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: A series of anionic self-doped conjugated polyelectrolytes (CPEs) by copolymerization of a 1,4-bis(4-sulfonatobutoxy)benzene moiety with different counter monomers of thiophene, bithiophene and terthiophene is reported in this article.
Abstract: A series of anionic self-doped conjugated polyelectrolytes (CPEs) by copolymerization of a 1,4-bis(4-sulfonatobutoxy)benzene moiety with different counter monomers of thiophene, bithiophene, and terthiophene is reported. The CPEs show high conductivity of ≈10−4 S cm−1 due to being self-doped in a neutral state and exhibit excellent hole transporting property in the out-of-plane direction, compared with poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS). Moreover, the CPE incorporating a less electron-donating unit from terthiophene to thiophene exhibits a higher work function and therefore, PhNa-1T incorporating thiophene shows a relatively high work function of 5.21 eV than 4.97 eV of PEDOT:PSS. This can induce a higher internal field in the solar cell device, facilitating efficient charge collection to the electrode. As a result, polymer solar cell devices incorporating the CPEs as a hole transporting layer achieve enhanced photovoltaic performances from those of the conventional PEDOT:PSS-based devices. The solar cell efficiency reaches up to 9.89%, which is among the highest values demonstrated by PCE-10-based normal-type organic solar cells.
37 citations
TL;DR: The ability of nonlinear optical materials to transmit, process and store information forms the basis of emerging optoelectronic and photonic technologies as discussed by the authors, where organic chromophore-containing polymers, in which the refractive index can be controlled by light or an electric field, are expected to play an important role.
Abstract: The ability of nonlinear optical materials to transmit, process and store information forms the basis of emerging optoelectronic and photonic technologies. Organic chromophore-containing polymers, in which the refractive index can be controlled by light or an electric field, are expected to play an important role.
37 citations
TL;DR: In this paper, a C60-tethered 2,5-dithienylpyrrole triad was synthesized and the self-assembled monolayer (SAM) on a gold electrode was prepared.
Abstract: A C60-tethered 2,5-dithienylpyrrole triad was synthesized and the self-assembled monolayer (SAM) on a gold electrode was prepared. The three-electron reduced C60 radical anions of the triad in both solution and SAM film at room temperature were detected. The redox kinetics between the C60 moieties and the gold electrode is faster compared to that of the C60 SAMs with nonconjugated flexible bridge/anchor systems, as determined by smaller peak splitting in the cyclic voltammogram. The photocurrent generated in a (Au/C60-triad/MV2+/Pt) cell upon irradiation of light is exceptionally large (3200 nA/cm2) with high quantum yield (51%). The electron-rich characteristics of the molecule and the rigid conjugated molecular framework stabilize the C60 radical anions generated during electrochemical reduction and lead to remarkable enhancement of photocurrent generation.
37 citations
TL;DR: This work shows that RB can alter how CH3NH3PbI3 contributes to the functional nature of devices and provides the first steps toward approaching functional perovskite interfaces in new ways for metrology and analysis of complex transient processes.
Abstract: In this study, reverse bias (RB)-induced abnormal hysteresis is investigated in perovskite solar cells (PVSCs) with nickel oxide (NiOx)/methylammonium lead iodide (CH3NH3PbI3) interfaces. Through comprehensive current–voltage (I–V) characterization and bias-dependent external quantum efficiency (EQE) measurements, we demonstrate that this phenomenon is caused by the interfacial ion accumulation intrinsic to CH3NH3PbI3. Subsequently, via systematic analysis we discover that the abnormal I–V behavior is remarkably similar to tunnel diode I–V characteristics and is due to the formation of a transient tunnel junction at NiOx/CH3NH3PbI3 interfaces under RB. The detailed analysis navigating the complexities of I–V behavior in CH3NH3PbI3-based solar cells provided here ultimately illuminates possibilities in modulating ion motion and hysteresis via interfacial engineering in PVSCs. Furthermore, this work shows that RB can alter how CH3NH3PbI3 contributes to the functional nature of devices and provides the first...
37 citations
TL;DR: A detailed quantum-chemical investigation of donor-acceptor substituted dipolar nonlinear optical chromophores incorporating the 4-(dimethylamino)phenyl donor end group and a variety of strong heterocyclic acceptor end groups, including tricyanofurans andtricyanopyrroles.
Abstract: We report a detailed quantum-chemical investigation of donor-acceptor substituted dipolar nonlinear optical chromophores incorporating the 4-(dimethylamino)phenyl donor end group and a variety of strong heterocyclic acceptor end groups, including tricyanofurans and tricyanopyrroles. In particular, we study the variation of the molecular second-order polarizability (β) with the acceptor end group and when inserting auxiliary donors (thiophene) and acceptors (thiazole) into the π bridge. Both finite-field calculations (in the context of local contributions) and sum-over-states calculations were carried out in order to probe the relationship between β and the chemical structure of the various chromophores. The trends obtained with these two methods are fully consistent. The large β values (up to 700×10−30esu) as well as the observed tunability of the optical absorption maximum (λmax) make the chromophores investigated here interesting candidates for use in electro-optic applications at telecommunications wav...
37 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