Geminate and Nongeminate Pathways for Triplet Exciton Formation in Organic Solar Cells
Abstract
Organic solar cells (OSCs) have recently shown a rapid improvement in their performance, bringing power conversion efficiencies to above 18%. However, the open‐circuit voltage of OSCs remains low relative to their optical gap and this currently limits efficiency. Recombination to spin‐triplet excitons is a key contributing factor, and is widely, but not universally, observed in donor–acceptor blends using both fullerene and nonfullerenes as electron acceptors. Here, an experimental framework that combines time‐resolved optical and magnetic resonance spectroscopies to detect triplet excitons and identify their formation mechanisms, is reported. The methodology is applied to two well‐studied polymer:fullerene systems, PM6:PC60BM and PTB7‐Th:PC60BM. In contrast to the more efficient nonfullerene acceptor systems that show only triplet states formed via nongeminate recombination, the fullerene systems also show significant triplet formation via geminate processes. This requires that geminate electron–hole pairs be trapped long enough to allow intersystem crossing. It is proposed that this is a general feature of fullerene acceptor systems, where isolated fullerenes are known to intercalate within the alkyl sidechains of the donor polymers. Thus, the study demonstrates that engineering good donor and acceptor domain purity is key for suppressing losses via triplet excitons in OSCs.
Document Details
- Document Type
- Pub Defense Publication
- Publication Date
- Mar 16, 2022
- Source ID
- 10.1002/aenm.202103944
Entities
People
- Akchheta Karki
- Alberto Privitera
- Alexander J Gillett
- Andreas Sperlich
- Jeannine Grüne
- Moritz K. Riede
- Richard Friend
- Thuc‐quyen Nguyen
- Vladimir Dyakonov
- William K. Myers
Organizations
- Engineering and Physical Sciences Research Council
- European Research Council
- German Research Foundation
- Office of Naval Research
- Simons Foundation
- University of California, Santa Barbara
- University of Cambridge
- University of Oxford
- University of Turin
- University of Würzburg