The simultaneous realization of high external quantum efficiency (EQE) and high degree of polarization (DoP) in circularly polarized light-emitting diodes (LEDs) remains a substantial challenge. Here, we present a polarization-selective photon recycling microcavity integrated into a top-emitting quantum-dot LED (TE-QLED). The device incorporates a chiral Bragg-specular reflection microcavity, in which light with the opposite handedness to the Bragg layer is transmitted directly, whereas light with the same handedness undergoes chirality reversal and exits the microcavity with the opposite handedness. This polarization-selective photon recycling mechanism enables the recovery of photons that would otherwise be lost in conventional polarized light generation, thereby overcoming the physical limit of 50% loss in polarized emission. As a result, a circularly polarized QLED with a DoP of 81% (electroluminescence dissymmetry factor g_lum(EL) = 1.62) and a high EQE of 20.27% is achieved, with only 17.8% light loss compared to the reference device. Furthermore, a proof-of-concept three-dimensional display prototype is demonstrated, highlighting the potential of this approach for advanced display technologies.

Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) thin film is widely used as a hole injection layer (HIL) in quantum-dot (QD) light-emitting diodes (LEDs). However, its acidic and hygroscopic nature erodes the indium tin oxide electrode, causing serious device stability issues. To overcome the limitations, QLEDs that utilize self-assembled molecules (SAMs) as the HILs have been proposed and demonstrated, offering both high efficiency and improved stability. The 4PADCB SAM forms a high-quality film characterized by excellent transmittance and low surface roughness. Crucially, it possesses a high work function, which facilitates effective hole injection into the QD layer, thereby improving charge balance and reducing the accumulation of excess charges within the QLED. Additionally, the 4PADCB’s shallow lowest unoccupied molecular orbital energy level prevents electron leakage towards the anode. As a result, the 4PADCB-based red QLED exhibits a maximum external quantum efficiency of 28.07%, a peak power efficiency of 37.24 lm/W, and an extended T₉₅ operational lifetime of 12,401 h at 1000 cd/m², significantly outperforming the device based on PEDOT:PSS. This SAM HIL approach paves the way towards commercially viable, high-performance QLEDs in next generation displays.

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.