How the Size and Density of Charge-Transfer Excitons Depend on Heterojunction's Architecture

Autor(es)

Varella, Marcio T. do N. ^[1] ; Stojanovic, Ljiljana ^[2] ; Vuong, Van Quan ; Irle, Stephan ^{[3, 4]} ; Niehaus, Thomas A. ^[5] ; Barbatti, Mario ^[6]

Afiliação do(s) autor(es)

^[1] Univ Sao Paulo, Inst Fis, BR-05508090 Sao Paulo, SP - Brazil

^[2] Queen Mary Univ London, Sch Biol & Chem Sci, London E1 4NS - England

^[3] Van Quan Vuong, Univ Tennessee, Bredesen Ctr Interdisciplinary Res & Grad Educ, Knoxville, TN 37996 - USA

^[4] Oak Ridge Natl Lab, Computat Sci & Engn Div, POB 2009, Oak Ridge, TN 37831 - USA

^[5] Univ Claude Bernard Lyon 1, Inst Lumiere Matiere, CNRS, Univ Lyon, F-69622 Villeurbanne - France

^[6] Aix Marseille Univ, CNRS, ICR, Marseille - France

• Tipo de documento: Artigo Científico
• Fonte: Journal of Physical Chemistry C; v. 125, n. 10, p. 5458-5474, MAR 18 2021.
• Citações Web of Science: 0

Resumo

We have characterized the size, intensity, density, and distribution of charge-transfer (CT) excitons as a function of the acceptor-donor architecture of prototypical organic interfaces. This characterization was done by computational analysis of 17 models of varying numbers, positions, and orientations of the donor and acceptor molecules. The models' building blocks were phenyl-C-61-butyric acid methyl ester (PCBM) fullerene acceptors and dual-band donor polymers composed of thiophene, benzothiadiazole, and benzotriazole subunits. The electronic structure of the donor-acceptor complexes was computed with the time-dependent long-range-corrected density-functional tight-binding method and analyzed with the fragment-based one-electron transition density matrix. In all models, the complexes with edge-on orientation have denser spectra of low-energy CT states lying below the absorption bands compared to the complexes with face-on orientation. This CT-state distribution in edge-on complexes provides a gate to efficiently populate cold CT excitons. Moreover, the cold CT excitons have a higher degree of charge separation in the edge-on than in the face-on complexes. The CT amount and the CT exciton size generally increase with the energy of the CT states, although the electron remains localized on a single molecule in cold CT states. Delocalization over two PCBM molecules was observed for high-energy CT states. The exciton size also depends on the orientation. Larger excitons are produced by the delocalization of the electrons perpendicularly to the interface. When the delocalization is parallel, the smaller electron-hole distances yield moderately sized CT excitons. (AU)

• Processo FAPESP: 18/22948-0 - Modelos Moleculares para Fotovoltaica Orgânica
• Beneficiário: Márcio Teixeira do Nascimento Varella
• Modalidade de apoio: Bolsas no Exterior - Pesquisa