Thermally Activated Delayed Fluorescent Dendrimers that Underpin High‐Efficiency Host‐Free Solution‐Processed Organic Light‐Emitting Diodes
Dianming Sun, Eimantas Du̅da, Xiao‐Chun Fan, Rishabh Saxena, Ming Zhang, Sergey Bagnich, Xiaohong Zhang, Anna Köhler, Eli Zysman‐Colman
Abstract
Abstract The development of high‐performance solution‐processed organic light‐emitting diodes (OLEDs) remains a challenge. An effective solution, highlighted in this work, is to use highly efficient thermally activated delayed fluorescence (TADF) dendrimers as emitters. Here, the design, synthesis, density functional theory (DFT) modeling, and photophysics of three triazine‐based dendrimers, tBuCz2pTRZ , tBuCz2mTRZ , and tBuCz2m2pTRZ , is reported, which resolve the conflicting requirements of achieving simultaneously a small Δ E ST and a large oscillator strength by incorporating both meta ‐ and para ‐connected donor dendrons about a central triazine acceptor. The solution‐processed OLED containing a host‐free emitting layer exhibits an excellent maximum external quantum efficiency (EQE max ) of 28.7%, a current efficiency of 98.8 cd A −1 , and a power efficiency of 91.3 lm W −1 . The device emits with an electroluminescence maximum, λ EL , of 540 nm and Commission International de l'Éclairage (CIE) color coordinates of (0.37, 0.57). This represents the most efficient host‐free solution‐processed OLED reported to date. Further optimization directed at improving the charge balance within the device results in an emissive layer containing 30 wt% OXD‐7, which leads to an OLED with the similar EQE max of 28.4% but showing a significantly improved efficiency rolloff where the EQE remains high at 22.7% at a luminance of 500 cd m −2 .