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Your search keyword '"Londi G"' showing total 2 results
Start Over Author "Londi G" Topic condensed matter - materials science
2 results on '"Londi G"'

1. Structural order promotes efficient separation of delocalized charges at molecular heterojunctions

Author

Jia, Xiangkun, Soprani, Lorenzo, Londi, Giacomo, Hosseini, Seyed Mehrdad, Talnack, Felix, Mannsfeld, Stefan, Shoaee, Safa, Neher, Dieter, Reineke, Sebastian, Muccioli, Luca, D'Avino, Gabriele, Vandewal, Koen, Beljonne, David, Jia, Donato Spoltore X., Reineke, S., Soprani, L., Muccioli, L., Londi, G., Beljonne, D., Hosseini, S. M., Shoaee, S., Neher, D., Talnack, F., Mannsfeld, S., D'Avino, G., Vandewal, K., and Spoltore, D.

Subjects
Physics - Applied Physics, Condensed Matter - Materials Science
Abstract

The energetic landscape at the interface between electron donating and accepting molecular materials favors efficient conversion of intermolecular charge-transfer states (CTS) into free charge carriers in high-performance organic solar cells. Here, we elucidate how interfacial energetics, charge generation and radiative recombination are affected by structural ordering. We experimentally determine the CTS binding energy of a series of model, small molecule donor-acceptor blends, where the used acceptors (B2PYMPM, B3PYMPM and B4PYMPM) differ only in the nitrogen position of their lateral pyridine rings. We find that the formation of an ordered, face-on molecular packing in B4PYMPM is beneficial to efficient, field-independent charge separation, leading to fill factors over 70% in photovoltaic devices. This is rationalized by a comprehensive computational protocol showing that, compared to the more amorphous and isotropically oriented B2PYMPM, the higher order of the B4PYMPM molecules provides more delocalized CTS. Furthermore, we find no correlation between the quantum efficiency of radiative free charge carrier recombination and the bound or unbound nature of the CTS. This work highlights the importance of structural ordering at donor-acceptor interfaces for efficient free carrier generation and shows that more ordering and less bound CT states do not preclude efficient radiative recombination.

Published
2022

2. Triplet Excitons and Associated Efficiency‐Limiting Pathways in Organic Solar Cell Blends Based on (Non‐) Halogenated PBDB‐T and Y‐Series

Author

Grüne, J, Londi, G, Gillett, AJ, Stähly, B, Lulei, S, Kotova, M, Olivier, Y, Dyakonov, V, Sperlich, A, Grüne, J [0000-0003-3579-0455], Londi, G [0000-0001-7777-9161], Gillett, AJ [0000-0001-7572-7333], Olivier, Y [0000-0003-2193-1536], Dyakonov, V [0000-0001-8725-9573], Sperlich, A [0000-0002-0850-6757], and Apollo - University of Cambridge Repository

Subjects
Chemical Physics (physics.chem-ph), Condensed Matter - Materials Science, Materials Science (cond-mat.mtrl-sci), FOS: Physical sciences, triplet excitons, Condensed Matter Physics, Electronic, Optical and Magnetic Materials, Biomaterials, halogenation, Physics - Chemical Physics, non-fullerene acceptors, Electrochemistry, spin physics, ddc:530, organic photovoltaics
Abstract

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 (PLDMR) and transient electron paramagnetic resonance (trEPR) corroborated by transient absorption and quantum-chemical calculations, we unravel exciton pathways in OPV blends 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., Comment: 43 pages, 25 figures

Published
2023

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