Molecular-Scale Strategies to Achieve High Efficiency and Low Efficiency Roll-off in Simplified Solution-Processed Organic Light-Emitting Diodes

Solution-processed small-molecule organic light-emitting diodes (OLEDs) are regarded as next-generation flat-panel displays and solid-state lighting sources due to low material loss and a simple device fabrication process. However, they still suffer from low device efficiency and severe efficiency roll-off. Here, molecular-scale strategies are proposed to achieve highly efficient solution-processed small-molecule OLEDs with reduced efficiency roll-off. By combining experiments with ab initio and molecular dynamics simulations, it is shown that an acetylacetonate group in a phosphorescent dopants lowers the dipole moment and molecular interaction energy of dopants, reducing dopant aggregation and increasing charge carrier transport. Furthermore, a charge-balance assistant molecule is incorporated in the mixed-host emitting layer to increase the balance of charge carrier transport and to broaden the exciton recombination zone in the center of the emitting layer. The resulting OLEDs have a current efficiency (CE) of 103.7 cd A(-1), which is the highest yet reported in solution-processed OLEDs, and low efficiency roll-off (CE=99.68 cd A(-1)at a luminanceL(EL)=100 cd m(-2), and CE=75.00 cd A(-1)atL(EL)=1000 cd m(-2)) even with the simplified device architecture. It is expected that this strategy will advance the feasibility of commercialization of low-cost high-efficiency OLEDs.