| 1. |
- Kristanl, Matej, et al.
(författare)
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The Seventh Visual Object Tracking VOT2019 Challenge Results
- 2019
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Ingår i: 2019 IEEE/CVF INTERNATIONAL CONFERENCE ON COMPUTER VISION WORKSHOPS (ICCVW). - : IEEE COMPUTER SOC. - 9781728150239 ; , s. 2206-2241
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Konferensbidrag (refereegranskat)abstract
- The Visual Object Tracking challenge VOT2019 is the seventh annual tracker benchmarking activity organized by the VOT initiative. Results of 81 trackers are presented; many are state-of-the-art trackers published at major computer vision conferences or in journals in the recent years. The evaluation included the standard VOT and other popular methodologies for short-term tracking analysis as well as the standard VOT methodology for long-term tracking analysis. The VOT2019 challenge was composed of five challenges focusing on different tracking domains: (i) VOT-ST2019 challenge focused on short-term tracking in RGB, (ii) VOT-RT2019 challenge focused on "real-time" short-term tracking in RGB, (iii) VOT-LT2019 focused on long-term tracking namely coping with target disappearance and reappearance. Two new challenges have been introduced: (iv) VOT-RGBT2019 challenge focused on short-term tracking in RGB and thermal imagery and (v) VOT-RGBD2019 challenge focused on long-term tracking in RGB and depth imagery. The VOT-ST2019, VOT-RT2019 and VOT-LT2019 datasets were refreshed while new datasets were introduced for VOT-RGBT2019 and VOT-RGBD2019. The VOT toolkit has been updated to support both standard short-term, long-term tracking and tracking with multi-channel imagery. Performance of the tested trackers typically by far exceeds standard baselines. The source code for most of the trackers is publicly available from the VOT page. The dataset, the evaluation kit and the results are publicly available at the challenge website(1).
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| 2. |
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| 3. |
- Yuan, Jun, et al.
(författare)
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Enabling low voltage losses and high photocurrent in fullerene-free organic photovoltaics
- 2019
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Ingår i: Nature Communications. - : NATURE PUBLISHING GROUP. - 2041-1723. ; 10
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Tidskriftsartikel (refereegranskat)abstract
- Despite significant development recently, improving the power conversion efficiency of organic photovoltaics (OPVs) is still an ongoing challenge to overcome. One of the prerequisites to achieving this goal is to enable efficient charge separation and small voltage losses at the same time. In this work, a facile synthetic strategy is reported, where optoelectronic properties are delicately tuned by the introduction of electron-deficient-core-based fused structure into non-fullerene acceptors. Both devices exhibited a low voltage loss of 0.57 V and high short-circuit current density of 22.0 mA cm(-2), resulting in high power conversion efficiencies of over 13.4%. These unconventional electron-deficient-core-based non-fullerene acceptors with near-infrared absorption lead to low non-radiative recombination losses in the resulting organic photovoltaics, contributing to a certified high power conversion efficiency of 12.6%.
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| 4. |
- Cheng, Hao-Wen, et al.
(författare)
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Realizing Efficient Charge/Energy Transfer and Charge Extraction in Fullerene-Free Organic Photovoltaics via a Versatile Third Component
- 2019
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Ingår i: Nano letters (Print). - : AMER CHEMICAL SOC. - 1530-6984 .- 1530-6992. ; 19:8, s. 5053-5061
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Tidskriftsartikel (refereegranskat)abstract
- Solution-processed organic photovoltaics (OPVs) based on bulk-heterojunctions have gained significant attention to alleviate the increasing demend of fossil fuel in the past two decades. OPVs combined of a wide bandgap polymer donor and a narrow bandgap nonfullerene acceptor show potential to achieve high performance. However, there are still two reasons to limit the OPVs performance. One, although this combination can expand from the ultraviolet to the near-infrared region, the overall external quantum efficiency of the device suffers low values. The other one is the low open-circuit voltage (V-OC) of devices resulting from the relatively downshifted lowest unoccupied molecular orbital (LUMO) of the narrow bandgap. Herein, the approach to select and incorporate a versatile third component into the active layer is reported. A third component with a bandgap larger than that of the acceptor, and absorption spectra and LUMO levels lying within that of the donor and acceptor, is demonstrated to be effective to conquer these issues. As a result, the power conversion efficiencies (PCEs) are enhanced by the elevated short-circuit current and V-OC; the champion PCEs are 11.1% and 13.1% for PTB7-Th:IEICO-4F based and PBDB-T:Y1 based solar cells, respectively.
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| 5. |
- Hu, Jinghua, et al.
(författare)
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Synthesis and First-principle Calculation of TiO2 Rutile Nanowire Electrodes for Dye-sensitized Solar Cells
- 2017
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Ingår i: International Journal of Electrochemical Science. - : Electrochemical Science Group. - 1452-3981. ; 12:10, s. 9725-9735
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, a TiO2 nanowire film synthesized via a hydrothermal method was prepared as a photoanode for dye-sensitized solar cells (DSSCs). The synthesized TiO2 nanowires were characterized by transmission electron microscopy and X-ray diffraction. The TiO2 nanowire film greatly improved the efficiency of the DSSC owing to the rapid interfacial electron transport in the one-dimensional TiO2 nanowires. The light absorption and interfacial electron transport, which play important roles in the efficiency of DSSCs, were investigated by UV-vis absorption spectroscopy and electrochemical impedance spectroscopy. The energy band structure and electron density of states of the rutile nanowire were calculated using a first-principles method and compared to bulk anatase and rutile TiO2 phases. The band gap of the rutile TiO2 nanowire was found to be less than that of anatase TiO2 by 0.6 eV. Further calculations using GGA+U yielded a similar band gap reduction. In addition to the redshift of the absorption edge originating from the smaller band gap, the larger surface area of the TiO2 nanowire compared to the bulk material is expected to facilitate the migration of photogenerated electrons and holes from inside to the surface of the material. This would result in a considerable improvement of the photocatalytic efficiency of TiO2.
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| 6. |
- Huang, Kun, et al.
(författare)
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Enhanced peak growth of global vegetation and its key mechanisms
- 2018
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Ingår i: Nature Ecology and Evolution. - : Springer Science and Business Media LLC. - 2397-334X. ; 2:12, s. 1897-1905
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Tidskriftsartikel (refereegranskat)abstract
- The annual peak growth of vegetation is critical in characterizing the capacity of terrestrial ecosystem productivity and shaping the seasonality of atmospheric CO2 concentrations. The recent greening of global lands suggests an increasing trend of terrestrial vegetation growth, but whether or not the peak growth has been globally enhanced still remains unclear. Here, we use two global datasets of gross primary productivity (GPP) and a satellite-derived Normalized Difference Vegetation Index (NDVI) to characterize recent changes in annual peak vegetation growth (that is, GPPmax and NDVImax). We demonstrate that the peak in the growth of global vegetation has been linearly increasing during the past three decades. About 65% of the NDVImax variation is evenly explained by expanding croplands (21%), rising CO2 (22%) and intensifying nitrogen deposition (22%). The contribution of expanding croplands to the peak growth trend is substantiated by measurements from eddy-flux towers, sun-induced chlorophyll fluorescence and a global database of plant traits, all of which demonstrate that croplands have a higher photosynthetic capacity than other vegetation types. The large contribution of CO2 is also supported by a meta-analysis of 466 manipulative experiments and 15 terrestrial biosphere models. Furthermore, we show that the contribution of GPPmax to the change in annual GPP is less in the tropics than in other regions. These multiple lines of evidence reveal an increasing trend in the peak growth of global vegetation. The findings highlight the important roles of agricultural intensification and atmospheric changes in reshaping the seasonality of global vegetation growth.
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| 7. |
- Luo, Zhenghui, et al.
(författare)
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Fine-Tuning Energy Levels via Asymmetric End Groups Enables Polymer Solar Cells with Efficiencies over 17%
- 2020
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Ingår i: Joule. - : CELL PRESS. - 2542-4351. ; 4:6, s. 1236-1247
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Tidskriftsartikel (refereegranskat)abstract
- Generally, it is important to fine-tune the energy levels of donor and acceptor materials in the field of polymer solar cell (PSCs) to achieve a minimal highest occupied molecular orbital (HOMO) energy offset, which yet is still sufficient for charge separation. Based on the high-performance small-molecule acceptor (SMA) of BTP-4F, we modified the end groups of BTP-4F from IC-2F to CPTCN-Cl. It was found that when both end groups were substituted by CPTCN-Cl, the energy level upshift was too large that caused unfavorable energetic alignment, thus poor device performance. By using the strategy of asymmetric end groups, we were able to achieve near optimal energy level match, resulting in higher open-circuit voltage (V-OC) and power conversion efficiency (PCE) compared with those given by the PM6:BTP-4F system. Our strategy can be useful and potentially applied to othermaterial systems for maximizing efficiency of non-fullerene PSCs.
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| 8. |
- Yuan, Jun, et al.
(författare)
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Understanding energetic disorder in electron-deficient-core-based non-fullerene solar cells
- 2020
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Ingår i: Science in China Series B. - : SCIENCE PRESS. - 1674-7291 .- 1869-1870. ; 63:8, s. 1159-1168
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Tidskriftsartikel (refereegranskat)abstract
- Recent advances in material design for organic solar cells (OSCs) are primarily focused on developing near-infrared non-fullerene acceptors, typically A-DA D-A type acceptors (where A abbreviates an electron-withdrawing moiety and D, an electron-donor moiety), to achieve high external quantum efficiency while maintaining low voltage loss. However, the charge transport is still constrained by unfavorable molecular conformations, resulting in high energetic disorder and limiting the device performance. Here, a facile design strategy is reported by introducing the "wing" (alkyl chains) at the terminal of the DA D central core of the A-DA D-A type acceptor to achieve a favorable and ordered molecular orientation and therefore facilitate charge carrier transport. Benefitting from the reduced disorder, the electron mobilities could be significantly enhanced for the "wing"-containing molecules. By carefully changing the length of alkyl chains, the mobility of acceptor has been tuned to match with that of donor, leading to a minimized charge imbalance factor and a high fill factor (FF). We further provide useful design strategies for highly efficient OSCs with high FF.
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| 9. |
- Zhu, Can, et al.
(författare)
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Tuning the electron-deficient core of a non-fullerene acceptor to achieve over 17% efficiency in a single-junction organic solar cell
- 2020
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Ingår i: Energy & Environmental Science. - : ROYAL SOC CHEMISTRY. - 1754-5692 .- 1754-5706. ; 13:8, s. 2459-2466
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Tidskriftsartikel (refereegranskat)abstract
- Finding effective molecular design strategies to enable efficient charge generation and small energy loss is among the long-standing challenges in developing high performance non-fullerene organic solar cells (OSCs). Recently, we reported Y-series non-fullerene acceptors with an electron-deficient-core-based fused structure (typically Y6), opening a new door to achieve high external quantum efficiency (∼80%) while maintaining low energy loss (∼0.57 eV). On this basis, further reducing the energy losses and ultimately improving the performance of OSCs has become a research hotspot. In this paper, we design and synthesize a new member of the Y-series acceptor family, Y18, which adopts a fused benzotriazole segment with unique luminescence properties as its electron-deficient core. Compared to Y6, the benzotriazole-based acceptor Y18 exhibits extended optical absorption and higher voltage. Consequently, the device delivers a promising power conversion efficiency of 16.52% with a very low energy loss of 0.53 eV. Further device optimization by exploiting a ternary blend strategy allowed us to achieve a high efficiency of 17.11% (certified as 16.76% by NREL). Y18 may become one of the most important candidate materials for its broader absorption spectra and higher voltage of Y18 (compared to Y6) in the OSCs field.
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