All-Solution-Processed Top-Emitting InP Quantum Dot Light-Emitting Diode with Polyethylenimine Interfacial Layer

Recent studies on top-emitting structure, which is designed to enhance the color purity and outcoupling efficiency of quantum-dot light-emitting diodes (QLEDs), employ commercially unviable methods owing to limited options for applying the hole injection layer through solution processes on the bottom electrode. In this study, all-solution-processable conventional top-emitting QLEDs (TQLEDs) are successfully fabricated by introducing a polyethylenimine (PEI) interlayer, doping isopropyl alcohol (IPA) into the hole-injection layer (poly (3,4-ethylenedioxythiophene):poly(4-styrenesulfonate), PEDOT:PSS), and using the dynamic spin-coating method. The increased hole injection resulting from the tuned anode-HIL interface by the PEI and IPA-doped HIL, coupled with the enhanced outcoupling efficiency and full width at half maximum (FWHM) derived from the optimized cavity length through simulation, realizes a red InP QLED with high efficiency and color purity. The optimized TQLED exhibits a maximum current efficiency and FWHM of 28.04 cd A⁻¹ and 36 nm, respectively, which are threefold higher and 8 nm narrower than those of bottom-emitting QLEDs, marking the highest current efficiency ever reported for top-emitting red InP QLEDs.