| 1. |
- Bergqvist, Jonas, et al.
(författare)
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Sub-glass transition annealing enhances polymer solar cell performance
- 2014
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry. - 2050-7488. ; 2:17, s. 6146-6152
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Tidskriftsartikel (refereegranskat)abstract
- Thermal annealing of non-crystalline polymer: fullerene blends typically results in a drastic decrease in solar cell performance. In particular aggressive annealing above the glass transition temperature results in a detrimental coarsening of the blend nanostructure. We demonstrate that mild annealing below the glass transition temperature is a viable avenue to control the nanostructure of a non-crystalline thiophene-quinoxaline copolymer: fullerene blend. Direct imaging methods indicate that coarsening of the blend nanostructure can be avoided. However, a combination of absorption and luminescence spectroscopy reveals that local changes in the polymer conformation as well as limited fullerene aggregation are permitted to occur. As a result, we are able to optimise the solar cell performance evenly across different positions of the coated area, which is a necessary criterion for large-scale, high throughput production.
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| 2. |
- Bergqvist, J., et al.
(författare)
-
Sub-glass transition annealing enhances polymer solar cell performance
- 2014
-
Ingår i: Journal of Materials Chemistry A. - 2050-7488 .- 2050-7496. ; 2:17, s. 6146-6152
-
Tidskriftsartikel (refereegranskat)abstract
- Thermal annealing of non-crystalline polymer:fullerene blends typically results in a drastic decrease in solar cell performance. In particular aggressive annealing above the glass transition temperature results in a detrimental coarsening of the blend nanostructure. We demonstrate that mild annealing below the glass transition temperature is a viable avenue to control the nanostructure of a non-crystalline thiophene–quinoxaline copolymer:fullerene blend. Direct imaging methods indicate that coarsening of the blend nanostructure can be avoided. However, a combination of absorption and luminescence spectroscopy reveals that local changes in the polymer conformation as well as limited fullerene aggregation are permitted to occur. As a result, we are able to optimise the solar cell performance evenly across different positions of the coated area, which is a necessary criterion for large-scale, high throughput production.
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| 3. |
- Campoy-Quiles, M., et al.
(författare)
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On the complex refractive index of polymer:fullerene photovoltaic blends
- 2014
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 571:P3, s. 371-376
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Tidskriftsartikel (refereegranskat)abstract
- We present a detailed investigation of the refractive index of polymer:fullerene blends for photovoltaic applications. The donor polymers poly[2,7-(9,9-dioctylfluorene)-alt-5,5-(4,7-di-2-thienyl-2,1,3-benzothiadiazole)] (APFO3), poly[2,3-bis-(3-octyloxyphenyl)quinoxaline-5,8-diyl-alt-thiophene-2,5-diyl] (TQ1), and poly[2,7-(9,9-dioctylfluorene)-alt-5,5-(5,10-di-2-thienyl-2,3,7,8-tetraphenyl-pyrazino[2,3-g]quinoxaline)] (APFO-Green9) were blended with either [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) or [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM). We measured variable angle spectroscopic ellipsometry for three systems, namely APFO3:PCBM, TQ1:PC71BM and APFO-Green9:PC71BM, as a function of composition and analyze the data employing a number of models. We found that Bruggeman effective medium approximations (EMA) are not precise for the description of the optical properties of these blends. This is due to a number of reasons. First, we find that there are energy shifts associated to changes in conjugation length that cannot be accounted for using EMA. Second, blending results in a strong reduction of anisotropy. Finally, our data suggest that there is some degree of vertical segregation between components. Therefore, our results support the idea that the optical properties of polymer:fullerene mixtures should be treated as alloys rather than non-interacting blends.
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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. |
- Henriksson, Patrik, 1983, et al.
(författare)
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Stability study of quinoxaline and pyrido pyrazine based co-polymers for solar cell applications
- 2014
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Ingår i: Solar Energy Materials and Solar Cells. - : Elsevier BV. - 0927-0248 .- 1879-3398. ; 130, s. 138-143
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Tidskriftsartikel (refereegranskat)abstract
- We present two co-polymer families; one based on a thiophene-quinoxaline unit and one on a thiophene-pyrido pyrazine unit. Co-polymerization of these monomers with thiophene-hexylthiophene was performed to create polymers with an optical absorption that fully covers the visible part of the solar spectrum with the aim to enhance the solar cell performances of these polymers. We have also studied how increasing the fraction of thiophene-hexylthiophene affects the photo-oxidative stability of these polymers. Thiophene-pyrido pyrazine solar cells displayed increased device efficiency upon addition of the thiophene-hexylthiophene and, in addition, the stability is retained upon inclusion of these units. In contrast, we found that for the thiophene-quinoxaline based co-polymer, both device efficiency and stability decreased with increasing thiophene-hexylthiophene fraction. Moreover, our results indicate that the photo-oxidative stability of the thiophene-quinoxaline co-polymer is independent of the polymer molecular weight as well as of the film thickness.
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| 6. |
- 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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| 7. |
- Lindqvist, Camilla, et al.
(författare)
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Fullerene mixtures enhance the thermal stability of a non-crystalline polymer solar cell blend
- 2014
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Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 104:15, s. 153301-
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Tidskriftsartikel (refereegranskat)abstract
- Printing of polymer: fullerene solar cells at high speed requires annealing at temperatures up to 140 degrees C. However, bulk-heterojunction blends that comprise a non-crystalline donor polymer often suffer from insufficient thermal stability and hence rapidly coarsen upon annealing above the glass transition temperature of the blend. In addition, micrometer-sized fullerene crystals grow, which are detrimental for the solar cell performance. In this manuscript, we present a strategy to limit fullerene crystallization, which is based on the use of fullerene mixtures of the two most common derivatives, PC61BM and PC71BM, as the acceptor material. Blends of this fullerene mixture and a non-crystalline thiophene-quinoxaline copolymer display considerably enhanced thermal stability and largely retain their photovoltaic performance upon annealing at elevated temperatures as high as 170 degrees C.
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| 8. |
- Lindqvist, Camilla, 1985, et al.
(författare)
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Fullerene Nucleating Agents: A Route Towards Thermally Stable Photovoltaic Blends
- 2014
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Ingår i: Advanced Energy Materials. - : Wiley. - 1614-6840 .- 1614-6832. ; 4:9, s. 1301437-
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Tidskriftsartikel (refereegranskat)abstract
- The bulk-heterojunction nanostructure of non-crystalline polymer: fullerene blends has the tendency to rapidly coarsen when heated above its glass transition temperature, which represents an important degradation mechanism. We demonstrate that fullerene nucleating agents can be used to thermally arrest the nanostructure of photovoltaic blends that comprise a non-crystalline thiophene-quinoxaline copolymer and the widely used fullerene derivative [6,6]-phenyl-C-61-butyric acid methyl ester (PCBM). To this end, C-60 fullerene is employed to efficiently nucleate PCBM crystallization. Sub-micrometer-sized fullerene crystals are formed when as little as 2 wt% C-60 with respect to PCBM is added to the blend. These reach an average size of only 200 nanometers upon introduction of more than 8 wt% C-60. Solar cells based on C-60-nucleated blends indicate significantly improved thermal stability of the bulk-heterojunction nanostructure even after annealing at an elevated temperature of 130 degrees C, which lies above the glass transition temperature of the blend. Moreover, we find that various other compounds, including C-70 fullerene, single-walled carbon nanotubes, and sodium benzoate, as well as a number of commercial nucleating agents-commonly used to clarify isotactic polypropylene-permit to control crystallization of the fullerene phase.
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| 9. |
- Ma, Zaifei, et al.
(författare)
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Structure-Property Relationships of Oligothiophene-Isoindigo Polymers for Efficient Bulk-Heterojunction Solar Cells
- 2014
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Ingår i: energy and environmental science. - : Royal Society of Chemistry. - 1754-5692. ; 17:1, s. 361-369
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Tidskriftsartikel (refereegranskat)abstract
- A series of alternating oligothiophene (nT)-isoindigo (I) copolymers (PnTI) were synthesized to investigate the influence of the oligothiophene block length on the photovoltaic (PV) properties of PnTI:PCBM bulk-heterojunction blends. Our study indicates that the number of thiophene rings (n) in the repeating unit alters both, polymer crystallinity and polymer-fullerene interfacial energetics, which results in a decreasing open-circuit voltage (Voc) of the solar cells with increasing n. The short-circuit current density (Jsc) of P1TI:PCBM devices is limited by the absence of a significant driving force for electron transfer. Instead, blends based on P5TI and P6TI feature large polymer domains, which limit charge generation and thus Jsc. The best PV performance with a power conversion efficiency of up to 6.9% was achieved with devices based on P3TI, where a combination of favorable morphology and optimal interface energy level offset ensures efficient exciton separation and charge generation. The structure-property relationship demonstrated in this work is a valuable guideline for the design of high performance polymers with small energy losses during the charge generation process, allowing for the fabrication of efficient solar cells that combine a minimal loss in Voc with a high Jsc.
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