Probing component segregation and anisotropy for co-deposited glasses of TCTA and Ir(ppy)3 by GIWAXS

Abstract

Vapor-deposited glasses of organic semiconductors are frequently used as active layers for organic luminescence devices, such as organic light-emitting diodes. Although it is well known that the aggregation of dopants is a significant factor determining device performance and lifetime, information about the dispersion of the dopants has usually been obtained indirectly using techniques such as photoluminescence spectra. In this work, we use grazing incidence wide-angle x-ray scattering (GIWAXS) to directly probe component segregation in co-deposited glasses of TCTA and Ir(ppy)3, a popular light emitter, across the wide range of compositions and substrate temperatures. As a complementary tool, differential scanning calorimetry and spectroscopic ellipsometry were utilized to further probe segregation and anisotropy of co-deposited glasses. We find that component segregation is observed in the vapor-deposited glasses, at all compositions we studied [10%, 30%, and 50% of Ir(ppy)3 concentration], as identified by an anisotropic scattering peak, resulting from clusters of periodically arranged Ir(ppy)3 molecules. As a result, this paper provides a novel route to probe component segregation in co-deposited glasses by GIWAXS.