Abstract
We use frequency-modulated electrostatic force microscopy to track changes in cantilever quality factor (Q) as a function of photochemical damage in a model organic photovoltaic system poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4, 5-b′]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3, 4-b]thiophenediyl]] (PTB7) and 3′H-cyclopropa[8,25][5,6]fullerene-C71- D5h(6)-3′-butanoic acid, 3′-phenyl-, methyl ester (PC 71BM). We correlate local Q factor imaging with macroscopic device performance and show that, for this system, changes in cantilever Q correlate well with changes in external quantum efficiency and can thus be used to monitor local photochemical damage over the entire functional lifetime of a PTB7:PC71BM solar cell. We explore how Q imaging is affected by the choice of cantilever resonance frequency. Finally, we use Q imaging to elucidate the differences in the evolution of nanoscale structure in the photochemical damage occurring in PTB7:PC71BM solar cells processed with and without the solvent additive 1,8-diiodooctane (DIO). We show that processing with DIO not only yields a preferable morphology for uniform performance across the surface of the device but also enhances the stability of PTB7:PC 71BM solar cells-an effect that can be predicted based on the local Q images.
Original language | English |
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Pages (from-to) | 10405-10413 |
Number of pages | 9 |
Journal | ACS Nano |
Volume | 7 |
Issue number | 11 |
DOIs | |
State | Published - Nov 26 2013 |
Funding
Keywords
- PTB7
- atomic force microscopy
- dissipation imaging
- organic solar cells
- photo-oxidation
- photodegradation
- photovoltaics