PIN quantum-dot LEDs with enhanced efficiency and stability enabled by bulk-heterojunction hole transport layer

Although quantum-dot light-emitting diodes (QLEDs) can exhibit high efficiency and long lifetime, the realization of QLEDs-based displays remains challenging due to their complex multilayer architectures and the use of unstable poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) hole injection layer (HIL). Here, we develop a novel trilayer p-type/intrinsic/n-type (PIN) QLED with only three functional layers: PTAA:TFB:F4-TCNQ (PTAA: poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine]; TFB: poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4'-(N-(4-sec-butylphenyl)diphenylamine)]; F4-TCNQ: 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane) bulk-heterojunction (BHJ) hole transport layer (HTL), quantum-dot emitting layer, and ZnMgO electron transport layer. Due to well-matched energy level, increased hole transport path from PTAA to TFB, and improved hole density and enhanced hole mobility of the PTAA:TFB:F4-TCNQ BHJ HTL, the resultant trilayer PIN QLED exhibits a high external quantum efficiency (EQE) of 25.1% and an impressive peak brightness of 382,600 cd/m², which are significantly higher than those of the control QLED. Moreover, the trilayer PIN QLED also shows a 1.94-fold longer operational lifetime than control QLED due to the improved device performance, reduced charge accumulation, and removal of unstable PEDOT:PSS. The developed trilayer PIN QLED, with fewer functional layers and better stability, could promote the practical application of QLED in displays and solid-state lighting.