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Alex K.-Y. Jen

Bio: Alex K.-Y. Jen is an academic researcher from City University of Hong Kong. The author has contributed to research in topics: Perovskite (structure) & Polymer solar cell. The author has an hindex of 128, co-authored 921 publications receiving 61811 citations. Previous affiliations of Alex K.-Y. Jen include University of Nebraska–Lincoln & Zhejiang California International NanoSystems Institute.


Papers
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Journal ArticleDOI
TL;DR: In this paper, a new strategy of supramolecular homodimerization to self-assemble EO dendritic films was demonstrated, in which two Dendritic units with semifluorinated dipolar 1,2,3-trifluorobenzene (TFB) moieties were attached to the donor end and the π-bridge center of push-pull tetraene chromophores.
Abstract: In organic electro-optic (EO) materials, strong dipole–dipole interactions hinder the highly efficient poling of nonlinear optical chromophores. Supramolecular self-assembly through π–π stacking of fluoroaromatics was proved to be one of the most effective strategies to simultaneously achieve high chromophore loading density and highly efficient poling. Herein, we demonstrated a new strategy of supramolecular homodimerization to self-assemble EO dendritic films, in which two dendritic units with semifluorinated dipolar 1,2,3-trifluorobenzene (TFB) moieties were attached to the donor end and the π-bridge centre of push–pull tetraene chromophores. In these new dendrimers, the use of monolithic and semifluorinated TFB rings to replace the heterodimers of phenyl and pentafluorophenyl moieties has greatly simplified the synthesis of dendrimers and their intermixing, and can further potentially enable more efficient and rapid intermixing of interacting moieties in the solid states than those in binary and ternary systems. Photophysical property analysis and DFT calculations were carried out to understand the macroscopic supramolecular self-assembly and microscopic polarizability of new TFB-based EO dendrimers. The poled films of these self-assembled dendritic EO films exhibited very large EO coefficients up to 248 pm V−1 at a wavelength of 1310 nm and excellent temporal stability at room temperature with a very minimal change of ∼5% for over 1000 hours. Our study therefore illustrates that homodimer stacking of TFB rings through dipole–dipole coupling provides stabilization energy similar to that of quadrupolar interaction of phenyl and pentafluorophenyl heterodimeric pairs. Due to the highly efficient poling and excellent temporal EO stability, TFB self-assembled EO dendrimers show great potential for application in photonic devices.

46 citations

Journal ArticleDOI
TL;DR: In this article, the authors used in situ thermally polymerized hole transporting materials containing triphenylamine/tetraphenyldiaminobiphenyl as side chains.
Abstract: We have fabricated highly efficient organic light-emitting diodes (LEDS) using in situ thermally polymerized hole transporting materials containing triphenylamine/tetraphenyldiaminobiphenyl as side chains. Double-layer LEDs made with these thermally polymerized polymers as the hole transporting layer and tris(8-hydroxyquinoline) aluminum as the emitting layer showed comparable brightness but lower turn-on voltages and better quantum efficiencies than the device made with the conventional hole transporting molecule, N-N′-diphenyl-N,N′-bis(3-methylphenyl)(1,1′-biphenyl)-4,4′-diamine.

46 citations

Journal ArticleDOI
TL;DR: In this paper, a configuration-locking strategy was developed for preparation of NLO chromophores with all the π-conjugated methine groups incorporated into plane-rigidified, fused, six-membered rings.
Abstract: A synthetic strategy has been developed for preparation of NLO chromophores with all the π-conjugated methine groups incorporated into plane-rigidified, fused, six-membered rings. The comparison of the rigidified chromophores to the analogous nonrigid chromophores shows that the configuration-locking methods provide a dramatic enhancement of molecular thermal stability. The data from UV−vis spectroscopy and X-ray crystallography reveal that the rigidity of the annulated rings does not diminish the planarity and the electron delocalization efficiency of the polyenic chain.

45 citations

Journal ArticleDOI
TL;DR: In this paper, the effects of binding ligand variation on the externally initiated Ni catalyzed polymerization of P3HT were investigated using a novel methodology allowing facile screening of ligands.
Abstract: The effects of binding ligand variation on the externally initiated Ni catalyzed polymerization of P3HT were investigated using a novel methodology allowing facile screening of ligands. P3HT was synthesized with >80% initiator incorporation for both mono- and bidentate phosphine ligands. Variation of the initiating aryl group demonstrated vastly superior results for o-tolyl over p-tolyl substituents.

45 citations


Cited by
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Journal ArticleDOI
18 Oct 2013-Science
TL;DR: In this article, transient absorption and photoluminescence-quenching measurements were performed to determine the electron-hole diffusion lengths, diffusion constants, and lifetimes in mixed halide and triiodide perovskite absorbers.
Abstract: Organic-inorganic perovskites have shown promise as high-performance absorbers in solar cells, first as a coating on a mesoporous metal oxide scaffold and more recently as a solid layer in planar heterojunction architectures. Here, we report transient absorption and photoluminescence-quenching measurements to determine the electron-hole diffusion lengths, diffusion constants, and lifetimes in mixed halide (CH3NH3PbI(3-x)Cl(x)) and triiodide (CH3NH3PbI3) perovskite absorbers. We found that the diffusion lengths are greater than 1 micrometer in the mixed halide perovskite, which is an order of magnitude greater than the absorption depth. In contrast, the triiodide absorber has electron-hole diffusion lengths of ~100 nanometers. These results justify the high efficiency of planar heterojunction perovskite solar cells and identify a critical parameter to optimize for future perovskite absorber development.

8,199 citations

Journal Article
TL;DR: In this paper, transient absorption and photoluminescence-quenching measurements were performed to determine the electron-hole diffusion lengths, diffusion constants, and lifetimes in mixed halide and triiodide perovskite absorbers.
Abstract: Organic-inorganic perovskites have shown promise as high-performance absorbers in solar cells, first as a coating on a mesoporous metal oxide scaffold and more recently as a solid layer in planar heterojunction architectures. Here, we report transient absorption and photoluminescence-quenching measurements to determine the electron-hole diffusion lengths, diffusion constants, and lifetimes in mixed halide (CH3NH3PbI(3-x)Cl(x)) and triiodide (CH3NH3PbI3) perovskite absorbers. We found that the diffusion lengths are greater than 1 micrometer in the mixed halide perovskite, which is an order of magnitude greater than the absorption depth. In contrast, the triiodide absorber has electron-hole diffusion lengths of ~100 nanometers. These results justify the high efficiency of planar heterojunction perovskite solar cells and identify a critical parameter to optimize for future perovskite absorber development.

6,454 citations

Journal ArticleDOI
01 Aug 2014-Science
TL;DR: Perovskite films received a boost in photovoltaic efficiency through controlled formation of charge-generating films and improved current transfer to the electrodes and low-temperature processing steps allowed the use of materials that draw current out of the perovskites layer more efficiently.
Abstract: Advancing perovskite solar cell technologies toward their theoretical power conversion efficiency (PCE) requires delicate control over the carrier dynamics throughout the entire device. By controlling the formation of the perovskite layer and careful choices of other materials, we suppressed carrier recombination in the absorber, facilitated carrier injection into the carrier transport layers, and maintained good carrier extraction at the electrodes. When measured via reverse bias scan, cell PCE is typically boosted to 16.6% on average, with the highest efficiency of ~19.3% in a planar geometry without antireflective coating. The fabrication of our perovskite solar cells was conducted in air and from solution at low temperatures, which should simplify manufacturing of large-area perovskite devices that are inexpensive and perform at high levels.

5,789 citations

Journal ArticleDOI
TL;DR: This paper presents a meta-analysis of the chiral stationary phase transition of Na6(CO3)(SO4)2, a major component of the response of the immune system to Na2CO3.
Abstract: Ju Mei,†,‡,∥ Nelson L. C. Leung,†,‡,∥ Ryan T. K. Kwok,†,‡ Jacky W. Y. Lam,†,‡ and Ben Zhong Tang*,†,‡,§ †HKUST-Shenzhen Research Institute, Hi-Tech Park, Nanshan, Shenzhen 518057, China ‡Department of Chemistry, HKUST Jockey Club Institute for Advanced Study, Institute of Molecular Functional Materials, Division of Biomedical Engineering, State Key Laboratory of Molecular Neuroscience, Division of Life Science, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China Guangdong Innovative Research Team, SCUT-HKUST Joint Research Laboratory, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640, China

5,658 citations

Journal ArticleDOI
12 Jun 2015-Science
TL;DR: An approach for depositing high-quality FAPbI3 films, involving FAP bI3 crystallization by the direct intramolecular exchange of dimethylsulfoxide (DMSO) molecules intercalated in PbI2 with formamidinium iodide is reported.
Abstract: The band gap of formamidinium lead iodide (FAPbI3) perovskites allows broader absorption of the solar spectrum relative to conventional methylammonium lead iodide (MAPbI3). Because the optoelectronic properties of perovskite films are closely related to film quality, deposition of dense and uniform films is crucial for fabricating high-performance perovskite solar cells (PSCs). We report an approach for depositing high-quality FAPbI3 films, involving FAPbI3 crystallization by the direct intramolecular exchange of dimethylsulfoxide (DMSO) molecules intercalated in PbI2 with formamidinium iodide. This process produces FAPbI3 films with (111)-preferred crystallographic orientation, large-grained dense microstructures, and flat surfaces without residual PbI2. Using films prepared by this technique, we fabricated FAPbI3-based PSCs with maximum power conversion efficiency greater than 20%.

5,458 citations