Two thermally cross‐linkable hole transport polymers that contain phenoxazine and triphenylamine moieties, X‐P1 and X‐P2, are developed for use in solution‐processed multi‐stack organic light‐emitting diodes (OLEDs). Both X‐P1 and X‐P2 exhibit satisfactory cross‐linking and optoelectronic properties. The highest occupied molecular orbital (HOMO) levels of X‐P1 and X‐P2 are ?5.24 and ?5.16 eV, respectively. Solution‐processed super yellow polymer devices (ITO/X‐P1 or X‐P2/PDY‐132/LiF/Al) with X‐P1 or X‐P2 hole transport layers of various thicknesses are fabricated with the aim of optimizing the device characteristics. The fabricated multi‐stack yellow devices containing the newly synthesized hole transport polymers exhibit satisfactory currents and power efficiencies. The optimized X‐P2 device exhibits a device efficiency that is dramatically improved by more than 66% over that of a reference device without an HTL.
