Energy Focus: Low bandgap, silole-containing heteroarene polymers developed for solar cells
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e-containing heteroarene polymers developed for solar cells
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Nano Focus Low-temperature aqueous synthesis yields large surface area tin oxide nanocrystals
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in oxide is a critical component of optical devices, lithium batteries, and conducting coatings, and used as a catalyst besides many other applications. Development of tin oxide particles with high surface area is particularly critical for use in chemical sensors and dyesensitive solar cells. Researchers from the National Institute of Advanced Industrial Science and Technology (AIST) in Japan have prepared tin oxide nanocrystals with unprecedented surface
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MRS BULLETIN
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VOLUME 35 • NOVEMBER 2010
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area using novel nanofabrication techniques. As reported in the August issue of the Journal of the American Ceramic Society (DOI: 10.1111/j.15512916.201 0.03680.x; p. 2140), Y. Masuda and co-workers prepared nanocrystals by crystallization in the aqueous phase with minimal application of heat. Previous methods for fabricating particles have t ypi c a l l y involved hightemperature annealing that causes aggregation and deformation resulting in reduced specific
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much broader and at longer wavelengths than PBSTBT’s, which the researchers said is due to the presence of two thiophene units between the donor and the acceptor compared to PBSTBT. The researchers performed cyclic voltametry (CV) and density functional theory (DFT) calculations to determine HOMO and LUMO (lowest unoccupied molecular orbital) energy levels. Although DFT overestimated the orbital energy levels, it was consistent with the CV trends, for example, that the HOMO for PBSTBT lies lower in energy than PBSTDTBT’s HOMO. In addition, DFT predicts a lower lying HOMO for both polymers relative to their analogues where carbon replaces silicon, which is consistent with the researchers’ desire to increase the polymers’ open-circuit voltage. The researchers fabricated PSCs with each polymer and determined good photo conversion efficiency from 400 nm to 700 nm, with external quantum efficiencies about 50% and PCEs about 3.5%. The researchers said that their work “provides a new method for synthesizing silole-containing heteroarenes, which show great potential in organic electronics applications, such as FETs and PSCs.” Steven Trohalaki
Transmission electron micrographs of tin oxide nanosheets prepared by precipitation from low-temperature aqueous solution. Reproduced with permission from J. Am. Ceram. Soc. 93 (8) (2010) DOI: 10.1111/j.1551-2916.2010.03680.x; p. 2140. © 2010 The American Ceramic Society.
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