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 paper, the effects of surface ligand exchange on the performance of hybrid organic/inorganic light emitting diodes (LEDs) that use colloidal nanocrystal quantum dots as emissive centers were examined.
Abstract: We examine the effects of surface ligand exchange on the performance of hybrid organic/inorganic light emitting diodes (LEDs) that use colloidal nanocrystal quantum dots as emissive centers. Using a series of primary alkylamines with different alkane chain lengths, we exchange the native surface ligands on a series of CdSe/CdZnS/ZnS core/shell/shell nanocrystal quantum dots and compare the differences in photoluminescence and electroluminescence efficiency of the emissive quantum dot layer. We fabricate LEDs made with octadecylamine-, octylamine-, and butylamine-exchanged quantum dots. We find that the differences in electroluminescence efficiency of the devices are not always proportional to the photoluminescence quantum efficiency of the quantum dots. We discuss this trend both in terms of the competing needs of high photoluminescence efficiency and good charge injection and energy transfer, and also in terms of the different processability and film morphology arising from the use of nanoparticles passivated with shorter ligands.
42 citations
TL;DR: In this article, high-speed polymer modulators were fabricated using low-Vpi AJL8 chromophore in amorphous polycarbonate, and highly calibrated frequency response measurements were obtained using convenient coplanar-microstrip transitions.
Abstract: High-speed polymer modulators were fabricated using low-Vpi AJL8 chromophore in amorphous polycarbonate, and highly calibrated frequency response measurements were obtained using convenient coplanar-microstrip transitions. These Mach-Zehnder modulators show good frequency response to 50 GHz, with a loss and velocity mismatch-limited Vpi at 50 GHz <12 V. The measurements establish AJL8 as an excellent candidate for future military analog optical links
42 citations
TL;DR: Based on the dithiolydinemethyl type donors and tricyanovinyl acceptor, a new series of highly efficient (βµ= 940 −2400 × 10 −48 esu) and thermally stable (275 −315 °C) nonlinear optical chromophores have been developed as discussed by the authors.
Abstract: Based on the ‘unconventional’ dithiolydinemethyl type donors and tricyanovinyl acceptor; a new series of highly efficient (βµ= 940–2400 × 10–48 esu) and thermally stable (275–315 °C) thiophene derived nonlinear optical chromophores have been developed.
42 citations
TL;DR: In this paper, lead-free cesium tin halide perovskite films with extremely smooth and uniform film morphology are obtained via vapor deposition, achieving a maximum EQE of 0.34% at 6.1'V.
Abstract: Lead‐free cesium tin halide perovskite films with extremely smooth and uniform film morphology are obtained via vapor deposition. All‐inorganic CsSnBr 3 perovskite light‐emitting diodes were achieved with a maximum EQE of 0.34% at 6.1 V. In addition, low‐threshold amplified spontaneous emission from optically pumped CsSnX 3 films, tunable by halogen substitution, is also demonstrated. These Sn‐based perovskite films with high film quality and high optical gain can also bear high current density up to 915 A cm −2 , enabling them to be considered as promising candidates for electrically pumped lasers.
42 citations
TL;DR: In this article, a review summarizes recent development of highly efficient organic electricoptic (OEO) materials and their applications in hybrid photonic devices, including EO polymer hybrid nanophotonic waveguides with high-index semiconductors, all polymer and polymer/sol-gel-based EO modulators using low-refractive-index cladding layers, and eO polymer-based electric field sensors.
Abstract: This review summarizes recent development of highly efficient organic electricoptic (OEO) materials and their applications in hybrid photonic devices. New generation of highly efficient EO polymers possessing large Pockels coefficients of 200-250 pm/V at 1.3 μm and excellent thermal and photochemical stability have been developed for advanced photonic devices. In addition, new pyroelectric poling process provides an efficient and reliable high field poling for EO polymers in multilayered thin films and nanophotonic waveguides. Using OEO materials as a key enabling element, significant progress has been made in the development of innovative hybrid EO devices, including EO polymer hybrid nanophotonic waveguides with high-index semiconductors, all polymer- and polymer/sol-gel-based EO modulators using low-refractive-index cladding layers, and EO polymer-based electric field sensors. At the end, this review also provides an outlook of future development of OEO materials and their hybrid systems for advanced photonic technologies.
42 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