scispace - formally typeset
Search or ask a question
Author

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.


Papers
More filters
Journal ArticleDOI
TL;DR: In this article, the authors experimentally demonstrate electro-optic modulation in slotted photonic crystal waveguides based on silicon-on-insulator substrates covered and infiltrated with nonlinear optical polymers.
Abstract: Two dimensional photonic crystal waveguides in high index materials enable integrated optical devices with an extremely small geometrical footprint on the scale of micrometers. Slotted waveguides are based on the guiding of light in low refractive index materials and a field enhancement in this particular region of the device. In this letter we experimentally demonstrate electro-optic modulation in slotted photonic crystal waveguides based on silicon-on-insulator substrates covered and infiltrated with nonlinear optical polymers. A photonic crystal heterostructure is used to create a cavity, while simultaneously serving as an electrical connection from the slot to the metal electrodes that carry the modulation signal.

101 citations

Journal ArticleDOI
TL;DR: A series of bis(propylenedioxythiophene) (bis(ProDOT)) π-conjugated bridges bearing alkyl or aryl substituents in electro-optic (EO) chromophores is presented in this paper.
Abstract: Application of bis(propylenedioxythiophene) (bis(ProDOT)) π-conjugated bridges bearing alkyl or aryl substituents in electro-optic (EO) chromophores is presented. A series of three bis(ProDOT)-based chromophores and a bithiophene-based control chromophore were prepared and fully characterized with regard to EO applications. The highly planar bis(ProDOT) bridge results in slightly larger (∼10%) molecular hyperpolarizability (β) values as compared to the bithiophene bridge, as measured by hyper-Rayleigh scattering at a variety of wavelengths. In amorphous polycarbonate guest–host films, however, the bulky substituents on the bis(ProDOT) bridge result in significantly larger (∼70%) poling-induced EO coefficient (r33) values, as measured by simple reflection ellipsometry at 1310 nm. This can be attributed to a roughly 2-fold enhancement in poling efficiency due to reduced intermolecular dipole–dipole interactions. This chromophore architecture also exhibits excellent temporal alignment stability and photochem...

101 citations

Journal ArticleDOI
TL;DR: In this article, the use of a poled polymer as the terahertz sensor allows the identification of DAST phonons at 1.1, 3.0, 5.3, 8.5, and 12.5THz.
Abstract: Poled polymer films are employed in terahertz emission and detection using telecommunication wavelength femtosecond pulses. Films 10–15μm thick with electro-optic coefficients as high as 160pm∕V at 1300nm are used to generate and sense subpicosecond pulses with continuous bandwidth up to 15THz. Terahertz emission from a poled polymer film is compared to terahertz emission from the organic crystal DAST. The use of a poled polymer as the terahertz sensor allows the identification of DAST phonons at 1.1, 3.0, 5.3, 8.5, and 12.5THz.

101 citations

Journal ArticleDOI
TL;DR: In this paper, a multi-ring ladder-type low band-gap polymer (PIDTCPDT-DFBT) was developed to show enhanced light harvesting, charge transport, and photovoltaic performance.
Abstract: A multi-ring, ladder-type low band-gap polymer (PIDTCPDT-DFBT) is developed to show enhanced light harvesting, charge transport, and photovoltaic performance. It possesses excellent planarity and enhanced effective conjugation length compared to the previously reported fused-ring polymers. In order to understand the effect of extended fused-ring on the electronic and optical properties of this polymer, a partially fused polymer PIDTT-T-DFBT is also synthesized for comparison. The fully rigidified polymer provides lower reorganizational energy, resulting in one order higher hole mobility than the reference polymer. The device made from PIDTCPDT-DFBT also shows a quite promising power conversion efficiency of 6.46%. Its short-circuit current (14.59 mA cm−2) is also among the highest reported for ladder-type polymers. These results show that extending conjugation length in fused-ring ladder polymers is an effective way to reduce band-gap and improve charge transport for efficient photovoltaic devices.

101 citations

Journal ArticleDOI
TL;DR: A new type of benzobis(silolothiophene)-based low band gap copolymers PBSTBT and PBSTDTBT were developed via a facile synthetic method in high yield as discussed by the authors.
Abstract: A new type of benzobis(silolothiophene)-based low band gap copolymers PBSTBT and PBSTDTBT were developed via a facile synthetic method in high yield. The introduction of silicon atoms in the large fused rings provides new polymers with low HOMO levels and high hole mobilities up to 0.01 cm2 V−1 s−1. The results from preliminary characterization of bulk heterojuction solar cells showed PCE above 3.5% for both PBSTBT and PBSTDTBT.

101 citations


Cited by
More filters
Journal ArticleDOI
18 Oct 2013-Science
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

Journal ArticleDOI
01 Aug 2014-Science
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

Journal ArticleDOI
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

Journal ArticleDOI
12 Jun 2015-Science
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