Dissociation of charge transfer states and carriers separation in bilayer organic solar cells - A time-resolved electroabsorption spectroscopy study

• Published in: Journal of the American Chemical Society (ISSN: 1520-5126), vol. 137, p. 8192-8198
• Washington: Amer Chemical Soc, 2015

Ultrafast optical probing of the electric field by means of Stark effect in planar heterojunction cyanine dye / fullerene organic solar cells enables to directly monitor the dynamics of free electron formation during the dissociation of interfacial charge transfer (CT) states. Motions of electrons and holes is scrutinized separately by selectively probing the Stark shift dynamics at selected wavelengths. It is shown that only charge pairs with an effective electron-hole separation distance of less than 4 nm are created during the dissociation of Frenkel excitons. Dissociation of the Coulombically bound charge pairs is identified as the major rate-limiting step for charge carriers’ generation. Interfacial CT states split into free charges on the time-scale of tens to hundreds of picoseconds, mainly by electron escape from the Coulomb potential over a barrier that is lowered by the electric field. The motion of holes in the small molecule donor material during the charge separation time is found to be insignificant.

Keywords: Organic photovoltaics ; Planar heterojunctions ; Charge transfer ; Ultrafast ; Electroabsorption

Reference

• EPFL-ARTICLE-208792
• doi:10.1021/jacs.5b03682
• View record in Web of Science

Record created on 2015-06-04, modified on 2017-05-12