Electroabsorption spectroscopic study of cyano-substituted phenylene vinylene polymer (CN-PPV)

We report electroabsorption spectroscopy measurements on a single layer cyano-substituted phenylene vinylene (CN-PPV) polymer device and also contact potential difference (CPD) in the device structure ITO/PEDOT: PSS/CN-PPV/Al. The electroabsorption (EA) spectrum shows well developed structure of a peak and valley at 2.2 and 2.56 eV, respectively. It is demonstrated that the line shape more closely reflects second derivative of absorption spectra than corresponding first derivative. The origin of dominant features in EA spectra in the range of 1.5–3.2 eV are discussed qualitatively without taking recourse to fitting a linear combination of derivatives of linear absorption. The contact potential difference (CPD) measured using this technique shows a value 0.6 V that is exactly the work function difference between ITO and Al electrode used in this structure. These features in EA measurements of CN-PPV are in contrast to the ones observed in the case of PPV thin films.