X-ray microscopic investigation of molecular orientation in a hole carrier thin film for organic solar cells

As dipyranylidenes are excellent hole carriers, applications in organic solar cells or organic light emitting diode are envisaged. In the present study, we investigate the morphology of 2,2',6,6'-tetraphenyl-4,4'-dipyranylidene (DIPO-Ph-4) deposited under vacuum on a silicon nitride (Si3N4) substrate, a paradigmatic system for the study of molecular crystal/inorganic substrate interfaces. Samples with various coating ratios and different thermal treatments were prepared. The films were characterized by atomic force microscopy and scanning transmission X-ray microscopy to gain insight into material growth. The results show a change in orientation at a molecular level depending upon the evaporation conditions. We are now able to tailor an organic layer with a specific molecular orientation and a specific electronic behavior.