Tailoring Molecular Ordering and Energy Levels via Solvent Selection for Inverted QLEDs with Dual PVK Hole Transport Layers

Abstract In inverted quantum dot light‐emitting diodes (QLEDs), the energy barrier for holes from the anode is significantly larger than that for electrons from the cathode. This barrier disparity is a major challenge, leading to low efficiency in inverted QLEDs. To address this issue, dual hole transport layers (HTLs) made of the same material, poly(N‐vinyl carbazole) (PVK), but with different molecular assembly structures are introduced. These structures are achieved using two solvents with a large boiling‐point gap: 1,4‐dioxane (1,4‐D) and gamma‐valerolactone (GVL). The PVK film fabricated using GVL with a higher boiling point exhibits better‐ordered and denser molecular assembly compared to that fabricated using 1,4‐D. The highest occupied molecular orbital levels of the two PVK layers are stepwise, attributed to their distinct molecular assembly structures. Consequently, a device with dual HTLs demonstrates over 40% improvement in external quantum efficiency and power efficiency compared to a device with a single HTL. This result provides a novel approach to tuning the energy levels of functional layers in QLEDs, significantly enhancing device performance.