Short Excited State Lifetimes Mediate Charge Recombination Losses in Organic Solar Cell Blends with Low Charge Transfer Driving Force

Shivhare, Rishi; Moore, Gareth John; Hofacker, Andreas; Hutsch, Sebastian; Zhong, Yufei; Hambsch, Mike; Erdmann, Tim; Mannsfeld, Stefan C.B.; Ortmann, Frank; Banerji, Natalie (2021). Short Excited State Lifetimes Mediate Charge Recombination Losses in Organic Solar Cell Blends with Low Charge Transfer Driving Force. Advanced materials, 34(22), p. 2101784. Wiley-VCH 10.1002/adma.202101784

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A blend of a low-optical-gap diketopyrrolopyrrole polymer and a fullerene derivative, with near-zero driving force for electron transfer, is investigated. Using femtosecond transient absorption and electroabsorption spectroscopy, the charge transfer (CT) and recombination dynamics as well as the early-time transport are quantified. Electron transfer is ultrafast, consistent with a Marcus–Levich–Jortner description. However, significant charge recombination and unusually short excited (S1) and CT state lifetimes (≈14 ps) are observed. At low S1–CT offset, a short S1 lifetime mediates charge recombination because: i) back-transfer from the CT to the S1 state followed by S1 recombination occurs and ii) additional S1–CT hybridization decreases the CT lifetime. Both effects are confirmed by density functional theory calculations. In addition, relatively slow (tens of picoseconds) dissociation of charges from the CT state is observed, due to low local charge mobility. Simulations using a four-state kinetic model entailing the effects of energetic disorder reveal that the free charge yield can be increased from the observed 12% to 60% by increasing the S1 and CT lifetimes to 150 ps. Alternatively, decreasing the interfacial CT state disorder while increasing bulk disorder of free charges enhances the yield to 65% in spite of the short lifetimes.

Item Type:

Journal Article (Original Article)

Division/Institute:

08 Faculty of Science > Department of Chemistry, Biochemistry and Pharmaceutical Sciences (DCBP)

UniBE Contributor:

Shivhare, Rishi Ramdas; Moore, Gareth John; Zhong, Yufei and Banerji, Natalie

Subjects:

500 Science > 540 Chemistry

ISSN:

0935-9648

Publisher:

Wiley-VCH

Funders:

[4] Swiss National Science Foundation

Language:

English

Submitter:

Olivier Nicolas Ludovic Bardagot

Date Deposited:

07 Oct 2021 11:22

Last Modified:

05 Jun 2022 01:45

Publisher DOI:

10.1002/adma.202101784

Related URLs:

Additional Information:

Funders:
Swiss National Science Foundation
Type: Project Funding, Grant number: 200020_184819

University of Bern

BORIS DOI:

10.48350/159526

URI:

https://boris.unibe.ch/id/eprint/159526

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