Highly efficient and negligible efficiency roll-off non-doped blue electroluminescence with a synergistic effect of fast-balanced carrier transport and appropriate hybridized excited states

The most critical scientific problem for efficient blue emitters is to solve the inherent contradiction between wide bandgap characteristics and difficult carrier injection/unbalanced transmission. Herein, three donor-π-acceptor (D-π-A) type blue materials (TPACFTAZ, 9PCZCFTAZ, and 3PCZCFTAZ) based on fluorene-bridged and triazine acceptors were designed and synthesized. By regulating the donor strength and substitution sites, the synergistic optimization of solid-state aggregation mode and excited state characteristics has been achieved. Single crystal analysis shows that 3PCZCFTAZ exhibits the most abundant and effective intermolecular forces, obtaining fast-balanced carrier transport with electron and hole transport rates of 10.60 × 10^-5 cm² V^-1 s^-1 and 9.53 × 10^-5 cm² V^-1 s^-1, respectively. Moreover, 3PCZCFTAZ also accomplished sufficient and stable hybridization between localized excited (LE) and charge transfer (CT) states, with a solid-state photoluminescence quantum yield (PLQY) of 71.2% and exciton utilization efficiency (EUE) of 82.2%. More importantly, the non-doped device based on 3PCZCFTAZ achieved a high EQE of 11.7%, with an efficiency roll-off of 0 @1000 cd m^-2. Among similar non-doped devices, this device exhibits not only negligible efficiency roll-off at high brightness, but also ranks among the most efficient reported to date.