Manipulating Carrier Recombination Dynamics Through Rational Dual-Trap Engineering in Exciplex Heterojunction for High-Performance OLEDs.

Abstract

While trap states are traditionally considered as performance-limiting defects in organic light-emitting diodes (OLEDs), this work presents a dual-trap exciplex heterojunction system that strategically engineers trap states to enhance device performance. The tailored electron (4CzTPNBu in p-type host) and hole (PO-01 in n-type host) traps are employed for interfacial bidirectional carrier capture synergistically without compromising carrier transport in the exciplex heterojunction system. This innovative design converts interfacial traps into immediate radiative trap-assisted recombination (TAR) centers with significant expansion of exciton recombination zone, simultaneously preventing carrier transport imbalance and charge accumulation. The yellow OLEDs demonstrate cutting-edge 33.9% external quantum efficiency (EQE), and 453.6 h operational lifetime (LT₉₀ at 1000 cd m^-2) representing a ninefold enhancement over conventional architectures. Through ideality factor analysis complemented by single-carrier device and transient electroluminescence studies, the fundamental charge transport physics and trap-mediated dynamics are unraveled. Implementation of dual-trap in narrow-band hyperfluorescent systems also enables EQEs surpassing 36% and mitigated efficiency roll-off, along with prolonged LT₉₀ of 178.7 h. The dual-trap methodology successfully merges the advantages for twin emitters and achieves a win-win scenario for efficiency and lifetime, providing a promising paradigm for future high-performance OLED development.