Direct evidence of dopant-dopant synergism in efficient single-emissive-layer white thermally activated delayed fluorescence

Highlights: • Direct evidences of synergism between blue and yellow emitters in TADF WOLEDs. • State-of-the-art efficiencies achieved by a combination of "weak" blue and "strong" yellow TADF emitters. • Exciton kinetics analysis based on transient photoluminescence and electroluminescence spectroscopies. • Compared to blue diodes, blue-yellow complementarity dramatically improved EQE of WOLEDs by 13 folds. Major efforts were previously devoted to incorporate high-efficiency blue dopants into thermally activated delayed fluorescence (TADF) white organic light-emitting diodes (WOLED). Herein, we demonstrate that the synergism of blue and yellow TADF dopants in terms of efficient exciton allocation and quenching suppression are more crucial for achieving high-performance single-emissive-layer TADF WOLEDs. Based on three blue TADF emitters xDMACPO with markedly stronger host characteristics but relatively lower photoluminescence (PL) quantum yields than a conventional blue TADF emitter DMAC-DPS, transient PL and electroluminescence (EL) analyses give the direct evidences that in contrast to serious emission quenching of DMAC-DPS by co-doping a yellow emitter 4CzTPNBu, 4CzTPNBu hardly reduces TADF performance of xDMACPO, but even improved EL efficiencies of xDMACPO through complementing with each other in exciton harvesting. xDMACPO in turn mitigate emission quenching of 4CzTPNBu, among which TDMACPO most compatible with 4CzTPNBu dramatically elevates the efficiencies of the TADF WOLED by one third.