Trade-Offs between Illumination and Modulation Performances of Quantum-Dot LED

We investigate the effects of the hole transport layer (HTL) and the buffer layer in a CdSe/ZnS quantum-dot LED (QLED) to reveal several important performance trade-offs in the QLED design. Our fabricated QLED samples show that, among the three common HTL materials, poly(9-vinlycarbazole) (PVK), poly[N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)-benzidine] (poly-TPD), and poly(9,9-dioctylfluorene-co-N-(4-(3-methylpropyl)) diphenylamine) (TFB), PVK provides the highest luminance of 1.0× 10⁵ cd/m², but the smallest modulation bandwidth of 2.0 MHz, while TFB provides the lowest luminance of 5.8× 10⁴ cd/m², but the largest bandwidth of 6.5 MHz. For each HTL material, there exists an optimal HTL thickness for the illumination performance, but the bandwidth decreases with an increase in the HTL thickness. The incorporation of a LiF buffer layer in a QLED can significantly increase the luminance, but at the expense of the modulation bandwidth. Our results are useful for the design of QLEDs for visible light communication applications.