2021/10/28 by Alberto Privitera, Privitera, Alberto, Jeannine Grüne +17
Chemistry · Engineering · #Applied Physics (physics.app-ph) #FOS: Physical sciences #Materials Science (cond-mat.mtrl-sci) #Molecular Junctions and Nanostructures #Organic Electronics and Photovoltaics #Photochemistry and Electron Transfer Studies
paper · pdf · doi:10.48550/arxiv.2110.15393
openalex publication_date 2021/10/28 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
Organic solar cells (OSCs) have recently shown a rapid improvement in their\nperformance, bringing power conversion efficiencies (PCEs) closer to the point\nwhere commercial applications of the technology become viable. However, the low\nopen-circuit voltage (Voc) of OSCs relative to their optical gap still limits\nPCEs to below 20%. A key factor contributing to the large Voc deficit in OSCs\nis non-radiative recombination to spin-triplet excitons, which is widely, but\nnot universally, observed in blends using both fullerene and non-fullerene\nelectron acceptors. Here, we present an experimental framework that combines\ntime resolved optical and magnetic resonance spectroscopies to detect triplet\nexcitons and identify their formation mechanisms. We apply our methodology to\ntwo well-studied polymer:fullerene systems, PM6:PC60BM and PTB7-Th:PC60BM,\nenabling us to selectively investigate distinct triplet formation pathways. In\ncontrast to the more efficient non-fullerene acceptor systems that show only\ntriplet states formed via non-geminate recombination, the fullerene systems\nalso show significant triplet formation via geminate processes. We associate\nthis with electrons trapped at the isolated fullerenes that sit within the\nalkyl sidechains of the donor polymers. Thus, our model study demonstrates how\nthese complex and overlapping processes can be successfully deconvoluted to\nreveal the intricacies of triplet generation dynamics in OSC blends.\n