| 1. |
- Liu, Wei, et al.
(författare)
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A-pi-A structured non-fullerene acceptors for stable organic solar cells with efficiency over 17%
- 2022
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Ingår i: Science in China Series B. - : SCIENCE PRESS. - 1674-7291 .- 1869-1870. ; 65:7, s. 1374-1382
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Tidskriftsartikel (refereegranskat)abstract
- With the development of photovoltaic materials, especially the small molecule acceptors (SMAs), organic solar cells (OSCs) have made breakthroughs in power conversion efficiencies (PCEs). However, the stability of high-performance OSCs remains a critical challenge for future technological applications. To tackle the inherent instability of SMA materials under the ambient conditions, much effort has been made to improve OSCs stability, including device modification and new materials design. Here we proposed a new electron acceptor design strategy and developed a "quasi-macromolecule" (QM) with an A-pi-A structure, where the functionalized pi-bridge is used as a linker between two SMAs (A), to improve the long-term stability without deteriorating device efficiencies. Such type of QMs enables excellent synthetic flexibility to modulate their optical/electro-chemical properties, crystallization and aggregation behaviors by changing the A and pi units. Moreover, QMs possess a unique long conjugated backbone combining high molecular weight over 3.5 kDa with high purity. Compared with the corresponding SMA BTP-4F-OD (Y6-OD), the devices based on newly synthesized A-pi-A type acceptors QM1 and QM2 could exhibit better device stability and more promising PCEs of 17.05% and 16.36%, respectively. This kind of "molecular-framework" (A-pi-A) structure provides a new design strategy for developing high-efficiency and -stability photovoltaic materials.
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| 2. |
- Liu, Wei, et al.
(författare)
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Manipulating molecular aggregation and crystalline behavior of A-DAD-A type acceptors by side chain engineering in organic solar cells
- 2022
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Ingår i: Aggregate. - : Wiley. - 2692-4560. ; 3:3
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Tidskriftsartikel (refereegranskat)abstract
- Alkyl chains engineering plays an important role in photovoltaic materials for organic solar cells. Herein, three A-DAD-A (acceptor-donor-acceptor-donor-acceptor) type acceptors named Y6, Y6-C4, and Y6-C5 with different branching position on the pyrrole motif are discussed and the relationship between molecular aggregation, crystalline, and device performance are systematically investigated. The distance between the branching position and the main backbone affects their optical absorption and energy levels. Y6-C4 and Y6-C5 with the branching position at the fourth and fifth carbon of the alkyl chain show blue-shifted absorption and increased electrochemical bandgaps, compared with Y6 with the branching position at the second carbon of the alkyl side chain. In addition, this distance influences the molecular aggregation and crystalline behavior of the donor/acceptor blends. Compared with Y6-C4, Y6-C5 possesses a stronger crystalline and aggregate ability in the blends with a lower non-radiative energy loss, which results in a higher open circuit voltage (V-oc) of 0.88 V. Finally, Y6-C5-based binary device achieved a high power conversion efficiency up to 16.73% with afill factor (FF) of 0.78. These results demonstrate that the side chain engineering is an effective strategy for tuning the molecular aggregation and crystalline to improve photovoltaic performance of the A-DAD-A type acceptors.
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| 3. |
- 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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| 4. |
- 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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