Abstract
The charge generation and recombination processes following photoexcitation of a low-bandgap polymer:perylene diimide photovoltaic blend are investigated by transient absorption pump-probe spectroscopy covering a dynamic range from femto- to microseconds to get insight into the efficiency-limiting photophysical processes. The photoinduced electron transfer from the polymer to the perylene acceptor takes up to several tens of picoseconds, and its efficiency is only half of that in a polymer:fullerene blend. This reduces the short-circuit current. Time-delayed collection field experiments reveal that the subsequent charge separation is strongly field-dependent, limiting the fill factor and lowering the short-circuit current in polymer:PDI devices. Upon excitation of the acceptor in the low-bandgap polymer blend, the PDI exciton undergoes charge transfer on a time scale of several tens of picoseconds. However, a significant fraction of the charges generated at the interface are quickly lost because of fast geminate recombination. This reduces the short-circuit current even further, leading to a scenario in which only around 25% of the initial photoexcitations generate free charges that can potentially contribute to the photocurrent. In summary, the key photophysical limitations of perylene diimide as an acceptor in low-bandgap polymer blends appear at the interface between the materials, with the kinetics of both charge generation and separation inhibited as compared to that of fullerenes.
Original language | English (US) |
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Pages (from-to) | 20077-20085 |
Number of pages | 9 |
Journal | JOURNAL OF PHYSICAL CHEMISTRY C |
Volume | 118 |
Issue number | 35 |
DOIs | |
State | Published - Sep 4 2014 |
Externally published | Yes |
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- General Energy
- Surfaces, Coatings and Films
- Physical and Theoretical Chemistry