In this study, we evaluated the degradation mechanism in quantum dot light-emitting diodes (QLEDs) to improve the device lifetime. We measured the hole mobility using the delay time of transient electroluminescence for three types of hole transport layer (HTL) materials. In addition, we estimated the degradation of luminance efficiency and hole mobility under constant current drive. As a result, the HTL material with a higher hole mobility yielded longer QLED device lifetimes. Through substitution of the HTL material from poly (9-vinylcarbazole) (PVK) to poly [(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4′-(N-(4-sec-butylphenyl)diphenylamine)] (TFB), the hole mobility and the 95% luminance lifetime from initial luminance improved from 0.5 × 10−5 cm2/V⋅s and 2.90 h at J = 10 mA/cm2 to 1.1 × 10−5 cm2/V⋅s and 179 h, respectively. Moreover, we clarified that the degradation of the luminescent efficiency is correlated with the hole mobility.

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