Understanding and Manipulating the Interplay of Wide Energy Gap Host and TADF Sensitizer in High Performance Fluorescence OLEDs.
Comprising an emitting layer (EML) constituting a wide energy gap host, a thermally activated delayed fluorescence (TADF) sensitizer and a conventional fluorescent dopant, TADF sensitizing fluorescence organic light emitting diodes (TSF OLEDs) highly depend on component interplay to maximize their performance, which, however, is still under researched. Taking the host type (TADF or non TADF) and the recombination position (on the host or on the TADF sensitizer) into consideration, the interplay of host and TADF sensitizer is comprehensively studied and manipulated. A wide energy gap host with TADF and recombination of charges on it are both required to maximize device performances by triggering multiple sensitizing processes to eliminate exciton losses. Based on those findings, a maximum external quantum efficiency (EQE)/power efficiency (PE) of 23.2%/76.9 lm W 1 is realized with a newly developed TADF host, significantly outperforming the reference devices. Further device optimization leads to unprecedently high EQE/PE of 24.2%/89.5 lm W 1 and a half lifetime of over 400 h at an initial luminance of 2000 cd m 2 with the peak PE being the highest value among the reported TSF OLEDs. This work reveals the importance of manipulating the component interplay in EMLs, opening a new avenue toward highly efficient TSF OLEDs.
Advanced materials