Browsing by Author "Su, Yu-Wei"

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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.
Acoustic realigment of nematic liquid crystals by guided waves
(2007)
Lee, Yu-Ching
;
Shih, Wun-Bin
;
Su, Yu-Wei
;
Yin, Ching-Chung
;
機械工程學系
This paper presents an experimental evidence to correlate the acousto-optic effect of nematic liquid crystals to modal excitations of guided acoustic waves. The optic axes of liquid crystal molecules in a cell can be tilted by ultrasound at oblique incidence. The cell filled with homeotropically aligned liquid crystal material, 5CB, is fully immersed in a water tank situated between two crossed polarizers. Multi-modal guided acoustic waves have been excited in cell by changing the angle of incidence and driving frequency. The liquid crystal material sandwiched between two glass plates is regarded as a Newtonian fluid and modeled to be an isotropic hypothetical solid. The phase velocity dispersion curves and associated modal strains within the liquid crystal cell are determined numerically. Comparison between measured data and prediction reveals that guided acoustic waves have influence on the acousto-optic response of liquid crystals rather than bulk acoustic waves. Simulated results show that homeotropically and homogeneously aligned liquid crystals can be affected by symmetric and antisymmetric modes, respectively.
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 Polymer/Nanocrystal Nanocomposites for Renewable Energy Applications in Photovoltaics and Photocatalysis
(2014-11-26)
Su, Yu-Wei
;
Lin, Wei-Hao
;
Hsu, Yung-Jung
;
Wei, Kung-Hwa
;
材料科學與工程學系
Conjugated polymer/nanocrystal composites have attracted much attention for use in renewable energy applications because of their versatile and synergistic optical and electronic properties. Upon absorbing photons, charge separation occurs in the nanocrystals, generating electrons and holes for photocurrent flow or reduction/oxidation (redox) reactions under proper conditions. Incorporating these nanocrystals into conjugated polymers can complement the visible light absorption range of the polymers for photovoltaics applications or allow the polymers to sensitize or immobilize the nanocrystals for photocatalysis. Here, the current developments of conjugated polymer/nanocrystal nanocomposites for bulk heterojunction-type photovoltaics incorporating Cd- and Pb-based nanocrystals or quantum dots are reviewed. The effects of manipulating the organic ligands and the concentration of the nanocrystal precursor, critical factors that affect the shape and aggregation of the nanocrystals, are also discussed. In the conclusion, the mechanisms through which conjugated polymers can sensitize semiconductor nanocrystals (TiO2, ZnO) to ensure efficient charge separation, as well as how they can support immobilized nanocrystals for use in photocatalysis, are addressed.
Distribution of Crystalline Polymer and Fullerene Clusters in Both Horizontal and Vertical Directions of High-Efficiency Bulk Heterojunction Solar Cells
(2013-06-26)
Liu, Chih-Ming
;
Su, Ming-Shin
;
Jiang, Jian-Ming
;
Su, Yu-Wei
;
Su, Chun-Jen
In this study, we used (i) synchrotron grazing-incidence small-/wide-angle X-ray scattering to elucidate the crystallinity of the polymer PBTC12TPD and the sizes of the clusters of the fullerenes PC61BM and ThC61BM and (ii) transmission electron microscopy/electron energy loss spectroscopy to decipher both horizontal and vertical distributions of fullerenes in PBTC12TPD/fullerene films processed with chloroform, chlorobenzene and dichlorobezene. We found that the crystallinity of the polymer and the sizes along with the distributions of the fullerene clusters were critically dependent on the solubility of the polymer in the processing solvent when the solubility of fullerenes is much higher than that of the polymer in the solvent. In particular, with chloroform (CF) as the processing solvent, the polymer and fullerene units in the PBTC12TPD/ThC61BM layer not only give rise to higher crystallinity and a more uniform and finer fullerene cluster dispersion but also formed nanometer scale interpenetrating network structures and presented a gradient in the distribution of the fullerene clusters and polymer, with a higher polymer density near the anode and a higher fullerene density near the cathode. As a result of combined contributions from the enhanced polymer crystallinity, finer and more uniform fullerene dispersion and gradient distributions, both the short current density and the fill factor for the device incorporating the CF-processed active layer increase substantially over that of the device incorporating a dichlorobenzene-processed active layer; the resulting power conversion efficiency of the device incorporating the CF-processed active layer was enhanced by 46% relative to that of the device incorporating a dichlorobenzene-processed active layer.
Dual nanocomposite carrier transport layers enhance the efficiency of planar perovskite photovoltaics
(2018-01-01)
Lin, Hsi-Kuei
;
Li, Jia-Xing
;
Wang, Hao-Cheng
;
Su, Yu-Wei
;
Wu, Kaung-Hsiung
In photovoltaic devices, more effective transfer of dissociated electrons and holes from the active layer to the respective electrodes will result in higher fill factors and short-circuit current densities and, thus, enhanced power conversion efficiencies (PCEs). Planar perovskite photovoltaics feature an active layer that can provide a large exciton diffusion length, reaching several micrometers, but require efficient carrier transport layers for charge extraction. In this study, we employed two nanocomposite carrier transfer layersan electron transport layer (ETL) comprising [6,6]phenyl-C-61-butyric acid methyl ester (PC61BM) doped with the small molecule 4,7-diphenyl-1,10-phenanthroline (Bphen), to enhance the electron mobility, and a hole transfer layer (HTL) comprising poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) doped with molybdenum disulfide (MoS2) nanosheets, to enhance the hole mobility. We used ultraviolet photoelectron spectroscopy to determine the energy levels of these composite ETLs and HTLs; atomic force microscopy and scanning electron microscopy to probe their surface structures; and transmission electron microscopy and synchrotron grazing-incidence small-angle X-ray scattering to decipher the structures of the ETLs. Adding a small amount (less than 1%) of Bphen allowed us to tune the energy levels of the ETL and decrease the size of the PC61BM clusters and, therefore, generate more PC61BM aggregation domains to provide more pathways for electron transport, leading to enhanced PCEs of the resulting perovskite devices. We used quantitative pump-probe data to resolve the carrier dynamics from the perovskite to the ETL and HTL, and observed a smaller possibility of carrier recombination and a shorter injection lifetime in the perovskite solar cell doubly modified with carrier transport layers, resulting in an enhancement of the PCE. The PCE reached 16% for a planar inverted perovskite device featuring an ETL incorporating 0.5 wt% Bphen within PC61BM and 0.1 wt% MoS2 within PEDOT:PSS; this PCE is more than 50% higher than the value of 10.2% for the corresponding control device.
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.
Evolving molecular architectures of donor-acceptor conjugated polymers for photovoltaic applications: from one-dimensional to branched to two-dimensional structures
(2017-12-14)
Su, Yu-Wei
;
Lin, Yu-Che
;
Wei, Kung-Hwa
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Over the last ten years, the molecular architectures of p-type donor-acceptor (D-A) conjugated polymers designed for bulk heterojunction (BHJ) photovoltaics, when mixed with fullerenes or n-type polymers, have progressed substantially from one-dimensional (1-D) to branched to two-dimensional (2-D) D-A conjugated structures. In the 1-D structures, alternating D and A units allow internal charge transfer along the conjugated backbone and increase the effective resonance length, as a result of facilitated pi-electron delocalization. Upon progressing from 1-D structures to branched D-A conjugated polymers (comprising repeating donor units in the main chain with electron-withdrawing side chain units) to 2-D conjugated polymers (having D-A repeating units on their backbones as well as perpendicular electron-donating groups on their D units), the solubility, effective conjugation length, and photophysical and BHJ photovoltaic properties have all been altered dramatically. The ideal p-type 2-D conjugated D-A polymer for use in BHJ photovoltaic devices should possess a low band gap (to broaden the absorption range), excellent packing characteristics (particularly along the out-of-plane direction, ensuring good carrier transport), and suitable energy levels for efficient electron transfer (to fullerene moieties or n-type polymers). In this review, we discuss the effects of the structural characteristics and optical properties of these conjugated polymers as well as their packing characteristics on the device performances.
Fabrication of high-performance, low-temperature solution processed amorphous indium oxide thin-film transistors using a volatile nitrate precursor
(2015-01-01)
Choi, Chang-Ho
;
Han, Seung-Yeol
;
Su, Yu-Wei
;
Fang, Zhen
;
Lin, Liang-Yu
In this study, we fabricate amorphous indium oxide thin film transistors (TFTs) on a display glass substrate at various annealing temperatures from 200 degrees C to 300 degrees C. Using a volatile nitrate precursor, we were able to fabricate TFTs with excellent device performance within this annealing temperature range. Amorphous In2O3 films could be obtained by carefully controlling the film thickness and annealing temperature. TFTs based on amorphous In2O3 channel layers with an average mobility as high as 7.5 cm(2) V-1 s(-1), an I-on/I-off ratio of 10(7), and V-on = -5 V could be fabricated at 300 degrees C annealing temperature in air. The devices prepared at 200 degrees C still exhibit transistor characteristics with an average mobility of 0.04 cm(2) V-1 s(-1), an Ion/Ioff ratio of 10(5), and V-on = 0 V. The temperature effects on the device performances are elucidated based on X-ray photoelectron spectroscopy and thermal gravimetric analysis characterization results of precursors and the resulting amorphous In2O3 thin films.
Fluorene Conjugated Polymer/Nickel Oxide Nanocomposite Hole Transport Layer Enhances the Efficiency of Organic Photovoltaic Devices
(2017-01-25)
Chiou, Guan-Chiun
;
Lin, Ming-Wei
;
Lai, Yu-Ling
;
Chang, Chiao-Kai
;
Jiang, Jian-Ming
A nanocomposite layer comprising the conjugated polymer poly[(9,9-bis(3\'(N,N-dimethylamino)propy1)-2,7-fluorene)-alt-2,7-(9,9-dioctyl)fluorene] (PFN) and nickel oxide (NiOx) has been employed as the hole transport layer (HTL) in organic photovoltaics (OPVs) featuring PBDTTBO-C-8 and [6,6] -phenyl -C-71-butyric acid methyl ester (PC71BM) as the active layer. The optimal device incorporating the PFN:NiOx nanocomposite as the HTLs displayed a power conversion efficiency (PCE) to 6.2%, up from 4.5% for the corresponding device incorporating pristine NiOx as the HTL layer: a nearly 40% improvement in PCE. X-ray photoelectron spectroscopy (XPS) was used to determine the types of chemical bonding, ultraviolet photoelectron spectroscopy (UPS) to measure the change in work function, and atomic force microscopy (AFM) to examine the morphology of the composite layers. The growth of nickel trioxide, Ni2O3, in the PFN:NiOx layer played a key role in producing the p-doping effect and in tuning the work function, thereby improving the overall device performance.
High-Efficiency Organic Tandem Solar Cells With Effective Transition Metal Chelates Interconnecting Layer
(2017-10-01)
Chang, Sheng-Yung
;
Lin, Yu-Che
;
Sun, Pengyu
;
Hsieh, Yao-Tsung
;
Meng, Lei
Organic tandem solar cells have two sub-cells vertically connected via a tunnel junction (or interconnecting layer, ICL), which the ICL plays a critical role of determining the performance of the tandem cell. In this manuscript, we report a new design of the ICL consisting of zirconium (IV) acetylacetonate (Zr-Acac) as the electron transport layer. The Zr-Acac has a suitable work function to pin the Fermi-level of the ICL and hence, can effectively behave as the charge recombination function for the tandem device. Comparing to the reference device consisting of ZnO ETL layer, the Zr-Acac ICL can effectively enhance the efficiency by 20%, from 8.4 to 10.1% power conversion efficiencies. More importantly, the Zr-Acac ETL layer functions effectively without thermal annealing, which not only simplifies the tandem solar cell processing, but also widens the front sub-cell material selection.
Linear solubilizing side chain substituents enhance the photovoltaic properties of two-dimensional conjugated benzodithiophene-based polymers
(2015-11-19)
Jiang, Jian-Ming
;
Raghunath, Putikam
;
Lin, Yu-Che
;
Lin, Hsi-Kuei
;
Ko, Chen-Lin
In this study we synthesized medium-band gap, two-dimensional (2-D) conjugated polymers comprising electron-rich benzo[1,2-b:4,5-b\'] dithiophene (BDT) units presenting conjugated thiophene (T) side chains and electron-deficient alkoxy-modified 2,1,3-benzooxadiazole (BO) moieties. We introduced various solubilizing substituents-linear alkyl, alkoxy, and alkythio units-on the thiophene side chains to obtain a series of 2-D conjugated D-pi-A polymers: PBDTT-C-BO, PBDTT-O-BO, and PBDTT-S-BO. The solubilizing substituents of the BDT units altered the solubility, conformations, and electronic properties of the synthesized conjugated polymers, allowing tuning of the photovoltaic properties when blended with fullerenes. We investigated the effects of the different linear solubilizing substituents of the BDT units on the structural, optical, and electronic properties (e.g., band gap energies) of the resulting 2-D conjugated polymers, as determined from quantum-chemical calculations, UV-Vis absorption spectra, and grazing-incidence X-ray diffraction. Atomic force microscopy and transmission electron microscopy images revealed the morphologies of active layers comprising these 2-D conjugated polymers and the fullerene derivative [6,6]-phenyl-C-71-butyric acid methyl ester (PC71BM). Through rational structural modifications of the solubilizing substituents in the 2-D conjugated polymers with alkoxy, alkythio or alkyl units, the resulting PCEs varied from 5.4 to 7.5%. A polymer solar cell based on a blend of PBDTT-C-BO and PC71BM exhibited the best photovoltaic performance among our three studied systems, with a high short-circuit current density (J(sc)) of 15.7 mA cm(-2) and a power conversion efficiency of 7.5%, without the need for any processing additives or post-treatment processes, highlighting the importance of careful selection of appropriate solubilizing substituent that attached to the donor segments when designing efficient D-pi-A polymers for use in solar cells. (C) 2015 Elsevier Ltd. All rights reserved.
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.
Nano-scale Morphology for Bulk Heterojunction Polymer Solar Cells
(2015)
Su, Yu-Wei
;
Chiu, Mao-Yuan
;
Wei, Kung-Hwa
;
材料科學與工程學系
;
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.
Organic photovoltaics
(2012-12-01)
Su, Yu-Wei
;
Lan, Shang-Che
;
Wei, Kung-Hwa
;
材料科學與工程學系
;
Department of Materials Science and Engineering
In the last ten years, the highest efficiency obtained from organic photovoltaics (OPVs), such as bulk heterojunction polymer: fullerene solar cells, has risen from 2.5 to 11 %. This rapid progress suggests that the commercialization of OPVs should be realized soon if we can solve some technical issues. The advances in the development of OPVs can be attributed to four fronts: (i) a better understanding of the mechanism of photon-to-electron conversion; (ii) new materials with tailored energy levels and solubility; (iii) new processing approaches to induce optimal microstructures in the active layer; and (iv) new device architectures with novel interfacial layers. Herein, we review the materials, the microstructures of the active layers, the device structures, the interfacial layers that have been developed recently for OPVs, and provide future perspectives for this promising technology.
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.
Structural Evolution of Crystalline Conjugated Polymer/Fullerene Domains from Solution to the Solid State in the Presence and Absence of an Additive
(2015-02-12)
Su, Yu-Wei
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Liu, Chih-Ming
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Jiang, Jian-Ming
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Tsao, Cheng-Si
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Cha, Hou-Chin
The power conversion efficiencies of polymer/fullerene solar cells are critically dependent on the nanometer-scale morphologies of their active layers, which are typically processed from solution. Using synchrotron wide- and small-angle X-ray scattering, we have elucidated the intricate mechanism of the structural transitions from solutions to solid films of the crystalline polymer poly[bis(dodecyl)thiophene-thieno[3,4-c]pyrrole-4,6-dione] (PBTTPD) and [6,6]-phenyl-C-71-butyric acid methyl ester (PC71BM), including the effect of the solvent additive 1,6-diiodohexane (DIH). We found that the local assembly of rigid-rod PBTTPD segments that formed in solution instantly and then relaxed within several hundred seconds upon cooling to room temperature from 90 degrees C could re-emerge and develop into seeds for subsequent crystallization of the polymer in the solid films. At room temperature (25 degrees C), the presence of DIH in chlorobenzene slightly enhanced the formation of local assembly PBTTPD segments in the supersaturated PBTTPD in PBTTPD/PC71BM blend solution. Two cases of films were subsequently developed from these blend solutions with drop-casted and spin-coated methods. For spin-coated thin films (90 nm thick), which evolve quickly, polymers crystallinity and the fullerene packing in the solid-state thin films were enhanced in the case of involving DIH. Regarding the effect of DIH for processing the drop-casted thick films (2.5 mu m thick), which evolve slowly, DIH has no observable effect on PBTTPD/PC71BM structure. Our results provide some understanding of the mechanism behind the structural development of polymer/fullerene blends upon their transitions from solution to the solid state, as well as the key functions of the additive.