Charge Separation from Triplet Excited States in Nonfullerene Acceptor‐Based Organic Solar Cells

Author:

Kohzuki Kazuki1,Shirouchi Rei1,Natsuda Shin-ichiro1,Saito Toshiharu1,Sakamoto Yuji1,Tamai Yasunari1ORCID

Affiliation:

1. Department of Polymer Chemistry Graduate School of Engineering Kyoto University Katsura, Nishikyo Kyoto 615-8510 Japan

Abstract

Suppressing charge recombination is pivotal for further improving the power conversion efficiency of organic solar cells (OSCs). The bimolecular recombination of free charge carriers leads to the formation of both singlet and triplet charge transfer (CT) states at a ratio of 1:3 when considering simple spin statistics, meaning that charge recombination via the triplet excited state is the main deactivation channel for OSCs. Although the formation of local triplet excitons through back charge transfer from triplet CT states is thought to be a terminal loss process, it is shown that charge separation from triplet excitons can occur in nonfullerene acceptor (NFA)‐based OSCs. To reveal the triplet exciton dynamics, a triplet sensitizer PtTPBP is doped into an OSC consisting of PM6 and Y6 as an electron donor and acceptor, respectively. Upon photoexcitation of PtTPBP, triplet excitons are formed, which subsequently transfer their energy to Y6, resulting in Y6 triplet excitons formation. Based on transient absorption and external quantum efficiency measurements, clear experimental evidence of charge photogeneration from Y6 triplet excitons at the PM6:Y6 interface is provided. This study highlights the importance of minimizing the energy difference between the singlet and triplet excited states of NFAs to suppress charge recombination.

Funder

Japan Society for the Promotion of Science

Publisher

Wiley

Subject

Electrical and Electronic Engineering,Energy Engineering and Power Technology,Atomic and Molecular Physics, and Optics,Electronic, Optical and Magnetic Materials

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