TY - JOUR
T1 - Triplet Excitons and Associated Efficiency-Limiting Pathways in Organic Solar Cell Blends Based on (Non-) Halogenated PBDB-T and Y-Series
AU - Grüne, Jeannine
AU - Londi, Giacomo
AU - Gillett, Alexander J.
AU - Stähly, Basil
AU - Lulei, Sebastian
AU - Kotova, Maria
AU - Olivier, Yoann
AU - Dyakonov, Vladimir
AU - Sperlich, Andreas
N1 - Funding Information:
J.G., V.D., and A.S. acknowledge support by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) within the Research Training School “Molecular biradicals: Structure, properties and reactivity” (GRK2112). M.K., G.L., V.D., and A.S. acknowledge EU H2020 for funding through the Grant SEPOMO (Marie Skłodowska‐Curie Grant Agreement 722651). Computational resources were provided by the Consortium des Équipements de Calcul Intensif (CÉCI), funded by the Fonds de la Recherche Scientifiques de Belgique (F.R.S.‐FNRS) under grant no. 2.5020.11, as well as the Tier‐1 supercomputer of the Fedération Wallonie‐Bruxelles, infrastructure funded by the Walloon Region under grant agreement no. 1117545. G.L. and Y.O. acknowledge funding by the Fonds de la Recherche Scientifique‐FNRS under grant no. F.4534.21 (MIS‐IMAGINE). A.J.G. thanks the Leverhulme Trust for an Early Career Fellowship (ECF‐2022‐445). J.G. acknowledges support from the EPSRC (EP/W017091/1). The authors thank David Beljonne for fruitful discussion.
Funding Information:
J.G., V.D., and A.S. acknowledge support by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) within the Research Training School “Molecular biradicals: Structure, properties and reactivity” (GRK2112). M.K., G.L., V.D., and A.S. acknowledge EU H2020 for funding through the Grant SEPOMO (Marie Skłodowska-Curie Grant Agreement 722651). Computational resources were provided by the Consortium des Équipements de Calcul Intensif (CÉCI), funded by the Fonds de la Recherche Scientifiques de Belgique (F.R.S.-FNRS) under grant no. 2.5020.11, as well as the Tier-1 supercomputer of the Fedération Wallonie-Bruxelles, infrastructure funded by the Walloon Region under grant agreement no. 1117545. G.L. and Y.O. acknowledge funding by the Fonds de la Recherche Scientifique-FNRS under grant no. F.4534.21 (MIS-IMAGINE). A.J.G. thanks the Leverhulme Trust for an Early Career Fellowship (ECF-2022-445). J.G. acknowledges support from the EPSRC (EP/W017091/1). The authors thank David Beljonne for fruitful discussion. Open access funding enabled and organized by Projekt DEAL.
Publisher Copyright:
© 2023 The Authors. Advanced Functional Materials published by Wiley-VCH GmbH.
PY - 2023/3/16
Y1 - 2023/3/16
N2 - The great progress in organic photovoltaics (OPV) over the past few years has been largely achieved by the development of non-fullerene acceptors (NFAs), with power conversion efficiencies now approaching 20%. To further improve device performance, loss mechanisms must be identified and minimized. Triplet states are known to adversely affect device performance, since they can form energetically trapped excitons on low-lying states that are responsible for non-radiative losses or even device degradation. Halogenation of OPV materials has long been employed to tailor energy levels and to enhance open circuit voltage. Yet, the influence on recombination to triplet excitons has been largely unexplored. Using the complementary spin-sensitive methods of photoluminescence detected magnetic resonance and transient electron paramagnetic resonance corroborated by transient absorption and quantum-chemical calculations, exciton pathways in OPV blends are unravelled employing the polymer donors PBDB-T, PM6, and PM7 together with NFAs Y6 and Y7. All blends reveal triplet excitons on the NFA populated via non-geminate hole back transfer and, in blends with halogenated donors, also by spin-orbit coupling driven intersystem crossing. Identifying these triplet formation pathways in all tested solar cell absorber films highlights the untapped potential for improved charge generation to further increase plateauing OPV efficiencies.
AB - The great progress in organic photovoltaics (OPV) over the past few years has been largely achieved by the development of non-fullerene acceptors (NFAs), with power conversion efficiencies now approaching 20%. To further improve device performance, loss mechanisms must be identified and minimized. Triplet states are known to adversely affect device performance, since they can form energetically trapped excitons on low-lying states that are responsible for non-radiative losses or even device degradation. Halogenation of OPV materials has long been employed to tailor energy levels and to enhance open circuit voltage. Yet, the influence on recombination to triplet excitons has been largely unexplored. Using the complementary spin-sensitive methods of photoluminescence detected magnetic resonance and transient electron paramagnetic resonance corroborated by transient absorption and quantum-chemical calculations, exciton pathways in OPV blends are unravelled employing the polymer donors PBDB-T, PM6, and PM7 together with NFAs Y6 and Y7. All blends reveal triplet excitons on the NFA populated via non-geminate hole back transfer and, in blends with halogenated donors, also by spin-orbit coupling driven intersystem crossing. Identifying these triplet formation pathways in all tested solar cell absorber films highlights the untapped potential for improved charge generation to further increase plateauing OPV efficiencies.
KW - halogenation
KW - non-fullerene acceptors
KW - organic photovoltaics
KW - spin physics
KW - triplet excitons
UR - http://www.scopus.com/inward/record.url?scp=85146447808&partnerID=8YFLogxK
U2 - 10.1002/adfm.202212640
DO - 10.1002/adfm.202212640
M3 - Article
AN - SCOPUS:85146447808
SN - 1616-301X
VL - 33
JO - Advanced functional materials
JF - Advanced functional materials
IS - 12
M1 - 2212640
ER -