Stable Spiro‐Linked Terfluorenes with Triphenylamine Pendants as Deep Blue Emitters for Solution‐Processed Organic Light‐Emitting Diodes

Abstract

Herein, we reported new spiro‐linked terfluorenes (TF1 and TF2) as solution‐processible hole‐transporting‐free deep‐blue fluorescent emitters for simple structured organic light‐emitting diodes (OLEDs). They were designed and synthesized by incorporating triphenylamine pendants into the C9 positions of the spiro‐linked terfluorene, resulting in a criss‐cross configuration of the two terfluorene backbones and a highly bulky molecular geometry from the pendant groups. Consequently, TF1 and TF2 exhibited good quality thin films by spin‐coating, stable deep blue emissions with no unwanted long wavelength emission after prolonged thermal annealing and UV exposure, shallow highest occupied molecular orbital energy levels (−5.36–−5.37 eV), decent hole mobilities (1.09–1.23×10−7 cm2 V−1 s−1), and high thermal stability, and effectively employed as non‐doped emissive layers in the OLEDs. Particularly, TF2‐based solution‐processed OLED displayed a bright deep blue emission with superior EL performance (turn‐on voltage (Von) of 3.4 V, external quantum efficiency (EQEmax) of 3.82 %, and luminance efficiency (LEmax) of 5.22 cd A−1). This outstanding EL performance of the non‐doped solution‐processed deep blue OLED could be attributed to the effective molecular design, and this work presented a new approach for constructing effective blue emitters based on oligofluorenes.

Advances in Host-Free White Organic Light-Emitting Diodes Utilizing Thermally Activated Delayed Fluorescence: A Comprehensive Review

“…The EQE of the device reaches 3.3% at a brightness of 1000 lm/W, which has a rather low efficiency roll-off. It is one of the most efficient host-free blue OLED devices using traditional AIE fluorescent layers without any external coupling method [ 65 , 66 , 67 ].…”