. Furthermore, the contact resistance reduces with increasing deposition temperature, which is probably attributed from the difference of the molecular orientation.
Effect of the surface treatments on the turn-on voltage of penfecene-based than-film transistors
(2007)
Tsai, Shu-Ting
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Chen, Fang-Chung
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光電工程學系
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Department of Photonics
We employed three organic polymers (PMMA, PVP, and HMDS) to modify the surface of the inorganic dielectric, SiNx. Comparing the device with different treatments, the shift of the turn on voltage has been observed. It is inferred that the shift is due to the trapped charges in the insulator and interlayer between insulator and semiconductor.
Efficiency improvement of organic bifunctional devices by applying omnidirectional antireflection nanopillars
(2014)
Ho, Yu-Hsuan
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Liang, Hsun
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Liu, Shun-Wei
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Tian, Wei-Cheng
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Chen, Fang-Chung
OLED/OPV tandem devices have attracted great interest due to their various functions in green technology and potential sensing applications. Here we report a novel concept to improve the luminous efficiency and energy conversion efficiency of tandem bifunctional devices by integrating antireflection structures consisting of irregular nanopillars as the capping layer. The nanopillars were made on flexible polycarbonate substrates by using a nanoimprint method with an anodized aluminum oxide template. The average reflectivity of the patterned polycarbonate substrate at visible wavelengths was reduced to 3.3%. With the antireflection structures, the luminous intensity for bifunctional devices was improved by 41.9% compared to a device with a flat capping layer. The power conversion efficiency was improved from 0.48% to 0.61%, a 27.0% enhancement at normal incidence.
Efficient and stable polymer solar cells prepared using plasmonic graphene oxides as anode buffers
(2015-08-01)
Chen, Chung-Lei
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Chuang, Ming-Kai
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Chen, Chyong-Hua
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Chu, Chih-Wei
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Keshtov, Muchamed L.
Gold nanoparticle-decorated graphene oxides (AuNP-GOs) have been incorporated into inverted organic photovoltaic devices (OPVs) as anode interlayers. The OPVs fabricated with AuNP-GOs exhibited significant improvement in both the short-circuit current and fill factor compared to a reference device fabricated with neat GOs. We attribute the improvement in the efficiency of the device to the plasmonic effects of the AuNP-GO nanocomposites, which induced local enhancement of the electromagnetic field. More importantly, the inverted OPVs also exhibited better reliability after the use of AuNP-GO nanocomposites.