| 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. |
- Tang, Zheng, et al.
(författare)
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Universal modification of poor cathodes into good ones by a polymer interlayer for high performance reversed organic solar cells
- 2014
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- In organic bulk-heterojunction solar cells, energy losses at the active layer/electrode interface are often observed. Modification of these interfaces with organic interlayers optimizes charge carrier injection and extraction and thus improves device performance. In this work, the effects of cathode modification by a conjugated polymer interlayer PFPA1 on the performance of reversed organic solar cells (substrate/cathode/active layer/transparent anode) based on different active material systems and different substrate electrodes are systematically investigated. A reduction of the work function irrespective of the substrate cathode used is observed upon the deposition of the PFPA1 interlayer; further related to an improved built-in electric field and open-circuit voltage. The amphiphilic character of the PFPA1 interlayer alters the surface energy of the substrate cathode, leading to the formation of a better active layer morphology aiding efficient exciton dissociation and photocurrent extraction in the modified solar cells. Hence, internal quantum efficiency is found significantly higher than that of their unmodified counterparts, while optically, the modified and unmodified solar cells are identical. Moreover, the deep HOMO of the PFPA1 interlayer improves the selectivity for all investigated substrate cathodes, thus enhancing the fill factor. We demonstrate a possibility of improving photovoltaic performance of reversed solar cells via a simple and universal interface modification and provide the basic guidelines for development and characterization of interface materials for organic solar cells in general.
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