Browsing by Author "Li, Jun"

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A theoretical search for stable bent and linear structures of low-lying electronic states of the titanium dioxide (TiO(2)) molecule
(2011-01-01)
Lin, Chih-Kai
;
Li, Jun
;
Tu, Zheyan
;
Li, Xiangyuan
;
Hayashi, Michitoshi
In this work geometric optimization and potential energy surface (PES) scan for the TiO(2) molecule were carried out to find out possible stable structures by using quantum chemical calculations. The ground state (S(0) 1 (1)A(1)) has the only equilibrium with a symmetric bent structure, whereas the linear conformer is unstable. The first singlet excited state (S(1) 1 (1)B(2)), on the other hand, possesses two potential minima where one is bent around the Franck-Condon region and the other is linear. The second singlet excited state (S(2) 1 (1)A(2)) has only one minimum which is linear, and at which geometry the first two excited states degenerate. Other low-lying singlet and triplet excited states have been investigated accordingly. Among the functionals applied in the present DFT calculations, B3LYP gave results most close to available experimental data, while some recently developed ones including HSE06, omega B97X-D and CAM-B3LYP were not satisfactory for this small system. Ab initio methods such as CASSCF, CASPT2 as well as CCSD-related calculations have been applied, and the latter two showed good results similar to DFT/B3LYP.
A theoretical search for stable bent and linear structures of low-lying electronic states of the titanium dioxide (TiO2) molecule
(2011-01-01)
Lin, Chih-Kai
;
Li, Jun
;
Tu, Zheyan
;
Li, Xiangyuan
;
Hayashi, Michitoshi
In this work geometric optimization and potential energy surface (PES) scan for the TiO2 molecule were carried out to find out possible stable structures by using quantum chemical calculations. The ground state (S-0 1 (1)A(1)) has the only equilibrium with a symmetric bent structure, whereas the linear conformer is unstable. The first singlet excited state (S-1 1 B-1(2)), on the other hand, possesses two potential minima where one is bent around the Franck-Condon region and the other is linear. The second singlet excited state (S-2 1 (1)A(2)) has only one minimum which is linear, and at which geometry the first two excited states degenerate. Other low-lying singlet and triplet excited states have been investigated accordingly. Among the functionals applied in the present DFT calculations, B3LYP gave results most close to available experimental data, while some recently developed ones including HSE06, omega B97X-D and CAM-B3LYP were not satisfactory for this small system. Ab initio methods such as CASSCF, CASPT2 as well as CCSD-related calculations have been applied, and the latter two showed good results similar to DFT/B3LYP.
Efficient, large area organic photovoltaic modules with active layers processed with non-halogenated solvents in air
(2017-04-01)
Lim, Siew-Lay
;
Ong, Kok-Haw
;
Li, Jun
;
Yang, Le
;
Chang, Yu-Fan
Organic photovoltaic (OPV) modules with excellent power conversion efficiencies of 4.20% and 5.87% were obtained with blends of novel low bandgap polymers, POD2T-DTBT and PDTBT-alt-1T, respectively, with PCBM as the active layers. Large area polymer:PCBM blend films were deposited by blade coating with high film uniformity, fast processing speed, and low material consumption, without the need for an inert atmosphere. With the requirements of future manufacturing in mind, the effects of air exposure on the active layers and the substitution of chlorinated solvents for polymer processing were investigated. While the decline of V-oc due to air exposure was recovered by appropriate treatment of the completed devices, FFand J(sc) were significantly affected due to interfacial effects, indicating that air exposure should be limited in duration. Active layers of POD2T-DTBT:PCBM processed with less toxic, non-halogenated mixed solvents, comprising non-polaro-xylene with small amounts of polar additive, showed a fine, interpenetrating nanofibrous network that facilitates charge transport in bulk heterojunction photovoltaic cells. The performance of POD2T-DTBT:PCBM photovoltaic cells and modules processed with the new ink formulations were on par with that obtained with chlorinated solvents, with the modules exhibiting impressive power conversion efficiencies above 4%. The results indicated that POD2T-DTBT was an outstanding candidate for future OPV production due to its high performance, processibility in different ink formulations and compatibility with the large area coating techniques. (C) 2017 Elsevier B.V. All rights reserved.
Infrared spectrum of the simplest Criegee intermediate CH2OO at resolution 0.25 cm(-1) and new assignments of bands 2 nu(9) and nu(5)
(2015-06-07)
Huang, Yu-Hsuan
;
Li, Jun
;
Guo, Hua
;
Lee, Yuan-Pern
;
應用化學系
The simplest Criegee intermediate CH2OO is important in atmospheric chemistry. It has been detected in the reaction of CH2I + O-2 with various spectral methods, including infrared spectroscopy; infrared absorption of CH2OO was recorded at resolution 1.0 cm(-1) in our laboratory. We have improved our system and recorded the infrared spectrum of CH2OO at resolution 0.25 cm(-1) with rotational structures partially resolved. Observed vibrational wavenumbers and relative intensities are improved from those of the previous report and agree well with those predicted with quantum-mechanical calculations using the MULTIMODE method on an accurate potential energy surface. Observed rotational structures also agree with the simulated spectra according to theoretical predictions. In addition to derivation of critical vibrational and rotational parameters of the vibrationally excited states to confirm the assignments, the spectrum with improved resolution provides new assignments for bands 2 nu(9) at 1234.2 cm(-1) and nu(5) at 1213.3 cm(-1); some hot bands and combination bands are also tentatively assigned. (C) 2015 AIP Publishing LLC.
Symmetry forbidden vibronic spectra and internal conversion in benzene
(2010)
Li, Jun
;
Lin, Chih-Kai
;
Li, Xiang Yuan
;
Zhu, Chao Yuan
;
Lin, Sheng Hsien
The spectra of symmetry-forbidden transitions and internal conversion were investigated in the present work. Temperature dependence was taken into account for the spectra simulation. The vibronic coupling, essential in the two processes, was calculated based on the Herzberg-Teller theory within the Born-Oppenheimer approximation. The approach was employed for the symmetry-forbidden absorption/fluorescence, and internal conversion between 1(1)A(1g) and 1(1)B(2u) states in benzene. Vibrational frequencies, normal coordinates, electronic transition dipole moments, and non-adiabatic coupling matrix elements were obtained by ab initio quantum chemical methods. The main peaks, along with the weak peaks, were in good agreement with the observed ones. The rate constant of the 1(1)A(1g) <- 1(1)B(2u) internal conversion was estimated within the order of 10(3) s(-1). This could be regarded as the lower limit (about 4.8 x 10(3) s(-1)) of the internal conversion. It is stressed that the distortion effect was taken into account both in the symmetry-forbidden absorption/fluorescence, and the rate constants of internal conversion in the present work. The distortion effects complicate the spectra and increase the rate constants of internal conversion.
Understanding Morphology Compatibility for High-Performance Ternary Organic Solar Cells
(2016-09-13)
Mai, Jiangquan
;
Lau, Tsz-Ki
;
Li, Jun
;
Peng, Shih-Hao
;
Hsu, Chain-Shu
Ternary organic solar cells are emerging as a promising strategy to enhance device power conversion efficiency by broadening the range of light absorption via the incorporation of additional light-absorbing components. However, how to find compatible materials that allow comparable loadings of each component remains a challenge. In this article, we focus on studying the donor polymer compatibilities in ternary systems from a morphological point of view. Four typical donor polymers with different chemical structures and absorption ranges were mutually combined to form six distinct ternary systems with fullerene derivative acceptors. Two compatible ternary systems were identified as showing significant improvements of efficiency from both binary control devices. Ternary morphologies were characterized by grazing incident X-ray scattering and correlated with device performance. We find that polymers that have strong lamellar interactions and relatively similar phase separation behaviors with the fullerene derivative are more likely to be compatible in ternary systems. This result provides guidance for polymer selection for future ternary organic solar cell research while relaxing the limitation of chemical structure similarity and greatly extends the donor candidate pool.