Modulation spectroscopy study on additive-induced efficiency enhancement of PTB7:PC71BM organic photovoltaic devices

2021 
Abstract Additives have been known to play an important role for improving the photovoltaic performance of organic solar cells. However, the reasons why additives improve the performance have not been clearly known yet. We employed an electrical modulated optical spectroscopy to investigate the relationship between the photovoltaic performance and additive concentration in organic photovoltaic devices. Our measured modulation spectra of a sample without additive showed both first- (-α’) and second-derivative (α”) components of the absorption spectrum. The second-derivative (α”) component in the modulation spectrum increased with the additive concentration. These results indicate that the sample without additive contains both localized (or Frenkel type) and relatively delocalized excitons and the added additive results in a significant increase of the relatively delocalized excitons. We conclude that the increased delocalized excitons lead to a significant additive-induced improvement of the photovoltaic-device performance.
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