Efficiency Enhancement of InP-Based Quantum Dot Light-Emitting Diodes by Introducing a Phosphorescent-Dye Sensitizer in a Hole Transport Layer

Low-toxicity indium phosphide (InP) quantum dots (QDs) have attracted considerable attention for their environmental benefits. However, compared to conventional high-performance cadmium-based QDs, InP-QDs suffer from weaker electron confinement, which leads to significant electron accumulation and nonradiative recombination in InP-based quantum dot light-emitting diodes (InP-QLEDs). In this work, we propose introducing the sensitizer as the external exciton recombination center within a hole transport layer (HTL). This sensitizer harvests accumulated electrons to form excitons and transfers energy to adjacent InP-QDs, thereby enhancing radiative recombination. To demonstrate this approach, we fabricated red InP-QLEDs with a sensitizer-doped HTL composed of poly(9,9-dioctylfluorene-alt-N-(4-s-butylphenyl)-diphenylamine) and tris[2-(p-tolyl)pyridine]iridium(III). Our results show that the introduction of the sensitizer promotes carrier-balanced injection through interfacial modification and enhances radiative recombination by collecting accumulated electrons. Together, these effects significantly improve the performance of InP-QLEDs. The maximum external quantum efficiency of the InP-QLEDs increases from 8.3 to 17.1% with a doped HTL. Moreover, the operational lifetime of the device with the sensitizer is extended by 17.6-fold. Our findings demonstrate that introducing a phosphorescent-dye sensitizer in a transporting layer is a simple and effective strategy to achieve high-performance InP-QLEDs.