The polymer TQ1, (poly[2,3-bis-(3-octyloxyphenyl)quinoxaline-5,8-diyl-alt-thiophene-2,5-diyl]) [1], exhibits a low band gap, approximately 2.4 eV, and is a popular candidate as donor in organic solar cells. A suitable acceptor molecule together with TQ1 is [6,6]-phenyl-C71-butyric acid methyl ester (PC70BM) [1].
We have studied films of TQ1, with and without PC70BM, spin-casted from different solvents by fluorescence spectroscopy. The solvents used in this study were chloroform (CF), chlorobenzene (CB), and o-dichlorobenzene (ODCB), while 1-chloronaphthalene (1CN) was used as solvent additive. From a spectroscopic point of view, TQ1 acts as fluorescent probe and PC71BM as quencher.
Vertical phase-separation occurs in the blend films and the surface composition depends on the solvent used. All films are polymer-enriched at the surface, and 1CN strengthens this tendency. These morphological differences cause alterations in the fluorescence from TQ1. The degree of quenching is coupled to the morphology through the distance between TQ1 and PC70BM in the film.
The results show that fluorescence spectroscopy can be used as a complementary technique to investigate organic blend film compositions with high sensitivity.
Reference
1. Wang E, Hou L, Wang Z, Hellström S, Zhang F, Inganäs O, Andersson MR, Adv. Mater., 22, 2010, 5240-44
Jan.van.Stam@kau.se
