Browsing by Author "Chiu, Mao-Yuan"

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A Thieno[3,4-c]pyrrole-4,6-dione-Based Donor-Acceptor Polymer Exhibiting High Crystallinity for Photovoltaic Applications
(2010-09-14)
Yuan, Mao-Chuan
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Chiu, Mao-Yuan
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Liu, Shih-Pin
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Chen, Chia-Min
;
Wei, Kung-Hwa
An optical programming/electrical erasing memory device: Organic thin film transistors incorporating core/shell CdSe@ZnSe quantum dots and poly(3-hexylthiophene)
(2009-08-01)
Chiu, Mao-Yuan
;
Chen, Chen-Chia
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Sheu, Jeng-Tzong
;
Wei, Kung-Hwa
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材料科學與工程學系
An optical programming/electrical erasing memory device was fabricated by adopting organic thin film transistors incorporating core/shell CdSe@ZnSe quantum dots (QDs) and poly(3-hexylthiophene) (P3HT) as active layers. After illumination, the presence of quantum well-structured core/shell CdSe@ZnSe QDs within the P3HT film enhanced the maximum ON/OFF ratio substantially to 2700; this value was maintained for 8000 s without noticeable decay. The ON state current could be erased effectively when using a single pulse of the gate voltage (- 10 V). This fabrication approach opens up the possibility of improving the memory performance of polymeric materials prepared at low cost using simple processes, (C) 2009 Elsevier B.V. All rights reserved.
Competition between Fullerene Aggregation and Poly(3-hexylthiophene) Crystallization upon Annealing of Bulk Heterojunction Solar Cells
(2011-08-01)
Wu, Wei-Ru
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Jeng, U-Ser
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Su, Chun-Jen
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Wei, Kung-Hwa
;
Su, Ming-Shin
Concomitant development of [6,6]-phen-C(61)-butyric acid methyl ester (PCBM) aggregation and poly(3-hexylthiophene) (P3HT) crystallization in bulk heterojunction (BHJ) thin-film (ca. 85 nm) solar cells has been revealed using simultaneous grazing incidence small-/wide-angle X-ray scattering (GISAXS/GIWAXS). With enhanced time and spatial resolutions (5 s/frame; minimum q approximate to 0.004 angstrom(-1)), synchrotron GISAXS has captured In detail the fast growth in size of PCBM aggregates from 7 to 18 nm within 100 s of annealing at 150 degrees C. Simultaneously observed is the enhanced crystallization of P3HT Into lamellae oriented mainly perpendicular but also parallel to the substrate. An Avrami analysis of the observed structural evolution indicates that the faster PCBM aggregation follows a diffusion-controlled growth process (confined by P3HT segmental motion), whereas-the slower development of crystalline P3HT nanograins is characterized by constant nucleation rate (determined by the degree. of supercooling and POW demixing). These two competing kinetics result in local phase separation with space filling PCBM and P3HT nanodomains less than 20 nm in size when annealing temperature is kept below 180 degrees C. Accompanying the morphological development is the synchronized Increase In electron and hole mobilities of the BHJ thin-film solar cells, revealing the sensitivity of the carrier transport of the device on the structural features of PCBM and P3HT nanodomains. Optimized structural parameters, including the aggregate size and mean spacing of the PCBM aggregates, are quantitatively correlated to the device performance; a comprehensive network structure of the optimized BHJ thin film is presented.
Competition between PCBM Aggregation and P3HT crystallization in thin films upon annealing
(2011-01-01)
Jeng, U-Ser
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Wu, Wei-Ru
;
Su, Chun-Jen
;
Wei, Kung-Hwa
;
Su, Ming-Shin
Enhance photocurrent in poly(3-hexylthiophene)/gold nanoparticle composite films by gold surface plasmon resonance
(2007-03-25)
Chiu, Mao-Yuan
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Wei, Kung-Hwa
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材料科學與工程學系
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Department of Materials Science and Engineering
Morphologies of Self-Organizing Regioregular Conjugated Polymer/Fullerene Aggregates in Thin Film Solar Cells
(2010-01-12)
Chiu, Mao-Yuan
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Jeng, U-Ser
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Su, Ming-Shin
;
Wei, Kung-Hwa
;
材料科學與工程學系
In this study, We used simultaneous synchrotron grazing incidence X-ray scattering and diffraction to elucidate the overall morphologies of bulk heterojunction (BHJ) thin film (ca. 100 nm) solar cells containing phase-separated poly(3-hexylthiophene) (P3HT) and [6,6]-phertyl-C(61)-butyric acid methyl ester (PCBM) domains. Specifically, the dimensions and orientation of the P3HT crystallites and the sizes of the PCBM aggregates in BHJ thin films were determined. The appropriate PCBM aggregate size and density required for all optimum performance of the film in the photovoltaics device resulted in deteriorated ordering in the out-of-plane direction, but improved the in-plane packing of the P3HT lamellae. When the P3HT crystallites and PCBM aggregates had comparable domain sizes and number densities, the interpercolated networks for electron- and hole-transport were optimized in the film. This new understanding of the underlying mechanism of carrier mobility in BHJ thin films might be crucial in improving the efficiency of future solar cells.
Nano-scale Morphology for Bulk Heterojunction Polymer Solar Cells
(2015)
Su, Yu-Wei
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Chiu, Mao-Yuan
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Wei, Kung-Hwa
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材料科學與工程學系
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Department of Materials Science and Engineering
In any high performance polymer solar cell, the morphology is always an important aspect. The bulk-heterojunction morphology is a challenging research area, which is the focus of this chapter. Many characterization techniques have been used to investigate the BHJ morphologies of active layers in OPVs; which can be classified into reciprocal-space and real-space techniques. We will discuss both the reciprocal-space techniques generally used to obtain spatially averaged information (X-ray or neutron scattering), as well as real-space techniques for analyzing the phase separation and aggregation of BHJ morphology. Our focus will be on how X-ray scattering and transmission electron microscopy based characterization techniques can be used to analyze the effects of the relative length scales of PCBM clusters and polymer (P3HT as example) crystallites on device performance.
Photoresponses and memory effects in organic thin film transistors incorporating poly(3-hexylthiophene)/CdSe quantum dots
(2008-04-07)
Chen, Chen-Chia
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Chiu, Mao-Yuan
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Sheu, Jeng-Tzong
;
Wei, Kung-Hwa
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材料科學與工程學系
This paper describes the optical responses and memory effects of poly(3-hexylthiophene) (P3HT)/CdSe quantum dot (QD) thin-film transistors (TFTs). TFTs incorporating P3HT/CdSe QD blends as the active layer exhibited higher photocurrents than did the corresponding P3HT-only devices because the heterojunction between P3HT and the CdSe QDs enhanced the separation of excitons. Moreover, the CdSe QDs served as trap centers so that the memory effect was maintained for several hours, even when the device was operated without a gating voltage. Here, we demonstrate the potential applicability of such P3HT/CdSe QD TFTs through repeated optical programming and electrical erasing. (C) 2008 American Institute of Physics.
Simultaneous use of small- and wide-angle X-ray techniques to analyze nanometerscale phase separation in polymer heterojunction solar cells
(2008-07-02)
Chiu, Mao-Yuan
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Jeng, U-Ser
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Su, Chiu-Hun
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Liang, Keng S.
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Wei, Kung-Hwa
Using grazing-incidence small-angle X-ray scattering and wide-angle X-ray diffraction techniques to analyze the nanoscale phase separation of P3HT and PCBM after annealing, the effects of the sizes of the PCBM clusters and P3HT crystallites on the power conversion efficiency of bulk heterojunction solar cells are studied.
Surface and interface porosity of polymer/fullerene-derivative thin films revealed by contrast variation of neutron and X-ray reflectivity
(2011)
Liu, Heng-Jui
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Jeng, U-Ser
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Yamada, Norifumi L.
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Su, An-Chung
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Wu, Wei-Ru
Contrast variation of neutron and X-ray reflections has been adapted to reveal the film in-depth (vertical) composition profiles of the blend of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) for bulk heterojunction thin-film solar cells, with a PCBM/P3HT weight ratio of c = 0.6, 0.8 and 1.0. The X-ray scattering-length-density (SLD) profiles, extracted from X-ray reflectivity for the blend films spun-cast on Si wafer, exhibit a stratified film morphology of ca. 85 nm film thickness; the corresponding neutron SLD profiles extracted for the same films further elucidate a PCBM-enriched interfacial layer adjacent to the Si substrate. In contrast to the often assumed two-phase model, a three-phase model with porosity included as the third phase has to be used in deducing the absolute volume fractions of PCBM and P3HT from the complementary neutron and X-ray SLD profiles. In general, the thus deduced in-depth composition profiles for the blend films comprise a substantial surface layer (10-15 nm) of ca. 40% porosity, a 50 nm main layer with relatively uniform PCBM-P3HT composition, and a PCBM-enriched interface layer (similar to 20 nm) with similar to 15% porosity. Formation of the surface porosity is related to interfacial instability occurred in a transient surface layer upon film drying. Annealing at 150 degrees C influences modestly the vertical phase separation of the film, but drastically activates local phase separation for formation and growth of PCBM and P3HT nanodomains, as revealed by grazing incidence small/wide angle X-ray scattering. The surface/interface porosity features (overlooked in nearly all the previous studies) and the composition-dependent vertical phase separation bear hints in advancing device performance via interfacial morphology optimization.
Synthesis and Characterization of Donor-Bridge-Acceptor Alternating Copolymers Containing Perylene Diimide Units and Their Application to Photovoltaic Cells
(2010-03-15)
Yuan, Mao-Chuan
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Su, Ming-Hsin
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Chiu, Mao-Yuan
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Wei, Kung-Hwa
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材料科學與工程學系
We have used Suzuki coupling to prepare a series of alternating copolymers featuring coplanar cyclopentadithiophene and hole-transporting carbazole units. We observed quenching in the photoluminescence spectra of our polymers after incorporating pendent electron-deficient perylene diimide (PDI) moieties on the side chains, indicating more efficient photoinduced electron transfer. Electrochemical measurements revealed that the PDI-containing copolymers displayed reasonable and sufficient offsets of the energy levels of their lowest unoccupied molecular orbitals for efficient charge dissociation. The performance of bulk heterojunction photovoltaic cells incorporating the copolymer/[6,6]-phenyl-C(61)-butyric acid methyl ester blends (1:4, w/w) was optimized when the active layer had a thickness of 70 nm. The photocurrents of the devices were enhanced as a result of the presence of the PDI moieties, thereby leading to improved power conversion efficiencies. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1298-1309, 2010
Synthesis and Characterization of Pyrido[3,4-b]pyrazine-Based Low-Bandgap Copolymers for Bulk Heterojunction Solar Cells
(2010-08-10)
Yuan, Mao-Chuan
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Chiu, Mao-Yuan
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Chiang, Chien-Ming
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Wei, Kung-Hwa
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材料科學與工程學系
We have used Stille polycondensation to prepare a series of low-bandgap copolymers, P1-P4, by conjugating the electron-accepting pyrido[3,4-b]pyrazine (PP) moieties with the electron-rich benzo[1,2-b:3,4-b']dithiophene (BDT) or cyclopentadithiophene (CPDT) units. P1 and P3 are based on PP and BDT units while P2 and P4 are based on PP and CPDT units. All of these polymers exhibited excellent thermal stability and sufficient energy offsets for efficient charge transfer and dissociation, as determined through thermogravimetric analyses and cyclic voltammetry, respectively. The bandgaps of the polymers could be tuned in the range 1.46-1.60 eV by using the two different donors, which have different electron-donating abilities. The three-component copolymers, P3 and P4, incorporating the thiophene and bithiophene segments, respectively, absorbed broadly, covering the solar spectrum from 350 to 800 nm. The morphologies of the blends of P3 and P4 with [6,6]-phenyl-C(70)-butyric acid methyl ester (PC(70)BM) were more homogeneous than those of P1 and P2; in addition, devices incorporating the P3 and P4 blends exhibited superior performance. The best device performance resulted from an active layer containing the P4:PC(70)BM blend; the short-circuit current was 10.85 mA cm(-2) and the power conversion efficiency was 3.15%.