| 1. |
- Bakulin, Artem A., et al.
(author)
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Morphology, Temperature, and Field Dependence Separation in High-Efficiency Solar Cells Based on Polyquinoxaline Copolymer
- 2016
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In: The Journal of Physical Chemistry C. - : AMER CHEMICAL SOC. - 1932-7447 .- 1932-7455. ; 120:8, s. 4219-4226
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Journal article (peer-reviewed)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. |
- George, Zandra, 1985, et al.
(author)
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Two-in-one : Cathode modification and improved solar cell blend stability through addition of modified fullerenes
- 2016
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In: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 4:7, s. 2663-2669
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Journal article (peer-reviewed)abstract
- The synthesis of dual purpose modified fullerenes with pyridine-as well as amine-functional groups is reported. Addition of these fullerenes to a polymer : fullerene bulk-heterojunction blend based on a thiophene-quinoxaline donor polymer is found to modify the active layer/cathode interface of inverted solar cells (glass/ITO/active layer/MoO3/Al). In particular the open-circuit voltage of devices is increased from 0.1 V to about 0.7 V, which results in a drastic rise in photovoltaic performance with a power conversion efficiency of up to 3%. At the same time, presence of the functionalised fullerene additives prevents the detrimental formation of micrometre-sized fullerene crystals upon annealing at 140 degrees C. As a result, the device performance is retained, which promises significantly increased thermal stability of the bulk-heterojunction blend nanostructure.
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| 3. |
- Li, Yongxi, et al.
(author)
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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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In: Journal of Materials Chemistry A. - : Royal Society of Chemistry. - 2050-7488 .- 2050-7496. ; 4:16, s. 5890-5897
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Journal article (peer-reviewed)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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| 4. |
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| 5. |
- Wang, Chuanfei, et al.
(author)
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Low Band Gap Polymer Solar Cells With Minimal Voltage Losses
- 2016
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In: Advanced Energy Materials. - : Wiley. - 1614-6832 .- 1614-6840. ; 6:18
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Journal article (peer-reviewed)abstract
- One of the factors limiting the performance of organic solar cells (OSCs) is their large energy losses (E loss) in the conversion from photons to electrons, typically believed to be around 0.6 eV and often higher than those of inorganic solar cells. In this work, a novel low band gap polymer PIDTT-TID with a optical gap of 1.49 eV is synthesized and used as the donor combined with PC71BM in solar cells. These solar cells attain a good power conversion efficiency of 6.7% with a high open-circuit voltage of 1.0 V, leading to the E loss as low as 0.49 eV. A systematic study indicates that the driving force in this donor and acceptor system is sufficient for charge generation with the low E loss. This work pushes the minimal E loss of OSCs down to 0.49 eV, approaching the values of some inorganic and hybrid solar cells. It indicates the potential for further enhancement of the performance of OSCs by improving their V oc since the E loss can be minimized.
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| 6. |
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| 7. |
- Xia, Yuxin, et al.
(author)
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Inverted all-polymer solar cells based on a quinoxaline-thiophene/naphthalene-diimide polymer blend improved by annealing
- 2016
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In: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 4:10, s. 3835-3843
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Journal article (peer-reviewed)abstract
- We have investigated the effect of thermal annealing on the photovoltaic parameters of all-polymer solar cells based on a quinoxaline-thiophene donor polymer (TQ1) and a naphthalene diimide acceptor polymer (N2200). The annealed devices show a doubled power conversion efficiency compared to nonannealed devices, due to the higher short-circuit current (J(sc)) and fill factor (FF), but with a lower open circuit voltage (V-oc). On the basis of the morphology-mobility examination by several scanning force microscopy techniques, and by grazing-incidence wide-angle X-ray scattering, we conclude that better charge transport is achieved by higher order and better interconnected networks of the bulk heterojunction in the annealed active layers. The annealing improves charge transport and extends the conjugation length of the polymers, which do help in charge generation and meanwhile reduce recombination. Photoluminescence, electroluminescence, and light intensity dependence measurements reveal how this morphological change affects charge generation and recombination. As a result, the J(sc) and FF are significantly improved. However, the smaller band gap and the higher HOMO level of TQ1 upon annealing causes a lower V-oc. The blend of an amorphous polymer TQ1, and a semi-crystalline polymer N2200, can thus be modified by thermal annealing to double the power conversion efficiency.
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