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- 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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| 2. |
- Song, Jiage, et al.
(författare)
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Over 13% Efficient Organic Solar Cells Based on Low-Cost Pentacyclic A-DA D-A-Type Nonfullerene Acceptor
- 2021
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Ingår i: Solar RRL. - : Wiley-Blackwell. - 2367-198X. ; 5:8
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Tidskriftsartikel (refereegranskat)abstract
- Recent studies have almost focused on finding active layer materials with extended pi-conjugation structures for high-performance organic solar cells (OSCs). However, with the extension of conjugate length, the synthesis difficulty and cost of materials will increase. Achieving high efficiency while reducing material costs is a prerequisite for the commercialization of OSCs. Herein, two low-cost A-DA D-A-type (where A and D represent an electron-withdrawing unit and an electron-donating unit, respectively) nonfullerene acceptors (Y25,Y26) are synthesized with pentacyclic fused backbone as the DA D electron-deficient core and 5,6-difluoro-3-(dicyandiamethyl) indigo as the end groups. Compared with classical Y series acceptors with heptacyclic backbone, although Y25 and Y26 own the reduced conjugated length, they still show moderate performance (11.65% and 13.34%), and the cost of synthesis is significantly reduced. Therefore, we provide a new molecular design idea for commercially efficient nonfullerene OSCs acceptors. We also find that adding alkyl chains to the beta site of thiophenes is beneficial to obtaining the reduced energetic disorder, dominant molecular stacking, and desirable morphology, which can facilitate charge carrier transport and prompt higher short-circuit current density (J(sc)) as well as fill factor.
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| 3. |
- Zhang, Chujun, et al.
(författare)
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A disorder-free conformation boosts phonon and charge transfer in an electron-deficient-core-based non-fullerene acceptor
- 2020
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Ingår i: Journal of Materials Chemistry A. - : ROYAL SOC CHEMISTRY. - 2050-7488 .- 2050-7496. ; 8:17, s. 8566-8574
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Tidskriftsartikel (refereegranskat)abstract
- Electron acceptors with a chemical structure of A-DA D-A (in which A denotes an acceptor moiety and D a donor moiety) are rapidly gaining prominence in organic solar cells (OSCs). In OSCs containing these acceptors, record power conversion efficiencies (PCEs) exceeding 16% are now widely reported. Despite encouraging advances related to new material designs and PCEs, the fundamental interplay between molecular structure and device performance still requires further understanding. Here, we choose two model A-DA D-A type acceptors, Y3 and Y18, that have almost identical structures, and examine how the presence of two extra alkyl chains (attached to the periphery of the DA D core) in Y18 impacts on its solid state properties and device performance. These properties include: (i) charge transport; (ii) heat transfer; and (iii) electronic disorder. We found that bulk-heterojunction (BHJ) OSCs that use Y3 and Y18 have markedly different PCEs of similar to 13 and 16%, respectively. Correspondingly, the BHJ containing Y18 possesses more efficient phonon transfer and charge transport and suppressed electronic disorder. Among these properties, the extremely low Urbach energy (E-U) of 23 meV in Y18 stands out because this is even below the thermal energy (similar to 26 meV), which sets the electronic disorder limit at room temperature. With all these contrasting results, a simple molecular model can be rationalized in which the extra alkyl chains in Y18 help to suppress the formation of rotamers, endowing it with a disorder free molecular conformation and remarkable solid state properties. This work provides not only a new physical understanding of the effect of alkyl chains in organic semiconductors, but also new ideas for the synthesis of novel materials that can be adopted for use in high-performance OSCs.
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