Browsing by Author "Lai, Yun-Yu"

Now showing 1 - 3 of 3

A New Ladder-Type Germanium-Bridged Dithienocarbazole Arene and Its Donor-Acceptor Conjugated Copolymers: Synthesis, Molecular Properties, and photovoltaic Applications
(2014-11-11)
Jwo, Pei-Chi
;
Lai, Yu-Ying
;
Tsai, Che-En
;
Lai, Yun-Yu
;
Liang, Wei-Wei
We have developed a new germanium-bridged heptacyclic arene, dithienogermolocarbazole (DTGC), in which two outer thiophene subunits are covalently fastened to the central 2,7-carbazole core by two dibutylgermanium bridges. The germole moieties embedded in the DTGC structure were successfully constructed by one-pot nucleophilic cyclization in a high yield of 88%. Because of the relatively lower polarity of carbongermanium bonds, the DTGC unit is chemically stable under basic conditions, rendering its more versatile functionalization. Comparison of germanium-bridged DTGC with the carbon-bridged DTCC (dithienocyclopentacarbazole) and silicon-bridged DTSC (dithienosilolocarbazole) analogues reveals that the HOMO energy level of DTGC lies between those of DTCC and DTSC and so does the LUMO energy level of DTGC. Density functional theory (DFT) calculations suggest that DTSC and DTGC have more bent structures than DTCC, which plays an important role in determining their frontier orbital energies. The structural disparity could be amplified in their corresponding polymers. The DTGC unit was copolymerized with four different comonomers, including benzothiadiazole (BT), dithienylbenzothiadiazole (DTBT), difluorobenzothiadiazole (FBT), and dithienyldifluorobenzothiadiazole (DTFBT) to yield a series of new alternating donoracceptor copolymers, poly(dithienogermolo-carbazole-alt-benzothiadiazole) (PDTGCBT), poly(dithienogermolocarbazole-alt-dithienylbenzothiadiazole) (PDTGCDTBT), poly(dithienogermolocarbazole-alt-difluorobenzothiadiazole) (PDTGCFBT), and poly(dithienogermolocarbazole-alt-dithienyldifluorobenzothiadiazole) (PDTGCDTFBT). Because of the two additional thiophene rings in the repeating units on the backbone to facilitate pi-electron delocalization, PDTGCFDTBT showed a lower optical band gap than PDTGCFBT. Furthermore, PDTGCDTFBT also showed the lower-lying LUMO and HOMO energy levels than PDTGCDTBT as a result of the electron-withdrawing fluorine atoms. Consequently, the bulk heterojunction solar cell incorporating PDTGCDTFBT delivered the highest performance with V-oc of 0.84 V, Jsc of 9.87 mA/cm(2), FF of 48.8%, and PCE of 4.05%. By adding 3 vol % 1-chloronaphthalene to tailor the morphology, the solar cell using PDTGCDTFBT with higher molecular weight exhibited the improved efficiency of 4.50% with a V-oc of 0.84 V, a J(sc) of 11.19 mA/cm(2), and an FF of 47.7%.
Angular-Shaped 4,10-Dialkylanthradiselenophene and Its Donor-Acceptor Conjugated Polymers: Synthesis, Physical, Transistor, and Photovoltaic Properties
(2015-10-13)
Lai, Yu-Ying
;
Chang, Huan-Hsuan
;
Lai, Yun-Yu
;
Liang, Wei-Wei
;
Tsai, Che-En
An angular-shaped and isomerically pure 4,10-di(2-octyl)dodecylanthradiselenophene (aADS) was successfully developed. The expedient synthesis to form the framework of aADS with two lateral side chains regioseleclively at its 4,10-positions is via a base-induced propargyl-allenyl isomerization/6 pi-electrocyclization/aromatization protocol. This pentacyclic distannylated aADS unit was then copolymerized with dithienyldiketopyrrolopyrrole (DPP) and dithienyl-5,6-difluoro-2,1,3-benzothiadiazole (DTFBT) acceptors with different alkyl side chains to afford four donor-acceptor copolymers: PaADSDPP, PaADSDTFBT-C-4, PaADSDTFBT-C-8, and PaADSDTFBT-C8C12. UV-vis spectroscopy and cyclic voltammetry revealed that PaADSDPP has the narrowest energy band gap, and PaADSDTFBT-C8C12 has larger band gap than PaADSDTFBT-C-4 and PaADSDTFBT-C-8. Two layer ONIOM (our own n-layered integrated molecular orbital and molecular mechanics) calculations were implemented to investigate the disparity in optical, electrochemical, and device properties between these polymers. Both experimental and theoretical data suggest that the aliphatic side chains play a significant role in determining the physical, transistor, and photovoltaic properties of the polymers. PaADSDTFBT-C-4 and PaADSDTFBT-C-8 exhibited organic-field-effect-transistor hole mobilities of 2.7 x 10(-2) and 1.0 x 10(-2) cm(2) V-1 s(-1), greatly outperforming that of PaADSDTFBT-C8C12 with a mobility of 5.4 X 10(-6) cm(2) V-1 s(-1). Polymer solar cells were fabricated on the basis of ITO/PEDOT:PSS/polymer:PC71BM/Ca/Al configuration. The efficiency decreased as the increase of bulkiness of the aliphatic side chains installed on DTFBT units (4.4% for PaADSDTFBT-C-4, 3.5% for PaADSDTFBT-C-8, 0.3% for PaADSDTFBT-C8C12). Atomic force microscopy images reveal that the degree of aggregation for the polymer:fullerene blends is influenced significantly by the bulkiness of aliphatic side chain installed on DTFBT. Noticeable aggregation was found for the PaADSDTFBT-C8C12:PC71BM blend. These results are in good agreement with the computational results elucidating that the intermolecular interactions between the polymers and PC71BM are sterically hindered by the bulky 2-octyldodecyl groups. This work not only presents a promising selenophene-based aADS building block but also provides insights into the side-chain engineering for donor-acceptor conjugated copolymers.
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.