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.

Organic light-emitting diodes containing fluorinated asymmetrical europium cored beta-diketone complexes

Abstract: Novel luminescent materials based on europium-cored complexes have been synthesized and incorporated intolight emitting diodes using poly (N-vinyl-carbazole) and poly (vinyl naphthalene) blends as doping hosts. Thecomplexes consists of fluorinated ! -diketone ligands chelated to europium. Excitation of the ligands and efficienttransfer of energy from the excited ligands to the metal core results in the emission of optically pure red light.The ligands were designed such that they include a polycyclic aromatic compound, phenanthrene, and a secondsubstituent to improve processibility. Phenanthrene is used to so that the ligand energy will match with the energy of themetal center. Partially fluorinated substituents were also used to help improve the efficiency and charge transfercapability of the resulting metal complex. The complex consisted of one equivalent of europium and three equivalentsof the ligand. One equivalent of either 1,10-phenanthroline or 4,7-diphenyl-1,10-phenanthroline was also chelated toenhance the stability of the complex.Double and triple layer devices were synthesized with the configuration of ITO/BTPD-PFCB/Europiumcomplex in a polymer blend/Ca/Ag for the double layer device and ITO/BTPD-PFCB/Europium complex in a polymerblend/PBD/Ca/Ag for the triple layer device. The double layer devices made with a polymer blend of PVNoutperformed the devices made from PVK as the emission bands of the PVN better match the absorption bands of theligands. A maximum brightness of 178 cd/m

Modification of a Teng-Man technique to measure both r33 and r13 electro-optic coefficients

Abstract: In this paper, we present a modified Teng-Man method to measure both electro-optic coefficients in a single measurement. Using our method, we confirm a linear dependence between the applied poling field and the measured electro-optic coefficients. The ratio between the two electro-optic coefficients is close to three, which is theoretically expected from a weakly oriented polymer film. Since conductive silicon is used as substrate, no auxiliary layers of transparent oxide or metal are required on the substrate, which simplifies both the sample preparation and the evaluation of the results.

A novel approach to achieve highly efficient nonlinear optical polymers from guest-host systems

Abstract: A series of side-chain electrooptic (E-O) polymers have been prepared by Diels-Alder reaction in a solid state and characterized for their nonlinear optical properties. A synthesized chromophore were easily attached to a pendent anthracenyl moiety functionalized on the poly(methylmethacrylate-co-anthrylmethylmethacrylate) thermally in the bulk films during the poling process without compromising E-O performances. We have also controlled a chromophore concentration to determine its critical loading density at which chromophore-chromophore electrostatic interaction occurs in the polymer matrix. The highest E-O coefficient was 110 pm/V for the 34 wt% of the doped chromophore in the polymer at the wavelength of 1.3 μm. A high loading density of chromophore was obtained without observing a severe phase separation in the polymer matrix by an AFM morphology study. This novel approach provides to demonstrate a strategy for developing highly efficient E-O materials with the full potential of a chromophore.

Electro-optic modulation in hybrid SOI and polymer slotted resonant photonic crystal heterostructures

Abstract: We present experimental evidence of electro-optic modulation in slotted photonic crystal heterostructure waveguides based on silicon-on-insulator substrates covered and infiltrated with nonlinear optical polymer material.

Electron-hole diffusion lengths exceeding 1 micrometer in an organometal trihalide perovskite absorber.

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.

Electron-Hole Diffusion Lengths Exceeding 1 Micrometer in an Organometal Trihalide Perovskite Absorber

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.

Interface engineering of highly efficient perovskite solar cells

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.

Aggregation-Induced Emission: Together We Shine, United We Soar!

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

High-performance photovoltaic perovskite layers fabricated through intramolecular exchange

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%.