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, nonlinear optical chromophore coupled hybrid sol-gel materials have been synthesized and incorporated in Fabry-Perot etalon devices (EDs) using highly reflective distributed Bragg reflector mirrors.
Abstract: Nonlinear optical chromophore coupled hybrid sol-gel materials have been synthesized and incorporated in Fabry-Perot etalon devices (ED’s) using highly reflective distributed Bragg reflector mirrors. Etalon structures with indium tin oxide electrodes outside the ED cavity have been applied to reduce absorptive loss. Large tunability (∼0.75nm∕V), high finesse (∼235), and wide tunable range (>50nm) have been obtained. A transmitted light intensity isolation ratio of ∼35dB at ∼1550nm has been achieved at a low drive voltage of 10V. The electro-optic effect and inverse piezoelectric effect are discussed. The results indicate that such hybrid sol-gel ED’s are promising candidates for tunable filters in wavelength division multiplexing communication systems.
26 citations
TL;DR: The device derived from this hybrid ETL can maintain good ambient stability inherent from the pristine N2200 ETL, for which 60-70 % of initial PCE can be retained after being stored in air with 10-20 % humidity for 45 days.
Abstract: In this work, an efficient inverted perovskite solar cell with decent ambient stability is successfully demonstrated by employing an n-type polymer, poly{[N,N′-bis(2-octyldodecyl)-1,4,5,8-naphthalene diimide-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)} (N2200), as the electron-transporting layer (ETL). The device performance can be further enhanced from a power conversion efficiency (PCE) of 15 to 16.8 % by tailoring the electronic properties of N2200 with a polymeric additive, poly[9,9-bis(6′-(N,N-diethylamino)propyl)-fluorene-alt-9,9-bis(3-ethyl(oxetane-3-ethyloxy)-hexyl) fluorene] (PFN-Ox). More importantly, the device derived from this hybrid ETL can maintain good ambient stability inherent from the pristine N2200 ETL, for which 60–70 % of initial PCE can be retained after being stored in air with 10–20 % humidity for 45 days.
26 citations
TL;DR: A series of highly efficient, chemically and thermally stable (>310 °C) nonlinear optical chromophores were prepared through the replacement of the most reactive CN group in tricyanovinylthiophene derivatives with perfluoroaryl units.
26 citations
TL;DR: A facile room-temperature processed amine functionalized perylene-diimide (PDIN) can function as an efficient electron-transporting layer (ETL) to enhance the photovoltaic performance of inverted PDI-based non-fullerene solar cells as discussed by the authors.
Abstract: In this study, it is demonstrated that a facile room-temperature processed amine functionalized perylene-diimide (PDIN) can function as an efficient electron-transporting layer (ETL) to enhance the photovoltaic performance of inverted PDI-based non-fullerene solar cells. It is showed that the PDIN ETL possesses respectable mobilities and interfacial doping capability to the PDI-based acceptors to facilitate the charge transport and extraction in the devices. Moreover, it can modulate the morphological evolution of the bulk-heterojunction (BHJ) atop to result in a more crystalline, face-on orientation because of its improved compatibility to PDI-based acceptors. Consequently, the PDIN ETL enables the derived devices to have 10% higher power conversion efficiency (PCE) than the reference device. In addition, the PDIN can also be used as a surface modifier on ZnO to result in a ≈14% enhanced PCE than that of the pristine ZnO-based device. This study shows the feasibility of modulating the BHJ of non-fullerene organic photovoltaics by rationally selected ETLs to facilitate exciton dissociation and collection of the devices.
26 citations
TL;DR: In this paper, a thin sol-gel derived titanium dioxide (TiO2) barrier layer was added to the high electric field poling process to improve the temporal stability of poled electro-optic polymers.
Abstract: Significantly enhanced temporal stability of poled electro-optic (E-O) polymers could be achieved by inserting a thin sol–gel derived titanium dioxide (TiO2) barrier layer in the high electric field poling process. The resulting poled film can retain >90% of its original r33 value (169 pm V−1 at 1310 nm) after being annealed at 85 °C for 500 h. This is significantly higher (∼30%) compared to that obtained without the TiO2 layer. This barrier approach is also applicable to a variety of dielectric polymers although the degree of enhancement varies. The enhanced temporal stability of E-O polymers is attributed to reduced charge injection/accumulation that improves the stability of screening charges for poled films.
25 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