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

Abstract 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 luminance L_EL = 100 cd m⁻², and CE = 75.00 cd A⁻¹ at L_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.