| 1. |
- Hu, Maowei, et al.
(författare)
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Efficient and Stable Dye-Sensitized Solar Cells Based on a Tetradentate Copper(II/I) Redox Mediator
- 2018
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 10:36, s. 30409-30416
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Tidskriftsartikel (refereegranskat)abstract
- The identification of an efficient and stable redox mediator is of paramount importance for commercialization of dye-sensitized solar cells (DSCs). Herein, we report a new class of copper complexes containing diamine-dipyridine tetradentate ligands (L1 = N,N'-dibenzyl-N,N'-bis-(pyridin-2-ylmethyl)ethylenediamine; L2 = N,N'-dibenzyl-N,N'-bis (6-methyl-pyridin-2-ylmethyl)ethylenediamine) as redox mediators in DSCs. Devices constructed with [Cu(L2)](2+/+) redox couple afford an impressive power conversion efficiency (PCE) of 9.2% measured under simulated one sun irradiation (100 mW cm(-2), AM 1.5G), which is among the top efficiencies reported thus far for DSCs with copper complex-based redox mediators. Remarkably, the excellent air, photo, and electrochemical stability of the [Cu(L2)](2+/+) complexes renders an outstanding long-term stability of the whole DSC device, maintaining similar to 90% of the initial efficiency over 500 h under continuous full sun irradiation. This work unfolds a new platform for developing highly efficient and stable redox mediators for large-scale application of DSCs.
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| 2. |
- Jiang, Xiaoqing, et al.
(författare)
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High-Performance Regular Perovskite Solar Cells Employing Low-Cost Poly(ethylenedioxythiophene) as a Hole-Transporting Material
- 2017
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Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 7
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Tidskriftsartikel (refereegranskat)abstract
- Herein, we successfully applied a facile in-situ solid-state synthesis of conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) as a HTM, directly on top of the perovskite layer, in conventional mesoscopic perovskite solar cells (PSCs) (n-i-p structure). The fabrication of the PEDOT film only involved a very simple in-situ solid-state polymerisation step from a monomer 2,5-dibromo-3,4-ethylenedioxythiophene (DBEDOT) made from a commercially available and cheap starting material. The ultraviolet photoelectron spectroscopy (UPS) demonstrated that the as-prepared PEDOT film possesses the highest occupied molecular orbital (HOMO) energy level of -5.5 eV, which facilitates an effective hole extraction from the perovskite absorber as confirmed by the photoluminescence measurements. Optimised PSC devices employing this polymeric HTM in combination with a low-cost vacuum-free carbon cathode (replacing the gold), show an excellent power conversion efficiency (PCE) of 17.0% measured at 100 mW cm(-2) illumination (AM 1.5G), with an open-circuit voltage (V-oc) of 1.05 V, a short-circuit current density (J(sc)) of 23.5 mA/cm(2) and a fill factor (FF) of 0.69, respectively. The present finding highlights the potential application of PEDOT made from solid-state polymerisation as a HTM for cost-effective and highly efficient PSCs.
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| 3. |
- Li, Xiaoxin, et al.
(författare)
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Enhanced S-2 Fluorescence from a Free-Base Tetraphenylporphyrin Surface-Mounted Metal Organic Framework
- 2018
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Ingår i: The Journal of Physical Chemistry C. - : AMER CHEMICAL SOC. - 1932-7447 .- 1932-7455. ; 122:41, s. 23321-23328
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Tidskriftsartikel (refereegranskat)abstract
- The ultrafast transient dynamics of a free-base tetraphenylporphyrin (H2TPP) surface-mounted metal organic framework (SURMOF) is spectroscopically characterized and compared with that of H2TPP in ethanol solution. A dramatic increase of the quantum yield of the Soret band fluorescence (S-2 -> S-0) is observed in the H2TPP-SURMOF, which is accompanied by an increase of the S-2 fluorescence lifetime and a broadening of the fluorescence spectra. In contrast, the Q band (S-1) fluorescence is strongly quenched in the H2TPP SURMOF compared with the fluorescence of H(2)TPPin ethanol solution. The observed transient absorption kinetics supports the fluorescence data. The enhanced fluorescence in the SURMOF compared with H2TPP in solution is attributed to the combination of two factors: the alignment of the vibrational energy levels of the dominant Franck-Condon active mode of the Soret and Q bands and the weaker coupling of these modes to the environment.
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| 4. |
- Li, Xiaoxin, et al.
(författare)
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Ultrafast Relaxation Dynamics in Zinc Tetraphenylporphyrin Surface-Mounted Metal Organic Framework
- 2018
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Ingår i: The Journal of Physical Chemistry C. - : AMER CHEMICAL SOC. - 1932-7447 .- 1932-7455. ; 122:1, s. 50-61
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Tidskriftsartikel (refereegranskat)abstract
- Ordered porphyrin-based metal organic frameworks (MOFs) may serve as a model for mimicking the natural photosynthesis with highly ordered chlorophylls, i.e., porphyrin-like chromophores. Study of light harvesting and energy transfer as the primary event of photosynthesis is of great importance leading to improvement of photovoltaics overall performance. Detailed characterization of ultrafast dynamics of zinc tetraphenylporphyrin (ZnTPP) surface mounted metal organic framework (SURMOF) is reported by using various steady-state and time-resolved laser spectroscopic techniques, i.e., time correlated single photon counting, fluorescence up-conversion and transient absorption pump-probe with 20 fs resolution. Obtained results in these nanoporous materials were compared with corresponding results for ZnTPP in ethanol measured under the same conditions. Dramatic quenching of both upper excited singlet state S-2 and first excited state SI was observed. Subpicosecond and picosecond lifetimes were detected in transient fluorescence and absorption. Analytical formulas are derived for the linear absorption, steady-state fluorescence, and fluorescence up-conversion signals. Theoretical description excellently reproduces experimental time and frequency resolved signals. Strong quenching of the femtosecond transients in SURMOF is explained in terms of highly efficient Forster resonance energy transfer between the neighboring porphyrin moieties which is caused by a strong spectral overlap of absorption and steady-state fluorescence spectra and quantum coherent energy transfer and redistribution.
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| 5. |
- Ni, Wenjun, et al.
(författare)
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Singlet Fission from Upper Excited Electronic States of Cofacial Perylene Dimer
- 2019
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Ingår i: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 10:10, s. 2428-2433
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Tidskriftsartikel (refereegranskat)abstract
- Singlet fission directly from the upper excited vibrational and electronic states of cofacial perylene dimers, bypassing the relaxed state S-1, was detected within 50 fs. This process competes well with vibrational cooling in S-1 (4.7-7.0 ps) and S-2 -> S-1 internal conversion (380 fs). The singlet fission has the energy threshold E = 3.06 eV. Other competitive relaxation processes are excimer and dimer cation formation on an ultrafast time scale. Excitation to higher energy levels (4.96 eV) leads to a higher efficiency of singlet fission.
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| 6. |
- Ni, Wenjun, et al.
(författare)
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Ultrafast spectroscopy reveals singlet fission, ionization and excimer formation in perylene film
- 2021
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Ingår i: Scientific Reports. - : Springer Nature. - 2045-2322. ; 11:1
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Tidskriftsartikel (refereegranskat)abstract
- Singlet exciton fission (SF) is a spin-allowed process whereby two triplet excitons are created from one singlet exciton. This phenomenon can offset UV photon energy losses and enhance the overall efficiency in photovoltaic devices. For this purpose, it requires photostable commercially available SF materials. Excited state dynamics in pure perylene film, ease of commercial production, is studied by time-resolved fluorescence and femtosecond transient absorption techniques under different photoexcitation energies. In film, polycrystalline regions contain perylene in H-type aggregate form. SF takes place from higher excited states of these aggregates in ultrafast time scale<30 fs, reaching a triplet formation quantum yield of 108%. Moreover, at (ex)=450 nm singlet fission was detected as a result of two-quantum absorption. Other competing relaxation channels are excimer (1 ps) and dimer radical cation formation (<30 fs). Excimer radiatively relaxes within 19 ns and radical cation recombines in 3.2 ns. Besides, exciton self-trapping by crystal lattice distortions occurs within hundreds of picosecond. Our results highlight potential of simple-fabricated perylene films with similar properties as high-cost single crystal in SF based photovoltaic applications.
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| 7. |
- Ni, Wenjun, et al.
(författare)
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Ultrafast Tuning of Various Photochemical Pathways in Perylene-TCNQ Charge-Transfer Crystals
- 2020
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 124:25, s. 13894-13901
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Tidskriftsartikel (refereegranskat)abstract
- Excited-state dynamics in a strong charge-transfer (perylene)(3)-7,7,8,8-tetracyanoquinodimethane (P3T1) single-crystal system was studied by use of femtosecond transient absorption and upconversion time-resolved fluorescence techniques. Charge separation within 0.6-1.2 ps and subsequent recombination within 6.6-12 ps was demonstrated. Moreover, the excited-state dynamics in the P3T1 crystal was found to depend on excitation energies. Excitation of upper excited electronic states (4.96 eV) leads to efficient direct population of perylene triplet states via singlet fission. At lower excitation photon energies, enhancement of triplet state formation via intersystem crossing as a result of efficient spin-orbit charge transfer was observed. By varying the excitation wavelength, the performance of optoelectronic devices can be tuned, i.e., photon absorption, free carrier transfer, mobility, and recombination.
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| 8. |
- Wu, Tong, et al.
(författare)
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Singlet fission from upper excited singlet states and polaron formation in rubrene film
- 2021
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Ingår i: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 11:8, s. 4639-4645
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Tidskriftsartikel (refereegranskat)abstract
- Femtosecond fluorescence up-conversion and transient absorption pump-probe setups are applied to study the relaxation dynamics of the lower and upper excited singlet electronic states in easy-to-make rubrene films. Upon 250 nm (4.96 eV) excitation, singlet fission was observed directly from S-2 state bypassing S-1 state within 30 fs i.e. breaking the classical Kasha rule. From the transient absorption measurements, polaron formation was also detected on the same time scale. Both singlet fission and polaron formation are accelerated from upper excited states compared with S-1 state. Our work shows that rubrene films with low degree of crystallinity could display efficient singlet fission, notably in the case of excitation to upper lying electronic states. This can strongly expand the applications of rubrene in organic electronics. Moreover, our results will provide a new direction for synthesizing novel materials with optimized excited state properties for organic photovoltaic applications.
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| 9. |
- Yu, Ze, et al.
(författare)
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High-efficiency perovskite solar cells employing a conjugated donor-acceptor co-polymer as a hole-transporting material
- 2017
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Ingår i: RSC Advances. - : ROYAL SOC CHEMISTRY. - 2046-2069. ; 7:44, s. 27189-27197
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Tidskriftsartikel (refereegranskat)abstract
- In this work, we have successfully introduced 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) as an efficient p-type dopant for donor-acceptor (D-A) co-polymer poly[2,6-(4,4-bis-(2ethylhexyl)- 4H-cyclopenta[2,1-b; 3,4-b'] dithiophene)-alt-4,7(2,1,3-benzothiadiazole)] (PCPDTBT) as an HTM in mesoscopic perovskite solar cells (PSCs). The bulk conductivity is significantly enhanced by 4 orders of magnitude when PCPDTBT is doped with F4TCNQ (6%, w/w). UV-vis and Fourier transform infrared spectroscopy (FTIR) results indicate the occurrence of p-doping, which results in higher bulk conductivity. The high conductivity leads to an impressive overall efficiency of 15.1%, which is considerably higher than the pristine PCPDTBT based devices (9.2%). The superior performance obtained should be largely attributed to the significant enhancement of the photocurrent density strongly correlated with a more efficient charge collection. This is the highest efficiency reported so far for PCPDTBT-based PSCs. Thus, molecularly p-doping has been demonstrated to be an effective strategy for further improving the performance of a wide range of D-A and other types of polymeric HTMs in PSCs.
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| 10. |
- Zhang, Li, et al.
(författare)
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13.6% Efficient Organic Dye-Sensitized Solar Cells by Minimizing Energy Losses of the Excited State
- 2019
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Ingår i: ACS Energy Letters. - : AMER CHEMICAL SOC. - 2380-8195. ; 4:4, s. 943-951
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Tidskriftsartikel (refereegranskat)abstract
- The electron-injection energy losses of dye-sensitized solar cells (DSSCs) are among the fundamental problems hindering their successful breakthrough application. Two triazatruxene (TAT)-based sensitizers, with one containing a flexible Z-type double bond and another a rigid single bond, coded as ZL001 and ZL003, respectively, have been synthesized and applied in DSSCs to probe the energy losses in the process of electron injection. Using time-resolved laser spectroscopic techniques in the kinetic study, ZL003 with the rigid single bond promotes much faster electron injection into the conductive band of TiO2 especially in the locally excited state (hot injection), which leads to higher electron density in TiO2 and a higher V-oc. The devices based on ZL003 exhibited a champion power conversion efficiency (PCE) of 13.6% with V-oc = 956 mV, J(sc) = 20.73 mA cm(-2), and FF = 68.5%, which are among the highest recorded results to date on single dye-sensitized DSSCs. An independent certified PCE of 12.4% has been obtained for devices based on ZL003.
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| 11. |
- Zhao, Tongyu, et al.
(författare)
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Revealing ultrafast relaxation dynamics in six-thiophene thin film and single crystal
- 2021
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Ingår i: Journal of Photochemistry and Photobiology A. - : Elsevier B.V.. - 1010-6030 .- 1873-2666. ; 404
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Tidskriftsartikel (refereegranskat)abstract
- The excited state dynamics of six-thiophene (6T) thin film and single crystal was studied by time-resolved fluorescence and femtosecond transient absorption techniques under different excitation conditions. The dominant process in 6T system is the generation of ion pairs, dissociated to polarons staying for up to 130−3700 ns in film and 1 ms in crystal. Singlet fission (SF) was directly observed from the upper vibrational levels of the first excited singlet state S1 in 6T thin film/single crystal within 30 fs, which competes with intramolecular vibrational relaxation. Triplet state lifetime is dramatically shortened from 6T single crystal (1 ms) to thin film (4 ns) due to triplet-triplet annihilation, which is influenced by structural defects in amorphous regions of 6T film. Compared with 6T crystal, the partially ordered semicrystalline morphology of 6T film suggests the impact of well-structured crystallinity and molecular packing on the photocarriers transport dynamics and lifetime of triplet state. Moreover, excitation to upper excited singlet state (4.96 eV) leads to a higher yield of polarons (factor of 4), while SF in film/crystal is fully suppressed. Existence of long-lived photogenerated polarons may count π-conjugated oligomers as promising materials for developing organic-molecule-based optoelectroinc devices.
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| 12. |
- Zhao, Tongyu, et al.
(författare)
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Singlet Fission, Polaron Formation, and Energy Transfer in Indolo[3,2-b]carbazole Thin Films and Single Crystals
- 2021
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 125:34, s. 18827-18833
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Tidskriftsartikel (refereegranskat)abstract
- The ultrafast excited-state relaxation dynamics of indolo[3,2-b]carbazole (ICZ) molecules were investigated in thin films and single crystals. In the ICZ film, singlet fission (SF) was directly observed both from the upper excited singlet states S-N within 480-850 fs and from the upper vibrational levels of the singlet state S-1 within 6-11 ps, which fully suppressed the intramolecular charge transfer (CT) process in S-1. In the ICZ crystal, the exciton relaxation through SF and polaron formation compete in the ultrafast timescale (<30 fs), which is accompanied by a thermally induced broadening of the S-1-S-N absorption band in the transient absorption spectra. The triplet-state lifetime is shortened from ICZ crystals (>1 ms) to films (2 mu s) due to SF with subsequent triplet-triplet annihilation, suggesting the impact of well-structured crystallinity and molecular packing on the exciton transport dynamics. The efficient SF together with well-characterized energy transfer and CT properties of ICZ solids extends the usage of ICZ-core-based organic materials in photovoltaic and electrochemical applications.
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| 13. |
- Zhou, Yichen, et al.
(författare)
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Upper Excited State Photophysics of Malachite Green in Solution and Films
- 2020
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Ingår i: Journal of Physical Chemistry B. - : AMER CHEMICAL SOC. - 1520-6106 .- 1520-5207. ; 124:21, s. 4293-4302
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Tidskriftsartikel (refereegranskat)abstract
- Relaxation pathways of upper excited electronic states of malachite green (MG) in ethanol and in films are studied by steadystate and time-resolved spectroscopic techniques. In contrast to ethanol, where MG emits weak short-lived spectrally well separated S-2 and S-1 fluorescence with the lifetimes similar to 0.3 and similar to 0.9 ps, MG films show a much stronger broadband fluorescence within 430-700 nm, revealing multiexponential kinetics with the characteristic decay times tau(1) approximate to 1 ps, tau(2) approximate to 10 ps, tau(3) approximate to 0.05-0.8 ns, and tau(4) approximate to 2-3 ns. By the analysis of spectroscopic responses of MG in ethanol and in films as well as by theoretical modeling, we demonstrate that significant increase of fluorescence lifetimes and substantial enhancement of fluorescence intensity in MG films are stipulated by the decrease of efficiency of the S-2 -> S-1 and S-1 -> S-0 internal conversion, which in turn is caused by hindrance of rotation of MG's phenyl rings controlling the S-2/S-1 and S-1/S-0 conical intersections. These findings indicate that MG films may become promising non-Kasha materials (with reasonable S-2 emission) with numerous photophysical and photochemical applications.
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| 14. |
- Zhu, Yong, et al.
(författare)
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Water oxidation by a noble metal-free photoanode modified with an organic dye and a molecular cobalt catalyst
- 2022
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 10:16, s. 9121-9128
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Tidskriftsartikel (refereegranskat)abstract
- A low-cost and easy-to-construct dye-sensitized photoanode for water oxidation was prepared by co-loading a new triphenylamine donor-acceptor organic chromophore (D1) and a Co4O4 cobalt cubane-based water oxidation catalyst (CoF) on TiO2 thin films. As the first example of a molecular catalyst-based, noble metal-free, dye-sensitized photoanode, the electrode, TiO2|D1,CoF, produces a higher photocurrent than other noble metal-free, dye-sensitized photoanodes with a relatively high faradaic efficiency for O2 production. The success of the dyad system lies in retarded interfacial charge recombination and extended light absorption both of which take advantage of the pyridine anchor-functionalized chromophore. In addition, the CoF catalyst, decorated with hydrophobic aliphatic chains, serves as a protective layer for stabilizing the organic dyes on electrode surfaces. Transient absorption measurement suggests the accumulation of oxidative equivalents on CoF by electron transfer on the TiO2 surface. The results and design principles presented here demonstrate the use of molecular engineering as a powerful tool for the exploration of low-cost solar water-splitting devices.
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