Molecular Orientation in Polymer Films for Organic Solar Cells Studied by NEXAFS

Abstract

The application of new polymer materials for organic solar cells requires a detailed understanding of the orientation and the electronic properties of the system because these have a dramatic effect on the device performance and efficiency. The films were prepared by doctor blade casting, a simple preparation route from solution. We study the orientation of the low band gap polymers poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b:3,4-b′]dithiophene)-alt-4,7(2,1,3-benzothiadiazole)] (PCPDTBT) and poly-[2,6-(4,4-bis(2-ethyl)-4H-cyclopenta[2,1-b:3,4-b′]dithiophene)-alt-5,8-(2,3-dioctylquinoxaline)] (PCPDTQ) as well as of the state of the art polymer poly(3-hexyl-thiophene) (P3HT) using near-edge X-ray absorption fine structure spectroscopy (NEXAFS). Clear angular dependence in the NEXAFS spectra is observed for P3HT and PCPDTBT pointing to well-orientated films.