Effect of surface treatment and functionalization on the ITO properties for OLEDs

The relation between ITO morphology and surface properties has been studied by wettability measurements and AFM microscopy. Different wet cleaning procedures have been investigated leading to different surface properties: ultrasonic degreasing, RCA and Aqua regia treatment. After full elimination of the organic surface contaminants, the ITO surface shows a main basic surface component. RCA and Aqua regia treatments are the most efficient techniques for cleaning ITO surfaces from organic contamination. Nevertheless, Aqua regia treatment induces ITO surface degradation, which is evidenced by AFM observations and resistance sheet measurements. The ITO surface has been derivatized with a SAM layer of phosphonic acid to improve the ITO/polymer interface. Effect of 2-chloroethylphosphonic acid layer on the different components of the surface energy was determined: acid component is increased whereas basic component is decreased, showing the good coverage of the ITO surface by the SAM layer. A more compact coating of POMX polymer is obtained after SAM functionalization of ITO samples cleaned with RCA treatment.