A phosphorated spirobi[thioxanthene] host matrix enables high-efficiency simple white thermally activated delayed fluorescence diodes

• All-TADF WOLEDs with the state-of-the-art power efficiency > 70 lm W −1 . • A new spiro host based on 9,9′-spirobi[thioxanthene] core and phosphine oxide group. • Optimized intermolecular interactions for optoelectronic property enhancement. • Synergistic effect of energy transfer and TADF transition in radiation. Host matrix is crucial for optimizing exciton allocation in all Thermally activated delayed fluorescence (TADF) white Organic light-emitting diodes (OLED). However, only few spiro hosts are competent since unbalanced steric and electronic effects. Herein, a new spiro core 9,9′-spirobi[thioxanthene] (ST) based host STDPO is reported, whose two peripheral diphenylphosphine oxide (DPPO) groups are incorporated to construct tridimensional steric hindrance and Intermolecular hydrogen bond (IHB) network. As consequence, STDPO achieves the high enough first triplet (T 1 ) energy level of 2.93 eV and favorable electron mobility ( µ e ) by the level of 10 −5 cm 2 V −1 s −1 . Simultaneously, the well-modulated intermolecular interactions in STDPO matrix give rise to the synergistic effect of blue and yellow TADF dopants in exciton utilization. The increased rate constants and efficiencies of radiative transitions and reduced nonradiative rate constants render a photoluminescence quantum yield as high as 90% and 100% exciton utilization efficiency of dually doped white TADF film. STDPO further endowed its single-emissive-layer TADF WOLEDs with the record η PE of 71.8 lm W −1 achieved by spiro hosts.