Browsing by Author "Liao, Ming-Hung"

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Compact Bis-Adduct Fullerenes and Additive-Assisted Morphological Optimization for Efficient Organic Photovoltaics
(2014-11-26)
Lai, Yun-Yu
;
Liao, Ming-Hung
;
Chen, Yen-Ting
;
Cao, Fong-Yi
;
Hsu, Chain-Shu
Bis-adduct fullerenes surrounded by two insulating addends sterically attenuate intermolecular interaction and cause inferior electron transportation. In this research, we have designed and synthesized a new class of bis-adduct fullerene materials, methylphenylmethano-C-60 bis-adduct (MPC(60)BA), methylthienylmethano-C-60 bis-adduct (MTC(60)BA), methylphenylmethano-C-70 bis-adduct (MPC(70)BA), and methylthienylmethano-C-70 bis-adduct (MTC(70)BA), functionalized with two compact phenylmethylmethano and thienylmethylmethano addends via cyclopropyl linkages. These materials with much higher-lying lowest unoccupied molecular orbital (LUMO) energy levels successfully enhanced the V-oc values of the P3HT-based solar cell devices. The compact phenylmethylmethano and thienylmethylmethano addends to promote fullerene intermolecular interactions result in aggregation-induced phase separation as observed by the atomic force microscopy (AFM) and transmission electron microscopy (TEM) images of the poly(3-hexylthiophene-2,5-diyl) (P3HT)/bis-adduct fullerene thin films. The device based on the P3HT/MTC(60)BA blend yielded a V-oc of 0.72 V, a J(sc) of 5.87 mA/cm(2), and a fill factor (FF) of 65.3%, resulting in a power conversion efficiency (PCE) of 2.76%. The unfavorable morphologies can be optimized by introducing a solvent additive to fine-tune the intermolecular interactions. 1-Chloronaphthalene (CN) having better ability to dissolve the bis-adduct fullerenes can homogeneously disperse the fullerene materials into the P3HT matrix. Consequently, the aggregated fullerene domains can be alleviated to reach a favorable morphology. With the assistance of CN additive, the P3HT/MTC(60)BA-based device exhibited enhanced characteristics (a V-oc of 0.78 V, a J(sc) of 9.04 mA/cm(2), and an FF of 69.8%), yielding a much higher PCE of 4.92%. More importantly, the additive-assisted morphological optimization is consistently effective to all four compact bis-adduct fullerenes regardless of the methylphenylmethano or methylthienylmethano scaffolds as well as C-60 or C-70 core structures. Through the extrinsic additive treatment, these bis-adduct fullerene materials with compact architectures show promise for high-performance polymer solar cells.
Di(4-methylphenyl)methano-C(60) Bis-Adduct for Efficient and Stable Organic Photovoltaics with Enhanced Open-Circuit Voltage
(2011-09-13)
Cheng, Yen-Ju
;
Liao, Ming-Hung
;
Chang, Chih-Yu
;
Kao, Wei-Shun
;
Wu, Cheng-En
A new class of fullerene bis-adducts di(4-methyl-phenyl)methano-C(60) bis-adduct (DMPCBA), di(4-fluorophenyl)methano-C(60) bis-adduct (DFPCBA), and diphenylmethano-C(60) bis-adduct (DPCBA) were rationally designed and easily synthesized. Compared to the lowest unoccupied molecular orbital (LUMO) energy level of PC(61)BM (-3.95 eV), the double functionalization effectively raises the LUMO energy levels of these fullerene materials to ca. -3.85 eV, regardless of the substituent groups (CH(3)-, F-, and H-) at the para-position of the phenyl rings. This phenomenon suggests that the plane of the phenyl groups is preferentially parallel to the fullerene surface, leading to poor orbital interactions with C(60) and negligible electronic effect. Importantly, such geometry sterically protects and shields the core C(60) structure from severe intermolecular aggregation, rendering it intrinsically soluble, morphologically amorphous, and thermally stable. The device based on the P3HT:DMPCBA blend exhibited an open-circuit voltage (V(oc)) of 0.87 V, a short-circuit current density (J(sc)) of 9.05 mA/cm(2), and a fill factor (FF) of 65.5%, leading to a high power conversion efficiency (PCE) of 5.2%, which is superior to that of the P3HT:PC(61)BM-based device. Most significantly, the amorphous nature of DMPCBA effectively suppresses the thermal-driven aggregation and thus stabilizes the morphology of the P3HT:DMPCBA blend. Consequently, the device retained 80% of its original PCE value against thermal heating at 160 degrees C over 20 h.
Di(4-methylphenyl)methano-C-60 Bis-Adduct for Efficient and Stable Organic Photovoltaics with Enhanced Open-Circuit Voltage
(2011-09-13)
Cheng, Yen-Ju
;
Liao, Ming-Hung
;
Chang, Chih-Yu
;
Kao, Wei-Shun
;
Wu, Cheng-En
A new class of fullerene bis-adducts di(4-methyl-phenyl)methano-C-60 bis-adduct (DMPCBA), di(4-fluorophenyl)methano-C-60 bis-adduct (DFPCBA), and diphenylmethano-C-60 bis-adduct (DPCBA) were rationally designed and easily synthesized. Compared to the lowest unoccupied molecular orbital (LUMO) energy level of PC61BM (-3.95 eV), the double functionalization effectively raises the LUMO energy levels of these fullerene materials to ca. -3.85 eV, regardless of the substituent groups (CH3-, F-, and H-) at the para-position of the phenyl rings. This phenomenon suggests that the plane of the phenyl groups is preferentially parallel to the fullerene surface, leading to poor orbital interactions with C-60 and negligible electronic effect. Importantly, such geometry sterically protects and shields the core C-60 structure from severe intermolecular aggregation, rendering it intrinsically soluble, morphologically amorphous, and thermally stable. The device based on the P3HT:DMPCBA blend exhibited an open-circuit voltage (V-oc) of 0.87 V, a short-circuit current density (J(sc)) of 9.05 mA/cm(2), and a fill factor (FF) of 65.5%, leading to a high power conversion efficiency (PCE) of 5.2%, which is superior to that of the P3HT:PC61BM-based device. Most significantly, the amorphous nature of DMPCBA effectively suppresses the thermal-driven aggregation and thus stabilizes the morphology of the P3HT:DMPCBA blend. Consequently, the device retained 80% of its original PCE value against thermal heating at 160 degrees C over 20 h.
Diindenothieno[2,3-b]thiophene arene for efficient organic photovoltaics with an extra high open-circuit voltage of 1.14 ev
(2012)
Cheng, Yen-Ju
;
Cheng, Sheng-Wen
;
Chang, Chih-Yu
;
Kao, Wei-Shun
;
Liao, Ming-Hung
We report a novel diindenothieno[2,3-b]thiophene ladder-type hexacyclic arene for constructing a donor-acceptor copolymer PDITTDTBT. A device based on PDITTDTBT:PC71BM exhibited a high V-oc of 0.92 V with an impressive PCE of 5.8%, while a PDITTDTBT:DMPCBA-based device showed an extra high V-oc of 1.14 V.
Exciplex Electroluminescence Induced by Cross-Linked Hole-Transporting Materials for White Light Polymer Light-Emitting Diodes
(2011-08-09)
Cheng, Yen-Ju
;
Liao, Ming-Hung
;
Shih, Hung-Min
;
Shih, Ping-I
;
Hsu, Chain-Shu
A new class of cross-linkable N,N,N,N'-tetrapheny1-1,1'-biphenyl-4,4'-diame (TPD)-based hole-transporting materials (HTMs), DV-OMe-TPD, DV-Me-TPD, and DV-F-TPD, were designed and synthesized. Two vinyl groups in the TPD units are used for thermal cross-linking, whereas methoxy, methyl and fluoro groups are introduced to modulate the HOMO energy levels of the HTMs. These HTMs are thermally cross-linked to overcome interfacial mixing, realizing solution-processed polyfluorene (PFO)-based devices (ITO/cross-linked HTMs/PFO/CsF/ Al). Besides the characteristic blue emission of PFO, the devices exhibited a red emission whose energy is highly dependent on the HOMO energy of the cross-linked HTM used in the device. This result suggests that the red electroluminescence is derived from the exciplex generated by the adjacent hole and electron at the cross-linked HTM/fluorenone heterojunction interface. By doping small amount of 4,7-bis(9,9-dihexylfluoren-2-yl)-2,1,3-benzothiadiazole (BFBT) into the emissive layer (EML) to compensate green emission, the devices with the configuration of ITO/PEDOT:PSS/DV-Me-TPD/PFO doped with BEBT/CsF/Al exhibited white electroluminescence comprising three primary colors simultaneously. The 0.04 wt % doped device achieved a maximum luminous efficiency of 5.28 cd/A, which represents the highest efficiency for WPLEDs reported so far on the basis of the exciplex strategy. This device showed CIE chromaticity coordinates of (0.82, 0.42) which are close to the ideal white point (0.33, 0.33). We have demonstrated that integrating cross-linked triarylamine-based HTMs with fluorenone defects in PFO to induce exciplex electroluminescence can provide a useful way for realizing WPLED devices.
Morphological Stabilization by Supramolecular Perfl uorophenyl-C-60 Interactions Leading to Effi cient and Thermally Stable Organic Photovoltaics
(2014-03-01)
Liao, Ming-Hung
;
Tsai, Che-En
;
Lai, Yu-Ying
;
Cao, Fong-Yi
;
Wu, Jhong-Sian
A new PC61BM-based fullerene, [6,6]-phenyl-C-61 butyric acid pentafluorophenyl ester (PC61BPF) is designed and synthesized. This new n-type material can replace PC61BM to form a P3HT:PC61BPF binary blend or serve as an additive to form a P3HT:PC61BM:PC61BPF ternary blend. Supramolecular attraction between the pentafluorophenyl group of PC61BPF and the C-60 cores of PC61BPF/PC61BM can effectively suppress the PC61BPF/PC61BM materials from severe aggregation. By doping only 8.3 wt% PC61BPF, device PC(61)BP(F)651 exhibits a PCE of 3.88% and decreases slightly to 3.68% after heating for 25 h, preserving 95% of its original value. When PC61BP with non-fluorinated phenyl group is used to substitute PC61BPF, the stabilizing ability disappears completely. The efficiencies of PC(61)BP651 and PC(61)BP321 devices significantly decay to 0.44% and 0.11%, respectively, after 25 h isothermal heating. Most significantly, this strategy is demonstrated to be effective for a blend system incorporating a low band-gap polymer. By adding only 10 wt% PC61BPF, the PDTBCDTB:PC71BM-based device exhibits thermally stable morphology and device characteristics. These findings demonstrate that smart utilization of supramolecular interactions is an effective and practical strategy to control morphological evolution.
Reducing Regioisomers of Fullerene-Bisadducts by Tether-Directed Remote Functionalization: Investigation of Electronically and Sterically Isomeric Effects on Bulk-Heterojunction Solar Cells
(2014-01-22)
Liao, Ming-Hung
;
Lai, Yin-Yu
;
Lai, Yu-Ying
;
Chen, Yen-Ting
;
Tsai, Che-En
C-60 bis-adduct containing a mixture of regio-isomers with different LUMO energy levels and steric geometries could greatly affect the morphological and bulk properties. To investigate the regio-isomer effect on solar cell performance, we have successfully designed and synthesized a regio-selective 4-acetatephenyl-4'-methylphenylmethano C-60 bis-adduct (S-APM-CBA) by "tether-directed remote functionalization" strategy and a random 4-acetatephenyl-4'-methylphenylmethano C-60 bis-adduct denoted as R-APM-CBA by traditional cyclopropanation. The dramatic reduction in the number of regio-isomers in S-APM-CBA is confirmed by the H-1 NMR and HPLC measurements and theoretical calculation. Compared to the R-APM-CBA-based device with a J(sc) of 6.63 mA/cm(2), an FF of 44.3% and a PCE of 2.46%, the device using S-APM-CBA yielded a much lower J(sc) of 1.48 mA/cm(2), an FF of 32.2%, and a PCE of 0.38%. Consistently, the electron-only device using S-AMP-CBA exhibited lower electron mobility than the R-AMP-CBA-based device. These results imply that the electronic shallow-trap effect ascribed to the LUMO energy variations turned out to be insignificant in the AMP-CBA system. The lower efficiency and mobility of S-AMP-CBA might due to the assumption that the most probable trans-4-III isomer in S-AMP-CBA prevents the intermolecular facial contact of fullerenes, thereby hindering the electron transporting. Furthermore, the nanomorphology of S-AMP-CBA and R-AMP-CBA active layers could be different because of their different three-dimensional structures. This research demonstrated that steric effect of regio-isomers in a given C-60 bis-adduct is more crucial than electronic shallow-trap effect.
Triarylamine-based crosslinked hole-transporting material with an ionic dopant for high-performance PEDOT:PSS-free polymer solar cells
(2015-01-01)
Tsai, Che-En
;
Liao, Ming-Hung
;
Chen, Yung-Lung
;
Cheng, Sheng-Wen
;
Lai, Yu-Ying
A triarylamine-based material DVTPD containing two styryl groups has been developed. Upon isothermal heating at 180 degrees C for 30 min, DVTPD can be thermally cross-linked to form a solvent-resistant layer to realize the fabrication of solution-processed multilayer devices. The crosslinked DVTPD (denoted as X-DVTPD) layer possesses not only hole-collecting ability (HOMO = -5.3 eV) but also electron-blocking capability (LUMO = -2.2 eV). By incorporation of an ionic dopant, 4-isopropyl-4\'-methyldiphenyliodonium tetrakis(pentafluorophenylborate) (DPITPFB), into the X-DVTPD material (1 : 10 in wt%), a favourable morphology of the dopant/matrix layer was formed and the hole-mobility is significantly improved by three orders of magnitude compared to its non-doped state. This DPITPFB : X-DVTPD (1 : 10 in wt%) layer was employed as the hole-transporting layer to fabricate polymer solar cell devices (PSCs). The E-HOMO of the polymer in the active layer relative to the E-HOMO of the X-DVTPD (-5.3 eV) governs the hole transportation highly associated with the device performance. The higher-lying E-HOMO (-5.0 eV) of P3HT causes a large energy barrier for the hole transportation at the interface, leading to an unsatisfactory efficiency. The E-HOMO level of the PTB7 copolymer (-5.15 eV) is closer to -5.3 eV. As a result, the PTB7-based device can achieve 80% of the efficiency obtained from the corresponding PEDOT:PSS-based device. Furthermore, the PBDCPDTFBT copolymer has the same E-HOMO (-5.3 eV) with X-DVTPD. Consequently, the PBDCPDTFBT-based device showed a comparable efficiency of 5.3% to the corresponding PEDOT: PSS-based device. More importantly, PNDTDTFBT having the lowest-lying E-HOMO of -5.4 eV exhibits superior performance with a high PCE of 6.64%, outperforming its reference PEDOT: PSS-based device. This simple and useful hole-transporting system integrating the crosslinking and doping strategies to replace PEDOT:PSS can be widely used in solution-processed organic electronic devices.