Photoemission studies of band alignment in oligothiophene/oligophenyl based devices

UV photocmission has been used to study band alignment at the interfaces of metal / organic / ITO model devices based on phenyl and thiophene oligomers. Although Al is the most commonly used metal contact, we show that band alignment in clean Al / oligomer / ITO devices is, in fact, extremely sub-optimal. Not only do Al and ITO have similar work functions, but the interaction of these organics with both surfaces is of the same form, leading to near identical alignment at both interfaces. The situation, however, can be greatly improved by interface modification e.g. changing the contact metal, or adding controlled amounts of oxygen.