Browsing by Author "Chen, Hsiu-Cheng"

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A block copolymer enhances the efficiency of small-molecule bulk-heterojunction photovoltaics
(2016-01-01)
Chen, Hsiu-Cheng
;
Su, Yu-Wei
;
Wei, Kung-Hwa
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Block copolymers can self-assemble into ordered structures having feature dimensions on the order of 10 to 100 nm; we took advantage of the different polarities of the blocks of a low-molecular-weight diblock copolymer polystyrene-b-poly(ethylene oxide) (PS-b-PEO) that interact differentially with small molecules and fullerenes to tune the extent of phase separation in solution-processed small-molecule bulk-heterojunction (SMBHJ) solar cells. We incorporated small amounts of nanostructured PS-b-PEO to solar cells\' active layers featuring 7,7\'-{4,4-bis(2-ethylhexyl)-4H-silolo[3,2-b:4,5-b\']dithiophene-2,6-diyl} bis{6-fluoro-4-(5\'-hexyl-[2,2\'-bithiophen]-5-yl) benzo[c] [1,2,5]thiadiazole} (p-DTS(FBTTh2)(2)) and [6,6]-phenyl-C-71-butyric acid methyl ester (PC71BM) for optimizing the morphology and thus enhancing the devices\' power conversion efficiency. For understanding the effect of PS-b-PEO on the devices\' performances, we used synchrotron grazing-incidence wide-angle X-ray scattering, atomic force microscopy and transmission electron microscopy to probe and to decipher the morphologies of the resulting SMBHJ thin films. Without undergoing any annealing process, a device with an active layer of p-DTS(FBTTh2)(2): PC71BM (1.5 : 1, w/w) that incorporated 0.5 wt% of PS-b-PEO and was processed with a 1,8-diiodooctane solvent additive displayed a power conversion efficiency (PCE) of 7.3%, a relative increase of 2.5 times as compared to the PCE of 2.1% for the control device featuring only p-DTS(FBTTh2)(2) and PC71BM. Thus, incorporating this nanostructured block copolymer in the active layer allowed effective tuning of the small molecule active layer morphology and resulted in enhanced device efficiency.
A block copolymer enhances the efficiency of small-molecule bulk-heterojunction photovoltaics
(2016)
Chen, Hsiu-Cheng
;
Su, Yu-Wei
;
Wei, Kung-Hwa
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Block copolymers can self-assemble into ordered structures having feature dimensions on the order of 10 to 100 nm; we took advantage of the different polarities of the blocks of a low-molecular-weight diblock copolymer polystyrene-b-poly(ethylene oxide) (PS-b-PEO) that interact differentially with small molecules and fullerenes to tune the extent of phase separation in solution-processed small-molecule bulk-heterojunction (SMBHJ) solar cells. We incorporated small amounts of nanostructured PS-b-PEO to solar cells\' active layers featuring 7,7\'-{4,4-bis(2-ethylhexyl)-4H-silolo[3,2-b:4,5-b\']dithiophene-2,6-diyl} bis{6-fluoro-4-(5\'-hexyl-[2,2\'-bithiophen]-5-yl) benzo[c] [1,2,5]thiadiazole} (p-DTS(FBTTh2)(2)) and [6,6]-phenyl-C-71-butyric acid methyl ester (PC71BM) for optimizing the morphology and thus enhancing the devices\' power conversion efficiency. For understanding the effect of PS-b-PEO on the devices\' performances, we used synchrotron grazing-incidence wide-angle X-ray scattering, atomic force microscopy and transmission electron microscopy to probe and to decipher the morphologies of the resulting SMBHJ thin films. Without undergoing any annealing process, a device with an active layer of p-DTS(FBTTh2)(2): PC71BM (1.5 : 1, w/w) that incorporated 0.5 wt% of PS-b-PEO and was processed with a 1,8-diiodooctane solvent additive displayed a power conversion efficiency (PCE) of 7.3%, a relative increase of 2.5 times as compared to the PCE of 2.1% for the control device featuring only p-DTS(FBTTh2)(2) and PC71BM. Thus, incorporating this nanostructured block copolymer in the active layer allowed effective tuning of the small molecule active layer morphology and resulted in enhanced device efficiency.
A nanostructured micellar diblock copolymer layer affects the memory characteristics and packing of pentacene molecules in non-volatile organic field-effect transistor memory devices
(2013)
Chen, Chia-Min
;
Liu, Chih-Ming
;
Tsai, Ming-Chang
;
Chen, Hsiu-Cheng
;
Wei, Kung-Hwa
Organic field-effect transistor (OFET) memory devices incorporating the copolymer polystyrene-block-poly(4-vinylpyridine) (PS56k-b-P4VP(8k)) layer, which features a thickness-dependent micellar nanostructure (P4VP-core, PS-shell), as a charge trapping layer can exhibit tunable memory windows for p-channel applications. For instance, the memory window increased substantially from 7.8 V for the device incorporating a 60 nm thick PS56k-b-P4VP(8k) layer to 21 V for the device incorporating a 27 nm thick layer, an increase of more than 2.5 times. Using simultaneous synchrotron grazing-incidence small-angle X-ray scattering and wide-angle X-ray scattering to probe the nanostructured micellar PS56k-b-P4VP(8k) layer and the pentacene layer positioned directly on the top of the copolymer layers, respectively, we were able to elucidate the structural characteristics of the bilayer and to correlate their effects with the memory performances of devices with similar architectures. For the PS56k-b-P4VP(8k) layers, we found that the inter-micelle distance and their lateral arrangements depended on the layer thickness: the thickness of the PS shells in the lateral direction decreased upon increasing the layer thickness, as did the memory window for the OFET device that incorporated the PS56k-b-P4VP(8k) layers, showing a strong dependence of the threshold voltage shifts (i.e., memory window) on the distance between the micelles. Additionally, for the molecular packing of the pentacene layer positioned on the copolymer layer, we found that the PS56k-b-P4VP(8k) layers affected not only the orientation of the pentacene molecules but also their grain sizes, thereby affecting the hole mobility of the memory devices. These results suggest that tuning the micellar nanostructure of the block copolymer thin film that was used as a trapping layer can be a simple and effective way for optimizing the memory window and affecting the hole mobility of OFET memory devices.
An universal electron transport layer involving hydrogen plasma-treated tungsten disulfide nanosheets doped zinc oxide layers for polymer donors with fullerene or small molecule acceptor photovoltaics
(2019-09-01)
Huang, Yi-Jiun
;
Yen, Po-Jen
;
Wang, Hao-Cheng
;
Chen, Hsiu-Cheng
;
Wei, Kung-Hwa
A new universal electron transport layer that involves doping hydrogen-plasma-treated tungsten disulfide (WS2) nanosheets into ZnO for polymer/fullerene or small molecule organic photovoltaics (OPVs) was prepared. A hydrogen plasma treatment was used to alter the structures of WS2 nanosheets such that the W6+ content was converted into W4+; then ZnO:WS2 nanosheets composites were prepared to form electron transport layers (ETLs). The energy band of the ZnO:WS2 films could be tuned from 5.15 to 4.60 eV by varying the concentration of the WS2 nanosheets up to 0.5 wt%. It was found that ZnO:WS2 ETLs exhibited superior charge transport properties than those of the pristine ZnO layer because of the structure changes, as determined from the X-ray scattering characterizations. OPVs incorporating active layers of PTB7-TH/PC71BM and PTB7-TH/IDIC blends exhibited their power conversion efficiencies of 10.3% and 6.7%, respectively, with the incorporation of 0.3 wt% of the WS2 nanosheets, up from 8.9% to 5.4% for the corresponding devices featuring pristine ZnO-relative increases of 16% and 24%, respectively. This study demonstrates the effectiveness of hydrogen plasma treatment for altering the surface structures of two-dimensional transition-metal-dichalcogenide nanosheets, and paves a way for the composite electron transport layers for use in organic photovoltaics.
Block Copolymer-Tuned Fullerene Electron Transport Layer Enhances the Efficiency of Perovskite Photovoltaics
(2016-09-21)
Lin, Hsi-Kuei
;
Su, Yu-Wei
;
Chen, Hsiu-Cheng
;
Huang, Yi-Jiun
;
Wei, Kung-Hwa
In this study, we enhanced the power conversion efficiency (PCE) of perovskite solar cells by employing an electron transfer layer (ETL) comprising [6,6]phenyl-C-61-butyric acid methyl ester (PC61BM) and, to optimize its morphology, a small amount of the block copolymer polystyreneb-poly(ethylene oxide) (PS-b-PEO), positioned on the perovskite active layer. When incorporating 0.373 wt, % PS-b-PEO into PC61BM, the PCE of the perovskite photovoltaic device increased from- 9.4% to 13.4%, a relative increase of 43%, because of a large enhancement in the fill factor of the device. To\' decipher the intricate morphology of the ETL, we used synchrdtron grazing-incidence small-angle X-ray scattering for determining the PC61BM cluster site, atomic force microscopy and scanning electron microscopy for probing the-surface, and transmission electron microscopy for observing the aggregation of PC61BM in the ETL. We found that the interaction between PS-b-PEO and PC61BM resulted in smaller PC61BM dusters that further aggregated into dendritic structures in some domains, a result of the similar polarities of the PS block and PC61BM; this behavior could \'be used to tune the morphology of the ETL. The optimal PS-b-PEO-mediated PC61BM cluster size in the ETT, was 17 nm, a large reduction from 59 nin for the pristine PC61BM layer. This approach ofincorporating a small amount of nanostructured block copolymer into a fullerene allowed us to effectively tune the morphology of the ETL on the perovskite active layer and resulted in enhanced fill factors of the devices and thus their device efficiency.
Complementary solvent additives tune the orientation of polymer lamellae, reduce the sizes of aggregated fullerene domains, and enhance the performance of bulk heterojunction solar cells
(2014-01-01)
Liu, Chih-Ming
;
Su, Yu-Wei
;
Jiang, Jian-Ming
;
Chen, Hsiu-Cheng
;
Lin, Shu-Wei
In this study we employed 1-chloronaphthalene (CN) and 1,8-diiodooctane (DIO) as binary additives exhibiting complementarily preferential solubility for processing the crystalline conjugated polymer poly[bis(dodecyl)thiophene-dodecyl-thieno[3,4-c]pyrrole-4,6-dione] (PBTC12TPD) and the fullerene [6,6]-phenyl-C-71-butyric acid methyl ester (PC71BM) in chloroform. Using synchrotron grazing-incidence small-/wide-angle X-ray scattering and transmission electron microscopy to analyse the structure of the PBTC12TPD-PC71BM blend films, we found that the binary additives with different volume ratios in the processing solvent allow us to tune the relative population of face-on to edge-on PBTC12TPD lamellae and the size of PC71BM clusters in the blend films; the sizes of the fractal-like PC71BM clusters and the aggregated domains of PC71BM clusters increased and decreased, respectively, upon increasing the amount of DIO, whereas the relative ratio of face-on to edge-on PBTC12TPD lamellae increased upon increasing the amount of CN. When fabricating the photovoltaic devices, the short-circuit current density of the devices with the PBTC12TPD-PC71BM active layer having been processed with the binary additives is higher than that of the device incorporating an active layer processed without any additive. As a result, the power conversion efficiency of a device incorporating an active layer of PBTC12TPD-PC71BM (1 : 1.5, w/w) processed with binary additives of 0.5% DIO and 1% CN in chloroform increased to 6.8% from a value of 4.9%, a relative increase of 40%, for the corresponding device containing the same active layer but processed without any additive.
Conjugated random copolymers of benzodithiophene-benzooxadiazole-diketopyrrolopyrrole with full visible light absorption for bulk heterojunction solar cells
(2013)
Jiang, Jian-Ming
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Chen, Hsiu-Cheng
;
Lin, His-Kuei
;
Yu, Chia-Ming
;
Lan, Shang-Che
We have used Stille coupling polymerization to synthesize a series of new donor-acceptor (D-A) conjugated random copolymers-PBDTT-BO-DPP-that comprise electron-rich alkylthienyl-substituted benzodithiophene (BDTT) units in conjugation with electron-deficient 2,1,3-benzooxadiazole (BO) and diketopyrrolopyrrole (DPP) moieties that have complementary light absorption behavior. These polymers exhibited excellent thermal stability with thermal degrading temperatures higher than 340 degrees C. Each of these copolymers exhibited (i) broad visible light absorption from 400 to 900 nm and (ii) a low optical band gap that is smaller than 1.4 eV and a low-lying highest occupied molecular orbital that is deeper than -5.22 eV. As a result, bulk heterojunction photovoltaic devices derived from these polymers and fullerenes provided a high short-circuit current density that is larger than 12 mA cm(-2). In particular, a photovoltaic device prepared from the PBDTT-BO-DPP (molar ratio, 1 : 0.5 : 0.5)/PC71BM (w/w, 1 : 2) blend system with 1-chloronaphthalene (1 volume%) as an additive exhibited excellent photovoltaic performance, with a value of V-oc of 0.73 V, a high short-circuit current density of 17 mA cm(-2), a fill factor of 0.55, and a promising power conversion efficiency of 6.8%, indicating that complementary light-absorption random polymer structures have great potential for increasing the photocurrent in bulk heterojunction photovoltaic devices.
Doping ZnO Electron Transport Layers with MoS2 Nanosheets Enhances the Efficiency of Polymer Solar Cells
(2018-06-13)
Huang, Yi-Jiun
;
Chen, Hsiu-Cheng
;
Lin, Hsi-Kuei
;
Wei, Kung-Hwa
;
材料科學與工程學系
In this study, we incorporated molybdenum disulfide (MoS2) nanosheets into sol-gel processing of zinc oxide (ZnO) to form ZnO:MoS2 composites for use as electron transport layers (ETLs) in inverted polymer solar cells featuring a binary bulk heterojunction active layer. We could effectively tune the energy band of the ZnO:MoS2 composite film from 4.45 to 4.22 eV by varying the content of MoS2 up to 0.5 wt %, such that the composite was suitable for use in bulk heterojunction photovoltaic devices based on poly [bis (5-(2- ethylhexyl) thi en-2-yl)benzo dithiophene-alt-(4-(2-ethylhexyl)-3-fluorothienothiophene)-2-carboxylate-2,6-diyl] (PTB7-TH)/phenyl-C-71-butryric acid methyl ester (PC71BM). In particular, the power conversion efficiency (PCE) of the PTB7-TH/PC71 BM (1:1.5, w/w) device incorporating the ZnO:MoS2 (0.5 wt %) composite layer as the ETL was 10.1%, up from 8.8% for the corresponding device featuring ZnO alone as the ETL, a relative increase of 15%. Incorporating a small amount of MoS2 nanosheets into the ETL altered the morphology of the ETL and resulted in enhanced current densities, fill factors, and PCEs for the devices. We used ultraviolet photoelectron spectroscopy, synchrotron grazing incidence wide-/small-angle X-ray scattering, atomic force microscopy, and transmission electron microscopy to characterize the energy band structures, internal structures, surface roughness, and morphologies, respectively, of the ZnO:MoS2 composite films.
Effects of bulk and interfacial charge accumulation on fill factor in organic solar cells
(2013-05-13)
Chen, Bingbing
;
Qiao, Xianfeng
;
Liu, Chih-Ming
;
Zhao, Chen
;
Chen, Hsiu-Cheng
The effects of charge accumulation on fill factor (FF) are studied by using light intensity-dependent current-voltage and capacitance-voltage measurements based on poly-{bi(dodecyl) thiophene-thieno[ 3,4-c]pyrrole-4,6-dione}:1(3-methyloxycarbonyl)propyl-1-phenyl [6,6] (PBTTPD:PCBM) solar cells. We find that the FF of un-annealed device shows a non-monotonic dependence of light intensity: first an increase and then a decrease with increasing light intensity. This suggests that both bulk charge accumulation and recombination determine the FF before thermal annealing. Furthermore, the morphological enhancement of PBTTPD: PCBM film leads to a monotonic decrease of FF as increasing light intensity. This indicates that only surface charge accumulation plays an important role in the determination of the FF after thermal annealing. (C) 2013 AIP Publishing LLC.
Energy transfer within small molecule/conjugated polymer blends enhances photovoltaic efficiency
(2017-09-14)
Lin, Yu-Che
;
Su, Yu-Wei
;
Li, Jia-Xing
;
Lin, Bo-Hsien
;
Chen, Chung-Hao
In this study, we employed ternary blends capable of energy transfer-a synthesized high-band-gap small molecule (SM-4OMe) comprising benzodithiophene (BDT) and rhodanine units (a molecular structure that was designed for energy transfer), a low-band-gap polymer (PTB7-TH) comprising BDT and thienothiophene units with desired packing orientation, and a fullerene-as active layers for singlejunction photovoltaic devices. The light absorption of the small molecule and the polymer was partially complementary, owing to their band gap difference, thereby broadening the absorption spectrum of solar light while maintaining the energy band structures that facilitated energy and charge transfer. The synthesized small molecule SM-4OMe and the PTB7-TH had somewhat similar chemical structureswith the same planar BDT donor units-and thus allowed sufficient mixing between them for energy transfer to take place. The power conversion efficiency of a device incorporating a ternary blend of PTB7-TH:SM-4OMe:PC71BM (0.9 :0.1 :1.5, w/w/w) as the active layer, processed with diiodooctane (2 vol%) in chlorobenzene, was 10.4%, which is higher than the value of 8% of the corresponding device incorporating PTB7-TH:PC71BM (1 :1.5, w/w)-an increase of 30%. We attribute this enhancement to the energy transfer from the high-band-gap small molecule SM-4OMe to the low-band-gap polymer PTB7-TH and to the optimal phase-separated bulk heterojunction morphology that comprises a mean PC71BM cluster size of 6 nm, which is lower than 12 nm for the PTB7-TH and PC71BM binary blends, and slightly better in-plane packing, arising from the inducements of the presence of SM-4OMe. This approach provides a facile and effective way to enhance the power conversion efficiency of single junction organic photovoltaics.
Enhancing performance of ternary blend photovoltaics by tuning the side chains of two-dimensional conjugated polymer
(2019-08-01)
Chen, Chung-Hao
;
Lu, Yi-Ju
;
Su, Yu-Wei
;
Lin, Yu-Che
;
Lin, Hsi-Kuei
We prepared the ternary blends active layer by incorporating a new two-dimensional donor-acceptor (D/A) conjugated polymer (BDTTBO) comprising benzo-dithiophene-thiophene-thiophene-benzo oxadiazole chemical units that has three different conjugated side chains bithiophene (BT), benzothiophene (BzT) and thienothiophene (TT) BDTTBO-BT, BDTTBO-BzT and BDTTBO-TT into poly (benzodithiophene-fluorothienothiophene) (PTB7-TH) and PC71BM as for organic photovoltaics (OPVs). We expected that incorporating these BDTTBO with different side chains into the blend of PTB7-TH and PC71BM not only can broaden the absorption of solar spectrum thereby increasing short-circuit current density but also tune the packing of PTB7-TH and the dispersion of PC71BM. In particular, we found that incorporating 10% of BDTTBO-BT to form the PTB7-TH:BDTTBO-BT:PC71BM ternary blend (active layer) device could improve the power conversion efficiency to 10.4% from 9.0% for the binary blend of PTB7-TH:PC71BM device-a relative increase of 15%. We examined the packing orientations of the PBDTTBO:PTB7-TH:PC71BM ternary blend films using synchrotron two-dimensional grazing-incidence wide-angle X-ray scattering, and found that the incorporation of 10% relatively higher crystallinity PBDTTBO-BT, PBDTTBO-BzT or PBDTTBO-TT not only altered the packing orientation of PTB7-TH substantially but also reduced PC71BM cluster size in the ternary blend system, as compared to that in the case of PTB7-TH with PC71BM binary blend, thereby providing more pathways for electrons and thus enhancing the carrier transport in the ternary blend, as evidenced by the carrier mobility.
Enhancing photovoltaic performance by tuning the domain sizes of a small-molecule acceptor by side-chain-engineered polymer donors
(2019-02-21)
Lin, Yu-Che
;
Lu, Yi-Ju
;
Tsao, Cheng-Si
;
Saeki, Akinori
;
Li, Jia-Xing
This paper reports two new fluorine-substituted polymer donors (BO2FC8, BO2FEH), with different side-chain architectures, and a new chlorine-substituted small-molecule acceptor (m-ITIC-OR-4Cl) that are capable of simultaneous charge and energy transfer as the binary blend active layer for organic photovoltaics. We first resolved the single-crystal structure of m-ITIC-OR-4Cl and then used simultaneous grazing-incidence wide-and small-angle X-ray scattering to decipher the multi-length-scale structures-such as the shape and size of aggregated domains and molecular orientation-of the blends of BO2FEH and BO2FC8 with m-ITIC-OR-4Cl. The linear side chains of BO2FC8 facilitated its packing and, thus, induced m-ITIC-OR-4Cl to form smaller disc-shaped aggregated domains (thickness: 2.9 nm) than its aggregate domain (thickness: 5.4 nm) in the blend of the branched BO2FEH. That is, the binary blend system of linear-side-chain BO2FC8 with m-ITIC-OR-4Cl featured larger interfacial areas and more pathways for charge transfer and transport, as evidenced by their carrier mobilities. The highest power conversion efficiency (PCE) of 11.0% was that for the BO2FC8: m-ITIC-OR-4Cl device, being consistent with the predicted PCE of 11.2% using machine learning based on random forest algorism; in comparison, the PCE of the BO2FEH:m-ITIC-OR-4Cl device was 6.4%. This study has not only provided insight into the photovoltaic performances of new polymer donor/small-molecule acceptor blends but has also, for the first time, deciphered the hierarchical morphologies-from molecule orientation to nano-domain shape and size-of such blend systems, linking the morphologies to the photovoltaic performances. The use of side-chain architectures suggests an approach for tuning the morphology of the polymer/small-molecule binary blend active layer for use in organic photovoltaics.
Molecular engineering of side chain architecture of conjugated polymers enhances performance of photovoltaics by tuning ternary blend structures
(2018-01-01)
Lin, Yu-Che
;
Cheng, Hao-Wen
;
Su, Yu-Wei
;
Lin, Bo-Hsien
;
Lu, Yi-Ju
Several approaches, including the use of small molecule acceptors, novel polymer structures, and tandem cell structures, have been adopted to prepare polymer solar cells displaying high power conversion efficiencies (PCEs). The application of ternary blends as the active layer for polymer solar cells-for which the absorption spectra can be tuned by varying the composition ratios of components-is another facile approach toward optimizing the PCEs of devices. The selection of suitable ternary blends active layer often relies on intuition and remains a formidable challenge. Here, we adopted a systemic approach of not only using the same donor chemical units in the two donor-acceptor (D/A) conjugated polymers with complementary light absorption (energy band gaps) but also varying the side chains architectures as a means of tuning the packing of these semi-planar conjugated polymers, thereby influencing the carrier transport and optimizing the PCE. We employed linear, branch and mixed linear-and-branch side-chain attached benzooxadiazole (BO) as the acceptor (A) units in poly [benzodithiophene-thiophene-benzooxadiazole] (PBDTTBO) conjugated polymers and monitored their interactions with poly[benzodithiophene-fluorothienothiophene] (PTB7-TH), both of which featured the same benzodithiophene (BDTT) donor (D) units. We found that incorporating a minor amount (10%) of D/A conjugated PBDTTBO with such side chains into the PTB7-TH with a fullerene allowed us to tune the packing of the two polymers and, thereby, enhance the PCEs of corresponding ternary blend devices; the PCE of the ternary blend device incorporating PBDTTBO with two branched-side chains, PTB7-TH, and PC71BM increased to 11.4% from 9.0% for the device incorporating only the binary blend of PTB7-TH and PC71BM-a relative increase of more than 25%. This approach of using side chain engineering to tune the structure of a minor conjugated polymer and, thus, influence the packing of another major conjugated polymer that features the same donor chemical units appears to be an effective means of preparing highly efficient polymer cells.
Photovoltaic performance of ladder-type indacenodithieno[3,2-b]thiophene-based polymers with alkoxyphenyl side chains
(2015-01-01)
Zang, Yue
;
Xu, Yun-Xiang
;
Chueh, Chu-Chen
;
Li, Chang-Zhi
;
Chen, Hsiu-Cheng
Two new ladder-type conjugated polymers, PIDTT-DFBT-EH and PIDTT-F-PhanQ-EH, are prepared through the copolymerization of heptacyclic IDTT with F-PhanQ and DFBT electron deficient moieties. The introduction of 4-(2-ethylhexyloxy)-phenyl (EHOPh) side-chains onto the polymer is beneficial for achieving high molecular weight and good solution-processability of materials. The derived polymer solar cells yielded PCEs of 5.48% (PIDTT-DFBT-EH) and 5.14% (PIDTT-F- PhanQ-EH), without engaging post-solvent or solvent additive treatments.
Plasma electrolysis allows the facile and efficient production of graphite oxide from recycled graphite
(2013)
Dang Van Than
;
Chen, Hsiu-Cheng
;
Li, Lain-Jong
;
Chu, Chih-Wei
;
Wei, Kung-Hwa
The production of graphite oxide from graphite usually requires strong oxidants, concentrated acids, and a reaction time of the order of 100 h. In this study, we adopted a highly efficient cathodic plasma (CP) process in which the vapor plasma envelope calorific effect provides instant oxidation and expansion of graphite for producing plasma-expanded graphite oxides (PEGOs) from recycled graphite electrodes (GEs) or high purity graphite (HG), within a reaction time of 10 min without the need for strong oxidants or concentrated acids. X-ray diffraction, X-ray photoelectron spectroscopy and Raman spectroscopy confirmed the dramatic structural change from GEs or HG to graphite oxides after the CP process. Furthermore, scanning electron microscopy and transmission electron microscopy revealed that the graphite oxide possessed a spheroidal morphology, with dimensions of 1-3 mm, as a result of melting and subsequent quenching during the plasma electrolysis process. We obtained a stable, homogeneous dispersion of PEGOs in N-methyl-2-pyrrolidone after sonication and filtering of the centrifuged PEGOs. We used these spheroidal graphite oxide particles as effective adsorbents for the removal of pollutants (e. g., Methylene Blue) from aqueous solutions. These PEGOs also served as good precursors for the preparation of graphite nanoplatelets. CP processing appears to be an effective and environmentally friendly means for mass-producing graphite oxide.
Side Chain Structure Affects the Photovoltaic Performance of Two-Dimensional Conjugated Polymers
(2014-01-14)
Jiang, Jian-Ming
;
Lin, His-Kuei
;
Lin, Yu-Che
;
Chen, Hsiu-Cheng
;
Lan, Shang-Che
We used Stille coupling of electron-rich benzo[1,2-b:4,5-b']dithiophene (BDT) presenting conjugated alkylthiophene (T), alkylphenyl (P), or alkylfuran (F) side chains with electron-deficient alkoxy-modified 2,1,3-benzooxadiazole (BO) moieties to obtain a series of two-dimensional, conjugated, D-pi-A polymers (PBDTTBO, PBDTPBO, and PBDTFBO). The side chains of the BDT units altered the solubility, conformations, and electronic properties of the synthesized conjugated, polymers, allowing tuning of their photovoltaic properties when blended with fullerenes. Density functional theory calculations revealed that the presence of these side chain groups on the BDT donor units affected the torsion angles between the side chain groups and the conjugated main chains but resulted in only slightly different energy levels for the highest occupied molecular orbitals for these polymers, consistent with results obtained experimentally using cyclic voltammetry. These polymers displayed excellent thermal stabilities (5 wt % degradation temperatures: >330 degrees C) and broad spectral absorptions (from 450 to 700 nm). Transmission electron microscopy images revealed that the morphologies of active layers comprising these two-dimensional conjugated polymers and the fullerene derivative PC71BM did, however, vary substantially depending on the structure of the side chains that affects the solubility of the polymers. As a result, the efficiencies of photovoltaic devices incorporating PBDTFBO, PBDTPBO, or PBDTTBO polymers and PC71BM varied greatly, from 3.6 to 5.9%. When using 1-chloronaphthalene (1 vol %) or 1,8-diiodooctane (1 vol %) as an additive for processing the active layer, the power conversion efficiencies (PCEs) of photovoltaic devices incorporating blends of PBDTFBO, PBDTPBO, or PBDTTBO and PC71BM (1:2) improved to 5.4, 6.4, and 7.4%, respectively, due to their optimized morphologies, with the PCE of 7.4% being among the highest values reported for conjugated polymers involving BO moieties. Thus, the photovoltaic properties of these conjugated polymers were highly tunable through slight modifications of their side chain structures.
Solution-Processed Zinc Oxide/Polyethylenimine Nanocomposites as Tunable Electron Transport Layers for Highly Efficient Bulk Heterojunction Polymer Solar Cells
(2015-03-25)
Chen, Hsiu-Cheng
;
Lin, Shu-Wei
;
Jiang, Jian-Ming
;
Su, Yu-Wei
;
Wei, Kung-Hwa
In this study, we employed polyethylenimine-doped sol-gel-processed zinc oxide composites (ZnO:PEI) as efficient electron transport layers (ETL) for facilitating electron extraction in inverted polymer solar cells. Using ultraviolet photoelectron spectroscopy, synchrotron grazing-incidence small-angle X-ray scattering and transmission electron microscopy, we observed that ZnO:PEI composite films\' energy bands could be tuned considerably by varying the content of PEI up to 7 wt %-the conduction band ranged from 4.32 to 4.0 eV-and the structural order of ZnO in the ZnO:PEI thin films would be enhanced to align perpendicular to the ITO electrode, particularly at 7 wt % PEI, facilitating electron transport vertically. We then prepared two types of bulk heterojunction systems-based on poly(3-hexylthiophene) (P3HT):phenyl-C-61-butryric acid methyl ester (PC61BM) and benzo[1,2-b:4,5-b]dithiophene-thiophene-2,1,3-benzooxadiazole (PBDTTBO):phenyl-C-71-butryric acid methyl ester (PC71BM)-that incorporated the ZnO:PEI composite layers. When using a composite of ZnO:PEI (93:7, w/w) as the ETL, the power conversion efficiency (PCE) of the P3HT:PC61BM (1:1, w/w) device improved to 4.6% from a value of 3.7% for the corresponding device that incorporated pristine ZnO as the ETL-a relative increase of 24%. For the PBDTTBO:PC71BM (1:2, w/w) device featuring the same amount of PEI blended in the ETL, the PCE improved to 8.7% from a value of 7.3% for the corresponding device that featured pure ZnO as its ETL-a relative increase of 20%. Accordingly, ZnO:PEI composites can be effective ETLs within organic photovoltaics.
Synthesis, characterization, and photovoltaic properties of a low-bandgap copolymer based on 2,1,3-benzooxadiazole
(2011-01-01)
Jiang, Jian-Ming
;
Yang, Po-An
;
Chen, Hsiu-Cheng
;
Wei, Kung-Hwa
;
材料科學與工程學系
PBDTBO, a conjugated polymer comprising benzo[1,2-b:4,5-b']dithiophene (BDT) and 5,6-bis(octyloxy) benzo[c][1,2,5]-oxadiazole (BO) units, exhibits a deep HOMO energy level of -5.27 eV and excellent solubility. A device incorporating PBDTBO and [6,6]-phenyl-C(61)-butyric acid methyl ester (1 : 1, w/w) exhibited a power conversion efficiency of 5.7%.
Synthesis, characterization, and photovoltaic properties of a low-bandgap copolymer based on 2,1,3-benzooxadiazole
(2011-01-01)
Jiang, Jian-Ming
;
Yang, Po-An
;
Chen, Hsiu-Cheng
;
Wei, Kung-Hwa
;
材料科學與工程學系
PBDTBO, a conjugated polymer comprising benzo[1,2-b:4,5-b']dithiophene (BDT) and 5,6-bis(octyloxy) benzo[c][1,2,5]-oxadiazole (BO) units, exhibits a deep HOMO energy level of -5.27 eV and excellent solubility. A device incorporating PBDTBO and [6,6]-phenyl-C(61)-butyric acid methyl ester (1 : 1, w/w) exhibited a power conversion efficiency of 5.7%.