THERMALLY-INDUCED FAILURE MECHANISMS OF ORGANIC LIGHT-EMITTING DEVICESTRUCTURES PROBED BY X-RAY SPECULAR REFLECTIVITY

The thermal evolution of organic light emitting device structures and materials has been measured using X-ray specular reflectivity. Thermal ly induced failure of these structures is found to be due to the large thermal expansion of the hole transport layer (N,N'-diphenyl-N,N'-bis (3-methylphenyl)1, 1'-biphenyl-4,4'diamine, or TPD) associated with it s low glass transition temperature, suggesting a strain-driven failure mechanism (as opposed to TPD recrystallization). These results sugges t the possibility of optimizing organic light emitting devices through direct in-situ measurements of their structure and stability. (C) 199 7 Elsevier Science B.V.