On the complex refractive index of polymer:fullerene photovoltaic blends
Journal article, 2014

We present a detailed investigation of the refractive index of polymer:fullerene blends for photovoltaic applications. The donor polymers poly[2,7-(9,9-dioctylfluorene)-alt-5,5-(4,7-di-2-thienyl-2,1,3-benzothiadiazole)] (APFO3), poly[2,3-bis-(3-octyloxyphenyl)quinoxaline-5,8-diyl-alt-thiophene-2,5-diyl] (TQ1), and poly[2,7-(9,9-dioctylfluorene)-alt-5,5-(5,10-di-2-thienyl-2,3,7,8-tetraphenyl-pyrazino[2,3-g]quinoxaline)] (APFO-Green9) were blended with either [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) or [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM). We measured variable angle spectroscopic ellipsometry for three systems, namely APFO3:PCBM, TQ1:PC71BM and APFO-Green9:PC71BM, as a function of composition and analyze the data employing a number of models. We found that Bruggeman effective medium approximations (EMA) are not precise for the description of the optical properties of these blends. This is due to a number of reasons. First, we find that there are energy shifts associated to changes in conjugation length that cannot be accounted for using EMA. Second, blending results in a strong reduction of anisotropy. Finally, our data suggest that there is some degree of vertical segregation between components. Therefore, our results support the idea that the optical properties of polymer:fullerene mixtures should be treated as alloys rather than non-interacting blends.

Author

M. Campoy-Quiles

Institute of Material Science of Barcelona (ICMAB)

Christian Müller

Chalmers, Chemical and Biological Engineering, Polymer Technology

M. Garriga

Institute of Material Science of Barcelona (ICMAB)

Ergang Wang

Chalmers, Chemical and Biological Engineering, Polymer Technology

Olle Inganäs

Linköping University

Isabel Alonso

Institute of Material Science of Barcelona (ICMAB)

Thin Solid Films

0040-6090 (ISSN)

Vol. 571 P3 371-376

Subject Categories

Polymer Chemistry

Materials Chemistry

Areas of Advance

Nanoscience and Nanotechnology (2010-2017)

Energy

Materials Science

DOI

10.1016/j.tsf.2014.02.096

More information

Latest update

2/28/2018