Author
Alex K.-Y. Jen
Other affiliations: University of Nebraska–Lincoln, Zhejiang California International NanoSystems Institute, University of Washington ...read more
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 published on a yearly basis
Papers
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TL;DR: In this article, high-efficiency polymer light-emitting diodes were fabricated by spin-coating a layer of neutral surfactant on top of the poly electroluminescent (EL) layer to facilitate the electron injection through the high-work-function aluminum cathode.
Abstract: High-efficiency polymer light-emitting diodes were fabricated by spin-coating a layer of neutral surfactant on top of the poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene] electroluminescent (EL) layer to facilitate the electron injection through the high-work-function aluminum cathode. The external luminous efficiency of the device can reach 3.59 cd/A, which is higher than the control device (1.89 cd/A) using calcium as cathode. It was found that when the combination of surfactant and aluminum was used as cathode the abundant hole-injection through a hole-transporting layer and hole pile-up at the inner side of the EL/surfactant interface causes an effective electric field to enhance electron injection.
87 citations
87 citations
TL;DR: The electro-optic coefficient of an organic nonlinear material exhibits a sharp resonance near the absorption maximum of the material due to this resonance, and the amplitude of the THz field generated from a 31-μm-thick EO polymer composite was observed to be larger than that emitted from a 1000-mthick crystal of ZnTe.
Abstract: The electro-optic (EO) coefficient of an organic nonlinear material exhibits a sharp resonance near the absorption maximum of the material Due to this resonance, we experimentally observe the amplitude of the THz field generated from a 31-μm-thick EO polymer composite to be larger than that emitted from a 1000-μm-thick crystal of ZnTe This comparison allows us to estimate the resonance enhanced EO coefficient of the polymer composite to be over 1250pm∕V at 800nm
86 citations
TL;DR: In this article, a triad of electron-withdrawing cyano groups and electron-rich moieties, triphenylamine (TPA) or tetraphenyldiaminobiphenyl (TPD), were synthesized by Knoevenagel condensation.
Abstract: New luminescent polymers that contain both electron-withdrawing cyano groups and electron-rich moieties, triphenylamine (TPA) or tetraphenyldiaminobiphenyl (TPD), were synthesized by Knoevenagel condensation of 1,4-bis(cyanomethyl)-2-[(2-ethylhexyl)oxy]-5-methoxybenzene with the dialdehyde of TPA or TPD, respectively. The polymers were characterized by NMR, FT-IR, microanalysis, GPC, DSC, and TGA. Efficient orange photoluminescence was observed with an absolute quantum efficiency of 48% for the TPA incorporated polymer (TPA-CNPPV). Cyclic voltammetry investigation showed that the polymers presented reversible oxidation and reduction with relatively low potentials, which suggested that the polymers have both good electron and hole injection abilities. We demonstrated an effective approach to synthesize polymers with the triad properties of efficient photoluminescence, good hole injection and high electron-affinity properties, which are highly desirable for application in light-emitting devices. This point ...
86 citations
TL;DR: This study establishes an effective architecture that can be generally applicable to all organic materials for improving their performance, and demonstrates an effective parallel tandem solar cell employing ultra-thin Ag as the intermediate anode.
Abstract: A high-performance parallel tandem solar cell employing ultra-thin Ag as the intermediate anode is demonstrated, which comprises a semitransparent front sub-cell and a microcavity assisted back sub-cell. In addition to the extended optical field as a result of the tandem architecture, the prominent microcavity resonance formed in the back sub-cell enables such a parallel tandem configuration to possess high light utilization efficiency (the peak EQE value is over 80%) and a high photovoltaic performance of 9.2%. This study establishes an effective architecture that can be generally applicable to all organic materials for improving their performance.
86 citations
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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
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
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
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