AI Article Synopsis
- The nanoscale structure and high charge densities in organic photovoltaics (OPVs) result in frequent interactions between electrons and holes, which can create low-energy triplet excitons that negatively impact performance.
- Using time-resolved optical spectroscopy, researchers studied how solvent additives like 1,8-octanedithiol (ODT) influence triplet dynamics and charge recombination in a specific OPV blend.
- The addition of ODT improved the internal quantum efficiency from 48% to 65%, but also increased the rate of bimolecular triplet formation, which now contributed to all charge recombination.
Article Abstract
The nanoscale morphology and high charge densities in organic photovoltaics (OPVs) lead to a high rate of bimolecular encounters between spin-uncorrelated electrons and holes. This process can lead to the formation of low-energy triplet excitons on the donor polymer that decay nonradiatively and limit the device performance. We use time-resolved optical spectroscopy to characterize the effect of morphology through the use of solvent additives such as 1,8-octanedithiol (ODT) on triplet dynamics and charge recombination in blends of poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b']-dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] and [6,6]-phenyl-C71-butyric acid methyl ester. This is an attractive OPV system since the extended absorption of the polymer into the near-infrared gives good coverage of the solar spectrum, but nevertheless, the internal quantum efficiency (IQE) has not been reported to be higher than ~65% under short circuit conditions. We find that, without ODT, the IQE is 48% and 16% of excitations decay via bimolecular triplet formation. With ODT treatment, which improves crystallinity and carrier mobility, the IQE increases to 65%, but bimolecular triplet formation significantly increases and now accounts for all of the recombination (35% of charges).
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