| 1. |
- Ma, Ruijie, et al.
(författare)
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All-polymer solar cells with over 16% efficiency and enhanced stability enabled by compatible solvent and polymer additives
- 2022
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Ingår i: Aggregate. - : Wiley. - 2692-4560 .- 2766-8541. ; 3:3
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Tidskriftsartikel (refereegranskat)abstract
- Considering the robust and stable nature of the active layers, advancing the power conversion efficiency (PCE) has long been the priority for all-polymer solar cells (all-PSCs). Despite the recent surge of PCE, the photovoltaic parameters of the state-of-the-art all-PSC still lag those of the polymer:small molecule-based devices. To compete with the counterparts, judicious modulation of the morphology and thus the device electrical properties are needed. It is difficult to improve all the parameters concurrently for the all-PSCs with advanced efficiency, and one increase is typically accompanied by the drop of the other(s). In this work, with the aids of the solvent additive (1-chloronaphthalene) and the n-type polymer additive (N2200), we can fine-tune the morphology of the active layer and demonstrate a 16.04% efficient all-PSC based on the PM6:PY-IT active layer. The grazing incidence wide-angle X-ray scattering measurements show that the shape of the crystallites can be altered, and the reshaped crystallites lead to enhanced and more balanced charge transport, reduced recombination, and suppressed energy loss, which lead to concurrently improved and device efficiency and stability.
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| 2. |
- Sun, Huiliang, et al.
(författare)
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Reducing energy loss via tuning energy levels of polymer acceptors for efficient all-polymer solar cells
- 2020
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Ingår i: Science China Chemistry. - : Springer Science and Business Media LLC. - 1869-1870 .- 1674-7291. ; 63:12, s. 1785-1792
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Tidskriftsartikel (refereegranskat)abstract
- The open-circuit voltage (Voc) of all-polymer solar cells (all-PSCs) is typically lower than 0.9 V even for the most efficient ones. Large energy loss is the main reason for limiting Voc and efficiency of all-PSCs. Herein, through materials design using electron deficient building blocks based on bithiophene imides, the lowest unoccupied molecular orbital (LUMO) energy levels of polymer acceptors can be effectively tuned, which resulted in a reduced energy loss induced by charge generation and recombination loss due to the suppressed charge-transfer (CT) state absorption. Despite a negligible driving force, all-PSC based on the polymer donor and acceptor combination with well-aligned energy levels exhibited efficient charge transfer and achieved an external quantum efficiency over 10% while maintaining a large Voc of 1.02 V, leading to a 9.21% efficiency. Through various spectroscopy approaches, this work sheds light on the mechanism of energy loss in all-PSCs, which paves an avenue to achieving efficient all-PSCs with large Voc and drives the further development of all-PSCs.
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| 3. |
- Wang, Yuming, 1989-
(författare)
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Voltage Losses in Non-fullerene Organic Solar Cells
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Non-fullerene acceptors have significantly boosted the efficiencies of organic solar cells (OSCs) in the past few years. State-of-the-art OSCs have achieved a certificated power conversion efficiency of 17.4%. In spite of significant professes, there is still a gap between efficiencies of OSCs and those of traditional inorganic solar cells and emerging perovskite solar cells. One of the important reasons for this gap is the large voltage losses for OSCs. Understanding and reducing the voltage losses is of critical importance for further improving the performance of the OSCs. This thesis studies the voltage losses of OSCs based on non-fullerene acceptors.The charge transfer (CT) state plays a critical role in the open-circuit voltage (VOC) of the OSCs. According to the reciprocity relation between the electroluminescence (EL) and the external quantum efficiency of solar cells (EQEPV), we know that the sub-bandgap absorbance (responsible for large radiative recombination voltage losses) and the weak emission of CT states (responsible for large non-radiative voltage losses) are the reasons for large voltage losses in fullerene-based OSCs. In addition, the driving force, defined as the difference between the energy of the singlet states and CT states, was considered to be essential for efficient charge generation, especially when the OSC field was dominated by fullerene acceptors. A series of polymer: non-fullerene pairs with different driving forces were studied by spectroscopy methods e.g. Fourier-transfer photocurrent spectroscopy (FTPS) and electroluminescence spectroscopy. It was demonstrated that both radiative recombination voltage loss and the non-radiative energy loss can be suppressed by reducing driving forces, resulting in overall decreased voltage losses of the OSCs.Another question regarding the trade-off between the voltage losses and charge generation is still under debate – is the driving force essential for the efficient charge separation? A novel polymer: non-fullerene system with negligible offsets between both the lowest unoccupied molecular orbital (LUMO) and the highest unoccupied molecular orbital (HOMO) of the donor and acceptor was studied. Although the driving force for the new system is small, it works efficiently. It implies that efficient charge generation can occur with negligible driving forces for both electrons and holes, suggesting that the high VOC and efficient charge generation can be achieved at the same time for non-fullerene OSCs.In addition to binary OSCs, the voltage losses in ternary OSCs are also studied in this thesis. It was found that the VOC of the ternary organic solar cells cannot be well interpreted by the widely used alloy or parallel model. The non-radiative voltage loss, which is not paid much attention in the two models, was found to play an important role in the tunable VOC of the ternary OSCs. We demonstrate that the non-radiative voltage losses in ternary OSCs is dependent on the radiative recombination rates and the energy levels of the CT states of the two constituting binary OSCs. Furthermore, the aggregation of the individual components can be decreased by adding the third component, suppressing the aggregation caused quenching and leading to a reduced non-radiative recombination voltage loss.The non-fullerene based OSCs with small voltage losses show great potential for indoor applications. Although it might be difficult for OSCs to compete with commercial silicon solar cells for harvesting the solar energy, we demonstrate highly efficient and stable non-fullerene OSCs under indoor light, providing a unique application possibility where OSCs can out-compete other photovoltaic technologies. For the indoor application, the OSCs takes advantage of the easily tunable absorption range of the organic semiconductors, and avoids their drawbacks of the instability under strong outdoor light containing ultraviolet light.
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| 4. |
- Bai, Yang, et al.
(författare)
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Geometry design of tethered small-molecule acceptor enables highly stable and efficient polymer solar cells
- 2023
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Ingår i: Nature Communications. - : NATURE PORTFOLIO. - 2041-1723. ; 14:1
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Tidskriftsartikel (refereegranskat)abstract
- With the power conversion efficiency of binary polymer solar cells dramatically improved, the thermal stability of the small-molecule acceptors raised the main concerns on the device operating stability. Here, to address this issue, thiophene-dicarboxylate spacer tethered small-molecule acceptors are designed, and their molecular geometries are further regulated via the thiophene-core isomerism engineering, affording dimeric TDY-alpha with a 2, 5-substitution and TDY-beta with 3, 4-substitution on the core. It shows that TDY-alpha processes a higher glass transition temperature, better crystallinity relative to its individual small-molecule acceptor segment and isomeric counterpart of TDY-beta, and amore stablemorphology with the polymer donor. As a result, the TDY-alpha based device delivers a higher device efficiency of 18.1%, and most important, achieves an extrapolated lifetime of about 35000 hours that retaining 80% of their initial efficiency. Our result suggests that with proper geometry design, the tethered small-molecule acceptors can achieve both high device efficiency and operating stability.
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| 5. |
- Cheng, Li-Peng, et al.
(författare)
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Efficient CsPbBr3 Perovskite Light-Emitting Diodes Enabled by Synergetic Morphology Control
- 2019
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Ingår i: Advanced Optical Materials. - : WILEY-V C H VERLAG GMBH. - 2162-7568 .- 2195-1071. ; 7:4
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Tidskriftsartikel (refereegranskat)abstract
- The development of solution-processed inorganic metal halide perovskite light-emitting diodes (PeLEDs) is currently hindered by low emission efficiency due to morphological defects and severe non-radiative recombination in all-inorganic perovskite emitters. Herein, bright PeLEDs are demonstrated by synergetic morphology control over cesium lead bromide (CsPbBr3) perovskite films with the combination of two additives. The phenethylammonium bromide additive enables the formation of mixed-dimensional CsPbBr3 perovskites featuring the reduced grain size (amp;lt;15 nm) and efficient energy funneling, while the dielectric polyethyleneglycol additive promotes the formation of highly compact and pinhole-free perovskite films with defect passivation at grain boundaries. Consequently, green PeLEDs achieve a current efficiency of 37.14 cd A(-1) and an external quantum efficiency of 13.14% with the maximum brightness up to 45 990 cd m(-2) and high color purity. Furthermore, this method can be effectively extended to realize flexible PeLEDs on plastic substrates with a high efficiency of 31.0 cd A(-1).
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| 6. |
- Cui, Yong, et al.
(författare)
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Over 16% efficiency organic photovoltaic cells enabled by a chlorinated acceptor with increased open-circuit voltages
- 2019
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Ingår i: Nature Communications. - : NATURE PUBLISHING GROUP. - 2041-1723. ; 10
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Tidskriftsartikel (refereegranskat)abstract
- Broadening the optical absorption of organic photovoltaic (OPV) materials by enhancing the intramolecular push-pull effect is a general and effective method to improve the power conversion efficiencies of OPV cells. However, in terms of the electron acceptors, the most common molecular design strategy of halogenation usually results in down-shifted molecular energy levels, thereby leading to decreased open-circuit voltages in the devices. Herein, we report a chlorinated non-fullerene acceptor, which exhibits an extended optical absorption and meanwhile displays a higher voltage than its fluorinated counterpart in the devices. This unexpected phenomenon can be ascribed to the reduced non-radiative energy loss (0.206 eV). Due to the simultaneously improved short-circuit current density and open-circuit voltage, a high efficiency of 16.5% is achieved. This study demonstrates that finely tuning the OPV materials to reduce the bandgap-voltage offset has great potential for boosting the efficiency.
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| 7. |
- Fan, Baobing, et al.
(författare)
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Correlation of Local Isomerization Induced Lateral and Terminal Torsions with Performance and Stability of Organic Photovoltaics
- 2023
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Ingår i: Journal of the American Chemical Society. - : AMER CHEMICAL SOC. - 0002-7863 .- 1520-5126. ; 145:10, s. 5909-5919
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Tidskriftsartikel (refereegranskat)abstract
- Organic photovoltaics (OPVs) have achieved great progress in recent years due to delicately designed non-fullerene acceptors (NFAs). Compared with tailoring of the aromatic heterocycles on the NFA backbone, the incorporation of conjugated side-groups is a cost-effective way to improve the photoelectrical properties of NFAs. However, the modifications of side-groups also need to consider their effects on device stability since the molecular planarity changes induced by side-groups are related to the NFA aggregation and the evolution of the blend morphology under stresses. Herein, a new class of NFAs with localisomerized conjugated side-groups are developed and the impact of local isomerization on their geometries and device performance/stability are systematically investigated. The device based on one of the isomers with balanced side- and terminal-group torsion angles can deliver an impressive power conversion efficiency (PCE) of 18.5%, with a low energy loss (0.528 V) and an excellent photo- and thermal stability. A similar approach can also be applied to another polymer donor to achieve an even higher PCE of 18.8%, which is among the highest efficiencies obtained for binary OPVs. This work demonstrates the effectiveness of applying local isomerization to fine-tune the side-group steric effect and non-covalent interactions between side-group and backbone, therefore improving both photovoltaic performance and stability of fused ring NFA-based OPVs.
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| 8. |
- Fu, Huiting, et al.
(författare)
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Suppression of Recombination Energy Losses by Decreasing the Energetic Offsets in Perylene Diimide-Based Nonfullerene Organic Solar Cells
- 2018
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Ingår i: ACS Energy Letters. - : AMER CHEMICAL SOC. - 2380-8195. ; 3:11, s. 2729-2735
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Tidskriftsartikel (refereegranskat)abstract
- In this work, a range of nonfullerene organic solar cells comprising two perylene diimide (PDI)-based small molecule acceptors in combination with four representative polymer donors have been investigated and compared. In addition to significant differences in the power conversion efficiency, the energy losses of photovoltaic devices vary widely for these two PDI-based acceptors when paired with different donors. The sensitive Fourier-transform photocurrent spectroscopy (FTPS) and electroluminescence (EL) measurements have been performed to quantify their respective energetic offsets (Delta(Eoffiet)) and energy losses, with the aim of understanding the distinct energy losses in the studied organic blends. By comparing these results, we find that with decreasing Delta(Eoffset), recombination loss due to the charge-transfer state absorption A both nonradiative recombination loss and radiative are suppressed; as a result, the total energy loss is decreased. These observations offer a deep understanding of how the energetic offset affects the energy losses from the viewpoint of the Shockey-Queisser limit.
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| 9. |
- Giuri, Antonella, et al.
(författare)
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Ultra-Bright Near-Infrared Perovskite Light-Emitting Diodes with Reduced Efficiency Roll-off
- 2018
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Ingår i: Scientific Reports. - : NATURE PUBLISHING GROUP. - 2045-2322. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- Herein, an insulating biopolymer is exploited to guide the controlled formation of micro/nano-structure and physical confinement of alpha-delta mixed phase crystalline grains of formamidinium lead iodide (FAPbI(3)) perovskite, functioning as charge carrier concentrators and ensuring improved radiative recombination and photoluminescence quantum yield (PLQY). This composite material is used to build highly efficient near-infrared (NIR) FAPbI(3) Perovskite light-emitting diodes (PeLEDs) that exhibit a high radiance of 206.7 W/sr*m(2), among the highest reported for NIR-PeLEDs, obtained at a very high current density of 1000 mA/cm(2), while importantly avoiding the efficiency roll-off effect. In depth photophysical characterization allows to identify the possible role of the biopolymer in i) enhancing the radiative recombination coefficient, improving light extraction by reducing the refractive index, or ii) enhancing the effective optical absorption because of dielectric scattering at the polymer-perovskite interfaces. Our study reveals how the use of insulating matrixes for the growth of perovskites represents a step towards high power applications of PeLEDs.
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| 10. |
- Guo, Ruiqi, et al.
(författare)
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Double Active Layers Constructed with Halide Perovskite and Quantum Dots for Broadband Photodetection
- 2020
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Ingår i: Advanced Optical Materials. - : WILEY-V C H VERLAG GMBH. - 2162-7568 .- 2195-1071. ; 8:17
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Tidskriftsartikel (refereegranskat)abstract
- Herein, solution-processed, high-performance broadband (300-1100 nm) photodetectors based on double active layers incorporating narrow-bandgap CuInSe2 (CISe) quantum dots (QDs) and halide perovskite are devised. The CISe QDs/perovskite film as the photoactive layer boosts the photocurrent and suppresses dark current. Due to the joint light absorption effect of CISe QDs and halide perovskite, the photoelectric conversion capacity is improved. Furthermore, CISe QDs as an electron-blocking layer can effectively block electrons to the hole transport layer and reduce the thermal noise. The optimized photodetector exhibits responsivity over 150 mA W-1 in the visible and more than 20 mA W-1 in the near-infrared (800-1000 nm) ranges, specific detectivity of more than 7.0 x 10(12) Jones in the visible region and 7.7 x 10(11) Jones in the near-infrared region, a transient response time of 277 ns with the active area of 0.013 cm(2), and a linear dynamic range of approximate to 75 dB. Importantly, the CISe QDs layer makes the perovskite denser and more hydrophobic, thus improves the environmental and thermal stability of the detector, even extends the working temperature to exceeding 150 degrees C. The design concept and the considerable performance of this novel device provide a reference value for polychromatic light detection.
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