Physical vapour deposition of cyanine salts and their first application in organic electronic devices

A symmetrical trimethine indocyanine dye chromophore was modified with the bistriflylimide anion to study the changes in Coulomb interactions, thermal stability and the volatility of the organic salt. The bulky bistriflylimide anion minimizes electrostatic interactions and increases the vapour pressure of the compound resulting in an increased volatility of the organic salt. First examples of entirely vacuum-processed bulk heterojunction organic photovoltaic devices show the proof of concept. We give evidence that the well dispersed negative charge of the bistriflylimide introduces quasi gas phase conditions to the cyanine chromophore. This overcomes the existing restriction of thin film formation via spincasting in cyanine dye based organic electronics and expands the thin film fabrication process choices towards physical vapour deposition.