Evolution of the characterization of horizontally aligned organic light‐emitting molecules and their recent progress of molecular design

Abstract This review article surveys the organic small molecular materials, light‐emitting for most of them, being studied for the molecular alignment or orientation in thin films. Following a chronicle order, three practical characterization techniques, variable angle spectroscopic ellipsometry (VASE), angle‐dependent photoluminescence (ADPL), and grazing incidence wide‐angle x‐ray scattering (GIWAXS) have been used to probe phosphorescence, thermally activated delayed fluorescence (TADF) materials, as well as those of non‐phosphorescence and non‐TADF materials.