| 1. |
- Bakulin, Artem A., et al.
(författare)
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Morphology, Temperature, and Field Dependence Separation in High-Efficiency Solar Cells Based on Polyquinoxaline Copolymer
- 2016
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Ingår i: The Journal of Physical Chemistry C. - : AMER CHEMICAL SOC. - 1932-7447 .- 1932-7455. ; 120:8, s. 4219-4226
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Tidskriftsartikel (refereegranskat)abstract
- Charge separation and recombination are key processes determining the performance of organic optoelectronic devices. Here we combine photoluminescence and photovoltaic characterization of organic solar cell devices with ultrafast multipulse photocurrent spectroscopy to investigate charge generation mechanisms in the organic photovoltaic devices based on a blend of an alternating polyquinoxaline copolymer with fullerene. The combined use of these techniques enables the determination of the contributions of geminate and bimolecular processes to the solar cell performance. We observe that charge separation is not a temperature-activated process in the studied materials. At the same time, the generation of free charges shows a dear external field and morphology dependence. This indicates that the critical step of charge separation involves the nonequilibrium state that is formed at early times after photoexcitation, when the polaronic localization is not yet complete. This work reveals new aspects of molecular level charge dynamics in the organic light-conversion systems.
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| 2. |
- Chen, Xian-Kai, et al.
(författare)
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A unified description of non-radiative voltage losses in organic solar cells
- 2021
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Ingår i: Nature Energy. - : Springer Nature. - 2058-7546. ; 6:8, s. 799-806
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Tidskriftsartikel (refereegranskat)abstract
- Organic solar cells based on non-fullerene acceptors have enabled high efficiencies yet their charge dynamics and its impact on the photovoltaic parameters are not fully understood. Now, Chen et al. provide a general description of non-radiative voltage losses in both fullerene and non-fullerene solar cells. Recent advances in organic solar cells based on non-fullerene acceptors (NFAs) come with reduced non-radiative voltage losses (Delta V-nr). Here we show that, in contrast to the energy-gap-law dependence observed in conventional donor:fullerene blends, the Delta V-nr values in state-of-the-art donor:NFA organic solar cells show no correlation with the energies of charge-transfer electronic states at donor:acceptor interfaces. By combining temperature-dependent electroluminescence experiments and dynamic vibronic simulations, we provide a unified description of Delta V-nr for both fullerene- and NFA-based devices. We highlight the critical role that the thermal population of local exciton states plays in low-Delta V-nr systems. An important finding is that the photoluminescence yield of the pristine materials defines the lower limit of Delta V-nr. We also demonstrate that the reduction in Delta V-nr (for example, <0.2 V) can be obtained without sacrificing charge generation efficiency. Our work suggests designing donor and acceptor materials with high luminescence efficiency and complementary optical absorption bands extending into the near-infrared region.
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| 3. |
- Cui, Yong, et al.
(författare)
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Wide-gap non-fullerene acceptor enabling high-performance organic photovoltaic cells for indoor applications
- 2019
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Ingår i: NATURE ENERGY. - : NATURE PUBLISHING GROUP. - 2058-7546. ; 4:9, s. 768-775
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Tidskriftsartikel (refereegranskat)abstract
- Organic photovoltaic cells are potential candidates to drive low power consumption off-grid electronics for indoor applications. However, their power conversion efficiency is still limited by relatively large losses in the open-circuit voltage and a non-optimal absorption spectrum for indoor illumination. Here, we carefully designed a non-fullerene acceptor named IO-4CI and blend it with a polymer donor named PBDB-TF to obtain a photoactive layer whose absorption spectrum matches that of indoor light sources. The photovoltaic characterizations reveal a low energy loss below 0.60 eV. As a result, the organic photovoltaic cell (1 cm(2)) shows a power conversion efficiency of 26.1% with an open-circuit voltage of 1.10 V under a light-emitting diode illumination of 1,000 lux (2,700 K). We also fabricated a large-area cell (4 cm(2)) through the blade-coating method. Our cell shows an excellent stability, maintaining its initial photovoltaic performance under continuous illumination of the indoor light source for 1,000 hours.
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| 4. |
- Diaz de Zerio Mendaza, Amaia, 1986, et al.
(författare)
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Neat C60:C70 buckminsterfullerene mixtures enhance polymer solar cell performance
- 2014
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 2:35, s. 14354-14359
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate that bulk-heterojunction blends based on neat, unsubstituted buckminsterfullerenes (C60, C70) and a thiophene–quinoxaline copolymer (TQ1) can be readily processed from solution. Atomic force and transmission electron microscopy as well as photoluminescence spectroscopy reveal that thin films with a fine-grained nanostructure can be spin-coated, which display a good photovoltaic performance. Replacement of substituted fullerenes with C60 or C70 only results in a small drop in open-circuit voltage from 0.9 V to about 0.8 V. Thus, a power conversion efficiency of up to 2.9% can be maintained if C70 is used as the acceptor material. Further improvement in photovoltaic performance to 3.6% is achieved, accompanied by a high internal quantum efficiency of 75%, if a 1 : 1 C60:C70 mixture is used as the acceptor material, due to its improved solubility in ortho-dichlorobenzene.
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| 5. |
- Gao, Feng, et al.
(författare)
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Charge generation in polymer-fullerene bulk-heterojunction solar cells
- 2014
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 16:38, s. 20291-20304
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Tidskriftsartikel (refereegranskat)abstract
- Charge generation in organic solar cells is a fundamental yet heavily debated issue. This article gives a balanced review of different mechanisms proposed to explain efficient charge generation in polymer-fullerene bulk-heterojunction solar cells. We discuss the effect of charge-transfer states, excess energy, external electric field, temperature, disorder of the materials, and delocalisation of the charge carriers on charge generation. Although a general consensus has not been reached yet, recent findings, based on both steady-state and transient measurements, have significantly advanced our understanding of this process.
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| 6. |
- Gao, Feng, et al.
(författare)
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Temperature Dependence of Charge Carrier Generation in Organic Photovoltaics
- 2015
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Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 114:12, s. 128701-
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Tidskriftsartikel (refereegranskat)abstract
- The charge generation mechanism in organic photovoltaics is a fundamental yet heavily debated issue. All the generated charges recombine at the open-circuit voltage (VOC), so that investigation of recombined charges at VOC provides a unique approach to understanding charge generation. At low temperatures, we observe a decrease of VOC, which is attributed to reduced charge separation. Comparison between benchmark polymer: fullerene and polymer: polymer blends highlights the critical role of charge delocalization in charge separation and emphasizes the importance of entropy in charge generation.
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| 7. |
- Gao, Feng, et al.
(författare)
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The Effect of Processing Additives on Energetic Disorder in Highly Efficient Organic Photovoltaics : A Case Study on PBDTTT-C-T:PC71BM
- 2015
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Ingår i: Advanced Materials. - : Wiley-VCH Verlag. - 0935-9648 .- 1521-4095. ; 27:26, s. 3868-3873
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Tidskriftsartikel (refereegranskat)abstract
- Energetic disorder, an important parameter affecting the performance of organic photovoltaics, is significantly decreased upon the addition of processing additives in a highly efficient benzodithiophene-based copolymer blend (PBDTTT-C-T:PC71BM). Wide-angle and small-angle X-ray scattering measurements suggest that the origin of this reduced energetic disorder is due to increased aggregation and a larger average fullerene domain size together with purer phases.
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| 8. |
- Hou, Jianhui, et al.
(författare)
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Organic solar cells based on non-fullerene acceptors
- 2018
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Ingår i: Nature Materials. - : Nature Publishing Group. - 1476-1122 .- 1476-4660. ; 17:2, s. 119-128
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Forskningsöversikt (refereegranskat)abstract
- Organic solar cells (OSCs) have been dominated by donor: acceptor blends based on fullerene acceptors for over two decades. This situation has changed recently, with non-fullerene (NF) OSCs developing very quickly. The power conversion efficiencies of NF OSCs have now reached a value of over 13%, which is higher than the best fullerene-based OSCs. NF acceptors show great tunability in absorption spectra and electron energy levels, providing a wide range of new opportunities. The coexistence of low voltage losses and high current generation indicates that new regimes of device physics and photophysics are reached in these systems. This Review highlights these opportunities made possible by NF acceptors, and also discuss the challenges facing the development of NF OSCs for practical applications.
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| 9. |
- Kroon, Renee, 1982, et al.
(författare)
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A New Tetracyclic Lactam Building Block for Thick, Broad-Bandgap Photovoltaics
- 2014
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society. - 0002-7863 .- 1520-5126. ; 136:33, s. 11578-11581
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Tidskriftsartikel (refereegranskat)abstract
- A new tetracyclic lactam building block for polymer semiconductors is reported that was designed to combine the many favorable properties that larger fused and/or amide-containing building blocks can induce, including improved solid-state packing, high charge carrier mobility, and improved charge separation. Copolymerization with thiophene resulted in a semicrystalline conjugated polymer, PTNT, with a broad bandgap of 2.2 eV. Grazing incidence wide-angle X-ray scattering of PTNT thin films revealed a strong tendency for face-on pi-stacking of the polymer backbone, which was retained in PTNT:firllerene blends. Corresponding solar cells featured a high open-circuit voltage of 0.9 V, a fill factor around 0.6, and a power conversion efficiency as high as 596 for greater than200 nm thick active layers, regardless of variations in blend stoichiometry and nanostructure. Moreover, efficiencies of greater than4% could be retained when thick active layers of similar to 400 rim were employed. Overall, these values are the highest reported for a conjugated polymer with such a broad bandgap and are unprecedented in materials for tandem and particularly ternary blend photovoltaics. Hence, the newly developed tetracyclic lactam unit has significant potential as a conjugated building block in future organic electronic materials.
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| 10. |
- Li, Yongxi, et al.
(författare)
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Non-fullerene acceptor with low energy loss and high external quantum efficiency: towards high performance polymer solar cells
- 2016
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry. - 2050-7488 .- 2050-7496. ; 4:16, s. 5890-5897
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Tidskriftsartikel (refereegranskat)abstract
- A non-fullerene electron acceptor bearing a fused 10-heterocyclic ring (indacenodithiophenoindacenodithiophene) with a narrow band gap (similar to 1.5 eV) was designed and synthesized. It possesses excellent planarity and enhanced effective conjugation length compared to previously reported fused-ring electron acceptors. When this acceptor was paired with PTB7-Th and applied in polymer solar cells, a power conversion efficiency of 6.5% was achieved with a high open circuit voltage of 0.94 V. More significantly, an energy loss as low as 0.59 eV and an external quantum efficiency as high as 63% were obtained simultaneously.
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