Assessing the effects of increasing conjugation length on exciton diffusion: from small molecules to the polymeric limit

Leonardo Evaristo de Sousa, Laura Simonassi Raso de Paiva, Demetrio Antonio da Silva Filho*, Gjergji Sini, Pedro Henrique de Oliveira Neto

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review


Organic solar cells (OSC) generally contain long-chain pi-conjugated polymers as donor materials, but, more recently, small-molecule donors have also attracted considerable attention. The nature of these compounds is of crucial importance concerning the various processes that determine device performance, among which singlet exciton diffusion is one of the most relevant. The efficiency of the diffusion mechanism depends on several aspects, from system morphology to electronic structure properties, which vary importantly with molecular size. In this work, we investigated the effects of conjugation length on the exciton diffusion length through electronic structure calculations and an exciton diffusion model. By applying extrapolation procedures to thiophene and phenylene vinylene oligomer series, we investigate their electronic and optical properties from the small-molecule point of view to the polymeric limit. Several properties are calculated as a function of oligomer size, including transition energies, absorption and emission spectra, reorganization energies, exciton coupling and Forster radii. Finally, an exciton diffusion model is used to estimate diffusion lengths as a function of oligomer size and for the polymeric limit showing agreement with experimental data. Results also show that longer conjugation lengths correlate with longer exciton diffusion lengths in spite of also being associated with shorter exciton lifetimes.
Original languageEnglish
JournalPhysical Chemistry Chemical Physics
Issue number29
Pages (from-to)15635-15644
Number of pages10
Publication statusPublished - 2021


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