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.

Electron-Rich Alcohol-Soluble Neutral Conjugated Polymers as Highly Efficient Electron-Injecting Materials for Polymer Light-Emitting Diodes

Abstract: We report the design and synthesis of three alcohol-soluble neutral conjugated polymers, poly[9,9-bis(2-(2-(2-diethanolaminoethoxy) ethoxy)ethyl)fluorene] (PF-OH), poly[9,9-bis(2-(2-(2-diethanol-aminoethoxy)ethoxy)ethyl)fluorene-alt-4,4′-phenylether] (PFPE-OH) and poly[9,9-bis(2-(2-(2-diethanolaminoethoxy) ethoxy)ethyl)fluorene-alt-benzothiadizole] (PFBT-OH) with different conjugation length and electron affinity as highly efficient electron injecting and transporting materials for polymer light-emitting diodes (PLEDs). The unique solubility of these polymers in polar solvents renders them as good candidates for multilayer solution processed PLEDs. Both the fluorescent and phosphorescent PLEDs based on these polymers as electron injecting/transporting layer (ETL) were fabricated. It is interesting to find that electron-deficient polymer (PFBT-OH) shows very poor electron-injecting ability compared to polymers with electron-rich main chain (PF-OH and PFPE-OH). This phenomenon is quite different from that obtained from conventional electron-injecting materials. Moreover, when these polymers were used in the phosphorescent PLEDs, the performance of the devices is highly dependent on the processing conditions of these polymers. The devices with ETL processed from water/methanol mixed solvent showed much better device performance than the devices processed with methanol as solvent. It was found that the erosion of the phosphorescent emission layer could be greatly suppressed by using water/methanol mixed solvent for processing the polymer ETL. The electronic properties of the ETL could also be influenced by the processing conditions. This offers a new avenue to improve the performance of phosphorescent PLEDs through manipulating the processing conditions of these conjugated polymer ETLs.

Thermally Cross-Linkable Hole-Transporting Materials for Improving Hole Injection in Multilayer Blue-Emitting Phosphorescent Polymer Light-Emitting Diodes

Abstract: One of the most challenging tasks in fabricating multilayer polymer light-emitting diodes (PLEDs) is to develop robust hole-transporting materials that possess matched energy level with indium tin oxide (ITO) anode and the highest occupied molecular orbital (HOMO) of light-emitting polymers to facilitate efficient hole injection and transport. In this article, a series of thermally cross-linkable 4,4′,4′′-tris(N-carbazolyl)triphenylamine (TCTA) derivatives have been synthesized to explore their function as efficient hole-transporting materials for blue-emitting electrophorphorescent devices. In particular, their excellent solvent resistance enables them to be used in the double hole-transporting layer (HTL) device configuration to facilitate cascade hole injection. The effects of cross-linking temperature and the functional group on the compatibility between two HTLs are investigated through optical and atomic force microscopy. When vinylbenzyl ether is used as the cross-linking group for TCTA, it shows t...

Directed self-immobilization of alkaline phosphatase on micro-patterned substrates via genetically fused metal-binding peptide.

Abstract: Current biotechnological applications such as biosensors, protein arrays, and microchips require oriented immobilization of enzymes. The characteristics of recognition, self-assembly and ease of genetic manipulation make inorganic binding peptides an ideal molecular tool for site-specific enzyme immobilization. Herein, we demonstrate the utilization of gold binding peptide (GBP1) as a molecular linker genetically fused to alkaline phosphatase (AP) and immobilized on gold substrate. Multiple tandem repeats (n = 5, 6, 7, 9) of gold binding peptide were fused to N-terminus of AP (nGBP1-AP) and the enzymes were expressed in E. coli cells. The binding and enzymatic activities of the bi-functional fusion constructs were analyzed using quartz crystal microbalance spectroscopy and biochemical assays. Among the multiple-repeat constructs, 5GBP1-AP displayed the best bi-functional activity and, therefore, was chosen for self-immobilization studies. Adsorption and assembly properties of the fusion enzyme, 5GBP1-AP, were studied via surface plasmon resonance spectroscopy and atomic force microscopy. We demonstrated self-immobilization of the bi-functional enzyme on micro-patterned substrates where genetically linked 5GBP1-AP displayed higher enzymatic activity per area compared to that of AP. Our results demonstrate the promising use of inorganic binding peptides as site-specific molecular linkers for oriented enzyme immobilization with retained activity. Directed assembly of proteins on solids using genetically fused specific inorganic-binding peptides has a potential utility in a wide range of biosensing and bioconversion processes.

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%.