Rigorous Determination of Dipole Orientation in Organic Thin Films Using Angle-Dependent Photoluminescence

The orientation of transition dipole moments (TDMs) in an emitter layer (EML) is a critical factor that directly affects the outcoupling efficiency of organic light-emitting diodes. Although angle-dependent photoluminescence (PL) systems are often used for the characterization and analysis of such TDM orientation information, most studies have assumed that the transition dipoles in an EML are not spatially distributed but confined within an extremely narrow region, which could result in a biased interpretation of the measured data. In this letter, we theoretically and experimentally reveal that the spatial distribution of transition dipoles should be rigorously considered in angle-dependent PL systems, especially for thick EMLs, and that the conventional assumption might be valid only under limited conditions.