Spatial Planarization Controls Optical Anisotropy for Efficient and Stable Blue-Emitting OLEDs.

In this study, we report a spatial planarization strategy for asymmetric Ir(III) complexes that simultaneously improves exciton stability and optical outcoupling in blue OLEDs. By incorporating bulky tert-butylcarbazole (tBuCz) units into tridentate N-heterocyclic carbene ligands, the molecular geometry is sterically confined into a more coplanar and anisotropic configuration. This structural planarization increases exciton binding energy and shortens the radiative lifetime, thereby stabilizing bound excitons against thermally activated dissociation while accelerating radiative exciton consumption. At the same time, the enhanced geometric anisotropy induces a highly horizontal emitting dipole orientation (EDO) of approximately 95%, enabling efficient intrinsic light extraction. Beyond its role as an emitter, the planarized Ir(III) complex further has a cooperative alignment effect in hyper-OLED architectures. This structural and electrostatic templating effect transfers molecular alignment to the terminal multiple-resonance TADF emitter v-DABNA, leading to secondary dipole ordering with an EDO of 98%. As a result, the optimized blue hyper-OLED achieves ultra-narrow emission at 470 nm with a full width at half maximum of 22 nm, a maximum external quantum efficiency of 36.9%, and an operational lifetime (LT50, time to 50% initial luminance) of 446 h at 1000 cd m-2. These results establish spatial planarization as a powerful molecular design principle for coupling exciton stabilization, dipole orientation control, and interfacial alignment transfer, providing a general strategy for efficient and stable blue OLEDs.