Phthalimide-Based Transparent Electron-Transport Materials with Oriented-Amorphous Structures: Preparation from Solution-Processed Precursor Films

A star-shaped molecule featuring three phthalimide units attached to a triazine core was designed as an electron-transport material. Solution processing was achieved by preparing a precursor molecule bearing tert-butoxycarbonyl (Boc) substituents, which are afterwards removed by annealing. The annealed film is transparent to visible light, with an absorption edge of 339 nm. Two-dimensional grazing incidence X-ray diffraction (2D-GIXD) and p-polarized multiple-angle incidence resolution spectrometry (pMAIRS) measurements showed that the molecular orientation changed from random to face-on during the cleaving of Boc groups while keeping the overall crystallinity low. This "oriented-amorphous" structure is desirable for transport layers in devices such as organic light-emitting diodes (OLEDs) and solar cells.