Spatiotemporal mapping uncouples exciton diffusion from singlet–singlet annihilation in the electron acceptor Y6

Understanding the spatial dynamics of nanoscale exciton transport beyond the temporal decay is essential for further improvements of nanostructured optoelectronic devices, such as solar cells. The diffusion coefficient (D) of the nonfullerene electron acceptor Y6 has so far only been determined indirectly, from singlet–singlet annihilation (SSA) experiments. Here, we present the full picture of the exciton dynamics, adding the spatial domain to the temporal one, by spatiotemporally resolved photoluminescence microscopy. In this way, we directly track diffusion and we are able to decouple the real spatial broadening from its overestimation given by SSA. We measured the diffusion coefficient, D = 0.017 ± 0.003 cm2/s, which gives a Y6 film diffusion length of ¿=¿¿¿¿¿¿¿v˜35 nm. Thus, we provide an essential tool that enables a direct and free-of-artifacts determination of diffusion coefficients, which we expect to be pivotal for further studies on exciton dynamics in energy materials.

The authors acknowledge support through the MCIN/AEI projects PRE2019-091051 and PGC2018-096875-B-I00, the “Severo Ochoa” program for Centers of Excellence in R&D CEX2019-000910-S, the Catalan AGAUR 2017SGR1369, Fundació Privada Cellex, Fundació Privada Mir-Puig, and the Generalitat de Catalunya through the CERCA program. L.B. received funding from the Clean Planet Program supported by Fundació Joan Ribas Araquistain (FJRA). N.F.v.H. acknowl- edges the financial support by the European Commission (ERC Advanced Grant 670949-LightNet). J.M. and F.B. acknowledge the financial support by the European Commis- sion (951843), Spanish MINECO (MAT2017-89522-R) and MCIN/AEI (PRE2018-084881). This work was partially funded by Ministerio de Ciencia e Innovación (grant No. PID2020-112650RB-I00).

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