Anisotropy-guided interface molecular engineering for stable blue electroluminescence

Despite the emergence of interlayers with high triplet energies (T₁) to stabilize blue phosphorescent organic light-emitting diodes (PhOLEDs), a limited understanding of their molecular structures poses a challenge in preventing triplet exciton leakage while maintaining charge balance. Here, we report a rational design strategy for interlayers aimed at concurrently controlling T₁ and molecular arrangements conducive to charge transport. Four interlayer materials having high T₁ (∼3.0 eV) are developed as electron-blocking materials (EBMs), utilizing asymmetric orthogonal geometries with varying torsion angles and dipole moments. X-ray crystallographic analyses reveal that the EBM, featuring the most asymmetric charge distributions, exhibits a herringbone packing and a face-on orientation through dipole-induced anisotropic interactions, thereby promoting hole transport. The power efficiency and operational lifetime of the corresponding blue PhOLEDs increase by 24% and 21%, respectively, compared with a conventional EBM. This study offers extensive insights into designing interlayers with versatile applicability in optoelectronics harnessing triplets.