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
More filters
28 Aug 2011
TL;DR: In this article, the optical transmission for an optical input power of 30 mW at a wavelength of 1550 nm does not change for >1000 h. The authors also demonstrated high EO coefficient of >170pm/V at 1550nm in a short directional coupler switch.
Abstract: The optical transmission for an optical input power of 30 mW at a wavelength of 1550 nm does not change for >1000 h. We also demonstrated high EO coefficient of >170pm/V at 1550nm in a short directional coupler switch.
4 citations
4 citations
17 Aug 2010
TL;DR: In this article, a Mach-Zehnder interferometer is used to decouple the EO and piezoelectric tensor components for a poled polymer film.
Abstract: A Mach-Zehnder interferometer (MZI) is used to decouple the
electro-optic (EO) and piezoelectric tensor
components for a poled polymer film. In the past those using the MZI method failed to take into account the
piezoelectric contribution in the polymer which can lead to erroneous EO coefficient data. The typical poled sample of
polymer sandwiched between ITO glass and gold that was developed for the popular Teng-Man reflection ellipsometry
method is used, providing for easy comparison with that method. The sample serves as a mirror in one arm of the
interferometer with the gold side facing the beam for measuring the piezoelectric modulation and the glass side facing
the beam to measure the coupled piezoelectric and EO modulation. Optical biasing in the reference arm allows for the
baseline and modulated contrast of the system to be measured from which the tensor components are calculated. This
method has the advantage over the reflection ellipsometry method of allowing for the independent determination of the
Pockel's coefficients r13 and r33 and the piezoelectric coefficient d33. The r33 value of a guest host polymer that consists
of AJLZ53/amorphous polycarbonate (APC) was found to be 122.7 pm/V and 123.0 pm/V for the MZI and reflection
ellipsometry method respectively. The r33 data fits well to the dispersion of the second order susceptibility tensor
χ 333 (2)
based on the two-level model approximation. Measurements were done from 100 Hz to 100 kHz with the results
showing that at higher frequencies the mechanical effects in the sample are negligible and modulation is almost entirely
due to the EO effect, as expected.
4 citations
27 Oct 2003
TL;DR: In this paper, the state-of-the-art for high bandwidth, low voltage optical modulators for applications in fiber communication systems and in RF photonics is briefly reviewed.
Abstract: Material and fabrication advances have brought polymer high speed, low voltage EO modulators close to commercial development. The technology is now being applied to more complex photonic switches and circuits and we will review some of the latest applications of polymers in photonics. We will briefly review the state of the art for high band-width, low voltage optical modulators for applications in fiber communication systems and in RF photonics. Using an EO polymer, APC/CLD, we have demonstrated a waveguide Mach Zehnder modulator operating in a push-pull mode with low frequency V/sub /spl pi// of 1.2 V at 1300 nm and 1.8 V at 1550 nm. EO and passive polymers also hold promise in the field of micro-photonics. We will present our results on polymer micro-ring resonators integrated with polymer waveguides. Coupled micro-resonators can be used for wide-band tuning of lasers based on the vernier effect. These coupled resonators have been both voltage and thermally tuned. The measurements on a tunable laser based on the coupled resonators and EDFA that tunes over 35 nm will be presented.
4 citations
4 citations
Cited by
More filters
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