| 1. |
- Qin, Linqing, et al.
(författare)
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Triplet Acceptors with a D-A Structure and Twisted Conformation for Efficient Organic Solar Cells
- 2020
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Ingår i: Angewandte Chemie International Edition. - : WILEY-V C H VERLAG GMBH. - 1433-7851 .- 1521-3773. ; 59:35, s. 15043-15049
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Tidskriftsartikel (refereegranskat)abstract
- Triplet acceptors have been developed to construct high-performance organic solar cells (OSCs) as the long lifetime and diffusion range of triplet excitons may dissociate into free charges instead of net recombination when the energy levels of the lowest triplet state (T-1) are close to those of charge-transfer states ((CT)-C-3). The current triplet acceptors were designed by introducing heavy atoms to enhance the intersystem crossing, limiting their applications. Herein, two twisted acceptors without heavy atoms, analogues of Y6, constructed with large pi-conjugated core and D-A structure, were confirmed to be triplet materials, leading to high-performance OSCs. The mechanism of triplet excitons were investigated to show that the twisted and D-A structures result in large spin-orbit coupling (SOC) and small energy gap between the singlet and triplet states, and thus efficient intersystem crossing. Moreover, the energy level of T-1 is close to (CT)-C-3, facilitating the split of triplet exciton to free charges.
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| 2. |
- Zhang, Xin, et al.
(författare)
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Enhancing the Photovoltaic Performance of Triplet Acceptors Enabled by Side-Chain Engineering
- 2021
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Ingår i: Solar RRL. - : WILEY-V C H VERLAG GMBH. - 2367-198X. ; 5:10
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Tidskriftsartikel (refereegranskat)abstract
- Triplet excitons have both longer lifetimes and diffusion lengths than singlet excitons due to the nature of triplet excitons, which is expected to increase the photocurrent and further improve the performance of organic solar cells (OSCs). However, the working mechanism of triplet excitons in OSCs is not clearly clarified. Therefore, it is urgent to develop new triplet acceptors for in-depth understanding. Herein, a series of acceptors (BTn-4Cl) are synthesized by fine-tuning of the side-chain branch positions. The generation of triplet excitons of BTn-4Cl is confirmed by the time-resolved photoluminescence (TRPL) spectra, magnetophotocurrent (MPC) experiment, and electron paramagnetic resonance (EPR) spectra. The effects of side-chain engineering on the optoelectronic properties, packing behaviors, energy losses, charge transport properties, spin lifetimes of triplet polarons, and blend film morphologies are systematically studied. These results show that D18:BT3-4Cl-based OSCs possess the best power conversion efficiency (PCE) of 17.31% due to lower energy losses, less recombination losses, more balanced charge carrier mobilities, longer spin-lattice (T-1) relaxation time, and more favorable morphology. This work enhances the understanding of the structure-property relationship for high-performance triplet acceptors.
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| 3. |
- Zhang, Xin, et al.
(författare)
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High-Performance Noncovalently Fused-Ring Electron Acceptors for Organic Solar Cells Enabled by Noncovalent Intramolecular Interactions and End-Group Engineering
- 2021
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Ingår i: Angewandte Chemie International Edition. - : WILEY-V C H VERLAG GMBH. - 1433-7851 .- 1521-3773. ; 60:22, s. 12475-12481
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Tidskriftsartikel (refereegranskat)abstract
- Noncovalently fused-ring electron acceptors (NFREAs) have attracted much attention in recent years owing to their advantages of simple synthetic routes, high yields and low costs. However, the efficiencies of NFREAs based organic solar cells (OSCs) are still far behind those of fused-ring electron acceptors (FREAs). Herein, a series of NFREAs with S...O noncovalent intramolecular interactions were designed and synthesized with a two-step synthetic route. Upon introducing pi-extended end-groups into the backbones, the electronic properties, charge transport, film morphology, and energy loss were precisely tuned by fine-tuning the degree of multi-fluorination. As a result, a record PCE of 14.53 % in labs and a certified PCE of 13.8 % for NFREAs based devices were obtained. This contribution demonstrated that combining the strategies of noncovalent conformational locks and pi-extended end-group engineering is a simple and effective way to explore high-performance NFREAs.
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| 4. |
- Zhang, Xin, et al.
(författare)
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Side-Chain Engineering for Enhancing the Molecular Rigidity and Photovoltaic Performance of Noncovalently Fused-Ring Electron Acceptors
- 2021
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Ingår i: Angewandte Chemie International Edition. - : WILEY-V C H VERLAG GMBH. - 1433-7851 .- 1521-3773. ; 60:32, s. 17720-17725
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Tidskriftsartikel (refereegranskat)abstract
- Side-chain engineering is an effective strategy to regulate the solubility and packing behavior of organic materials. Recently, a unique strategy, so-called terminal side-chain (T-SC) engineering, has attracted much attention in the field of organic solar cells (OSCs), but there is a lack of deep understanding of the mechanism. Herein, a new noncovalently fused-ring electron acceptor (NFREA) containing two T-SCs (NoCA-5) was designed and synthesized. Introduction of T-SCs can enhance molecular rigidity and intermolecular pi-pi stacking, which is confirmed by the smaller Stokes shift value, lower reorganization free energy, and shorter pi-pi stacking distance in comparison to NoCA-1. Hence, the NoCA-5-based device exhibits a record power conversion efficiency (PCE) of 14.82 % in labs and a certified PCE of 14.5 %, resulting from a high electron mobility, a short charge-extraction time, a small Urbach energy (E-u), and a favorable phase separation.
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