The goal of our HEiKA project was to find electron transport layer (ETL) materials suitable for multi-layer OLEDs according to the orthogonal solvent concept. Therefore, the material needs to be soluble in some solvents and insoluble in others. This is to prevent solvent penetration in a layer below and layer intermixing.
Tetraazapentazenes (TAPs) are electron-poor derivatives compared to the well-studied pentacene. The TAPs shows a lower lying LUMO energy level (ca. -3.5 eV) and are applicable as electron-transport materials (ETM). We adjust optical properties of mono-bromo TAP by chemical functionalization. We received a high amount of new compounds that are now under investigation. With the synthesized materials mass transport measurements are done using an ultraprecise sorption apparatus with a quartz crystal microbalance. The measurements show that it is possible to tune solubility by adding substituents and get ETL materials that fit the orthogonal solvent concept. Also we found a material/solvent combination with a profoundly increased solvent diffusion coefficient.