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Conformational Locking Control of 2D Outer Side Chains via Fluorine Atom Positioning for Improving the Thermal Stability of Organic Solar Cells
No full textAlongsidehigh power conversion efficiencies (PCEs), device stability,especially thermal issues, is another key factor for the successfulcommercialization of nonfullerene acceptor (NFA)-based organic solarcells (OSCs). Considering the significant effects of the side-chainengineering of NFAs on molecular packing and/or locking strongly associatedwith the thermal stability of OSCs, herein, we present two new isomericNFAs with 4-fluoro- and 2-fluoro-substituted hexylphenyl two-dimensional(2D) outer side chains (4FY and 2FY, respectively).In contrast with the 2FY having a horizontal stretchingconformation, 4FY exhibits a diagonal stretching conformationof the 2D outer side chains and a higher dipole moment, resultingin a huge difference in their crystalline/aggregation characteristics,i.e., 4FY possesses a higher crystallinity with a densermolecular packing than the 2FY neat film, as evidencedby thermal and morphological characterizations. Encouragingly, relativeto the one based on 2FY, the OSC based on 4FY delivers a PCE as high as 16.4%, together with excellent thermalstability (88.4% PCE retention under 85 & DEG;C for 360 h), whichis attributed to a more optimal and robust blend morphology inducedby its better compatibility into the used donor component and strongercrystallinity. This work demonstrates that in addition to the improvedphotovoltaic property, the appropriate F-positioning on the 2D outerside chains can play a key role in controlling their conformations,which can promote the increase of the thermal stability of OSCs
E-Feedback Delivered via a Social Q&A Platform as a Scaffolding Teaching Strategy in the English-Medium Instruction Context
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Utilization of Waste Lignin for Conversion to Carbon Supports and Nylon Precursors
No full textThe valorization of waste lignin for the production of high value-added chemicals is energetically and environmentally important. Here, a new catalytic process was developed to produce raw materials for nylon production utilizing 100% of the waste lignin emitted from industrial processes. Guaiacol, extracted from technical lignin, was converted to phenol through a hydrodeoxygenation reaction over carbon-supported MoO2 catalysts. The extracted lignin oil and the remaining solid residue were used as a carbon support to prepare supported catalysts. The produced phenol was selectively converted to cyclohexanone or cyclohexanol, over carbon-supported Pd catalysts. The produced cyclohexanone and cyclohexanol were further converted to caprolactam and adipic acid, the main reagents used to produce nylon-6 and nylon-6,6 fibers, respectively. This process was demonstrated using real kraft and Klason lignin released from industry. This study shed light to utilize waste lignin as a resource by producing not only guaiacol raw material for the production of high value-added nylon, but also the carbon support used for catalytic conversion
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No full textDepartment of Mechanical Engineeringclos
Autonomous landing of a UAV on a moving platform using image based visual servoing
No full textDepartment of Mechanical Engineeringclos
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No full textDepartment of Mechanical Engineeringclos
Investigation on the slump caused by the 2017 Pohang, South Korea, earthquake, and seismic fragility analyses for various earth slopes
No full textDepartment of Urban and Environmental Engineering (Disaster Management Engineering)clos
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No full textDepartment of Biomedical Engineeringclos
Trifluoromethyl Introduced Asymmetric Non-Fullerene Acceptors for Stable and Eco-Friendly Organic Solar Cells
Get PDFGraduate School of Semiconductor Materials and EngineeringOrganic solar cells (OSCs) are one of the most promising photovoltaic technologies due to their strong light absorption, low-cost device fabrication, solution processability, flexibility, and lightweight characteristics. The power conversion efficiency (PCE) of OSCs has significantly increased with the emergence of a non-fullerene acceptor (NFA) known as Y6 (IC2F-BEH-IC2F). Various chemical modifications of IC2F-BEH-IC2F have been made to adjust energy levels, resulting in a PCE of over 19%. Although there has been considerable progress in PCE research, further studies are needed to investigate the use of environmentally friendly solvents in device fabrication steps and develop devices with higher stability. In here, we report efficient OSCs based on halogen-free solvent-processable NFAs with trifluoromethyl group-introduced asymmetric IPC1CF3-BBO-IC2F and IPC1CF3-BBO-IC2Cl. The IPC1CF3 moiety, located at the end-group of the NFA, plays a significant role in lowering the highest occupied molecular orbital (HOMO) level of the NFA due to the strong electron-withdrawing ability of the trifluoromethyl. Additionally, the end-groups facilitate the downshift of the HOMO energy level in the order of IPC1CF3, IC2F, and IC2Cl. We also report a new polymer donor PM6-PBDBT55, which has upshifted HOMO level compared to the PM6. As a result, the large HOMO-HOMO level offset between the polymer donor and NFAs leads to a highly improved JSC. The NFAs??? processabilities are enhanced by extending the side alkyl chain in the pyrrole moiety of the NFA to 2-butyloctyl, which is longer than that of 2-ethylhexyl in IC2F-BEH-IC2F. We blended polymers with NFAs using o-xylene, a halogen-free solvent, to fabricate OSCs. Among them, PM6-PBDBT55:IPC1CF3-BBO-IC2F-based OSCs showed the highest PCE of 14.95%, a significant improvement compared to symmetric IPC1CF3-BBO-IPC1CF3-based OSCs. More importantly, OSCs based on asymmetric NFAs exhibited superior thermal stability and photostability to the PM6:Y6-based OSCs.clos