A thermally cross-linked hole-transporting film with the remarkable solvent resistance for solution-processed OLEDs

In this work, we report a systematic study of the properties of the thermal cross-linkable triarylamine based hole-transporting material (HTM) N,N'-di-p-tolyl-N,N'-bis(4-vinylphenyl)-[1,1'-biphenyl]-4,4'-diamine (V-p-TPD) and the distinctive nature of its cross-linked thin films fabricated by solution process under mild thermal polymerization without any initiator. The cross-linked V-p-TPD film exhibited remarkable solution resistance to common solute such as chlorobenzene, toluene, chloroform and tetrahydrofuran. The cross-linked V-p-TPD film showed better morphological stability than vacuum-deposited film of its monomer TPD. The space-charge-limited current (SCLC) measurements revealed that the cross-linked V-p-TPD film afforded comparable hole mobility with vacuum-deposited TPD film. Finally, we applied the cross-linked V-p-TPD film in organic light-emitting diodes (OLEDs) to evaluate its performance in all-solution-processed OLEDs.