Highly Efficient Thermally Activated Delayed Fluorescence Organic Light-Emitting Diodes with Fully Solution-Processed Organic Multilayered Architecture: Impact of Terminal-Substitution on Carbazole-Benzophenone Dendrimer and Interfacial Engineering.

A series of second generation carbazole-benzophenone dendrimer substituted by several functional groups at terminal positions (subG2B) was investigated toward thermally activated delayed fluorescence (TADF) emitter for non-doped emissive layer (EML) application in solution-processed organic light-emitting diode (OLED). Substitution was found to dramatically alter the photophysical properties of the dendritic TADF emitters. Introduction of tert-butyl and phenyl group endows the subG2Bs with aggregation-induced emission enhancement (AIEE) character by suppression of internal conversion in singlet excited states. In the meantime, introduction of methoxy group resulted in aggregation-caused quenching character. Device performance of the OLED, where subG2B neat films were incorporated as non-doped EMLs, was found to be highly enhanced by adopting fully solution-processed organic multilayer architecture in comparison to the devices with vacuum deposited electron transporting layer (ETL), achieving maximum external quantum efficiency of 17.0 %. Such improvement was attributable to the improved carrier balance via intermixing at solution-processed EML/ETL interfaces. It was also found that post thermal annealing of OLED at appropriate temperature could be beneficial to enhance OLED performance by promoting intermixing EML/ETL interface to some extent. Our findings emphasize the potential utility of dendritic TADF emitters in solution processed TADF-OLED and raise the importance to manipulate dendrimer/small molecule interfaces.