Novel carbazole-acridine-based hole transport polymer for low turn-on voltage of green quantum dot light-emitting diodes

Herein, a novel hole transport polymer, P-CzAc, for solution-processed green quantum dot light-emitting diodes (QD-LEDs) was synthesized. P-CzAc consists of a polystyrene backbone and 10-(9H-carbazol-3-yl)-9,9-dimethyl-9,10-dihydroacridine as side-chain pendants. The design strategy aims to improve the hole transportability and achieve the low-lying highest occupied molecular orbital (HOMO) level for P-CzAc for reducing the charge injection barrier from the hole injection layer to the hole transport layer. P-CzAc showed good solubility in tetrahydrofuran, methylene chloride, and aromatic solvents, but high solvent tolerance for hexane and octane, similar to poly(N-vinylcarbazole) (PVK). Compared to PVK (HOMO = −5.58 eV), P-CzAc exhibited a relatively high-lying HOMO level of −5.33 eV. In particular, the hole mobility (μh) of P-CzAc was estimated to be 2.24 × 10−6 cm2 V−1 s−1, which is much higher than that of PVK (μh = 4.11 × 10−9 cm2 V−1 s−1). In solution-processed green QD-LEDs, the P-CzAc-based device exhibited a relatively low turn-on voltage (Von) of 2.8 V and a high maximum external quantum efficiency (EQE) of 11.6%. In comparison with a PVK-based device (Von = 4.4 V; EQE = 8.6%), the P-CzAc-based device is more efficient owing to the significant improvement in hole injection.