A contact forming phenomenon between a variety of metal contacts and organic charge transport layers has been previously reported whereby the hole injection efficiency of the contacts evolves from blocking to ohmic over time periods of up to 1 month. Two main processes, one slow and one rapid, were found to govern the injection evolution by using an experimental technique that combines field-dependent injection current measurements with time-of-flight drift mobility measurements on the same films. Results regarding the rapid process (1-3 hours) are now presented for a variety of organic interfaces, including a molecularly doped polymer of triarylamine (TPD) in polycarbonate, evaporated TPD films and films of the electroluminescent polymer MEH-PPV. The process occurs with evaporated metal contacts, with metal substrates and with liquid Hg, ie. independantly of the contact fabrication method. Variations of the intermolecular structure by organic surface treatment and by the use of sterically hindered TPD isomers suggest a reorganization at the organic surface on interface formation.
Andronique Ioannidis, John S. Facci, Martin A. Abkowitz, "Short-term evolution of injection efficiency at metal/organic interfaces" in Proc. IS&T Int'l Conf. on Digital Printing Technologies (NIP15), 1999, pp 739 - 742, https://doi.org/10.2352/ISSN.2169-4451.1999.15.1.art00093_2