Importance of Energetic Driving Force for Efficient Charge Separation in Non-fullerene Organic Solar Cells
SAFAKATH KARUTHEDATH a, Julien Gorenflot a, Anastasia Markina b, Yuliar Firdaus a, Ahmed H. Balawi a, Thomas D. Anthopoulos a, Denis Andrienko b, Frédéric Laquai a
a King Abdullah University of Science and Technology (KAUST) - Saudi Arabia, 4700 King Abdullah University of Science and Technology (KAUST), Thuwal, Saudi Arabia
b Max Planck Institute for Polymer Research, Mainz, Ackermannweg, 10, Mainz, Germany
Asia-Pacific International Conference on Perovskite, Organic Photovoltaics and Optoelectronics
Proceedings of Asia-Pacific International Conference on Perovskite, Organic Photovoltaics and Optoelectronics (IPEROP20)
Tsukuba-shi, Japan, 2020 January 20th - 22nd
Organizers: Michio Kondo and Takurou Murakami
Oral, SAFAKATH KARUTHEDATH, presentation 018
Publication date: 14th October 2019

The minimum energy offset required to ensure efficient charge separation at organic donor-acceptor heterojunctions is a matter of current debate.1-2 Here, we investigate the charge generation in a series of donor – acceptor bulk heterojunction blends including the small molecule donor DR3, two high-efficiency donor polymers (PBDB-T-2F, PCE10), and eight different non-fullerene acceptors (NFA), spanning a power conversion efficiency range from <1% to above 15%.

In principle, both electron affinity (EA) and ionization energy (IE) offsets should equally control the charge generation. However, we demonstrate that despite large EA offsets, it is the IE offset, which controls both the exciton quenching and charge separation efficiency, as ultrafast energy transfer from the donor to the acceptor competes with photoinduced electron transfer. This implies, the IE offset cannot be reduced to zero to maximize the Voc as it leads to inefficient exciton quenching and reduced charge separation efficiencies and in turn to lower device photocurrents and performance.

This research work is based upon work supported by the King Abdullah University of Science and Technology (KAUST) Office of Sponsored Research (OSR) under Award No: OSR-2018-CARF/CCF-3079 and Award No. OSR-CRG2018-3746. D.A. acknowledges funding from the BMBF grant InterPhase and MESOMERIE (FKZ 13N13661, FKZ 13N13656) and the European Union Horizon 2020 research and innovation program ‘‘Widening materials models’’ under Grant Agreement No. 646259 (MOSTOPHOS). D.A. also acknowledges the KAUST PSE Division for hosting his sabbatical in the framework of the Division’s Visiting Faculty program. A.M. acknowledges postdoctoral support of the Alexander von Humboldt Foundation.

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