POLYMER LIGHT EMITTING DIODES

Abstract

Light emitting diodes using conjugated polymers such as poly(p-phenylene vinylene) [PPV] and poly(2-methoxy-5-(2'-ethyl hexyloxy)-1,4-phenylene vinylene) [MEHPPV]have been successfully fabricated. The surface of PPV has been activated by argon and oxygen plasma prior to evaporation of the aluminium cathode. The characteristics of pristine and plasma treated devices have been compared. Angle-resolved X-ray photoelectron spectroscopy (XPS) measurements have been used to characterize the surface compositions of the pristine and plasma treated PPV surfaces. The stability of MEH-PPV to thermal, irradiative and X-ray stresses have been measured. The changes if any were monitored by UV-VIS spectroscopy, FT-IR spectroscopy and XPS. It was observed that negligible degradation of MEH-PPV occurred when it was irradiated in an inert atmosphere compared to ambient atmosphere. X-ray was found to make the polymer insoluble and the orange-red color changed to light yellow. The surface of MEH-PPV was treated with argon, oxygen and nitrogen plasma and the development of new functionalities on the surface were monitored by XPS. The in-situ evaporation of aluminium and indium followed by XPS analysis of the PPV surface has been performed to characterize the metal-polymer interface as it forms. This interface study attempts to elucidate the formation of the metal-on-polymer (MOP) interface and detect the formation of new functional groups at the interface if any.