Highly efficient white-emitting thermally activated delayed fluorescence polymers: Synthesis, non-doped white OLEDs and electroluminescent mechanism

Highlights: • A series of white-emitting polymers with obvious TADF feature are successfully synthesized. • These polymers exhibit dual-color white emission with deep-blue and yellow emission. • EQE_max of the nodoped single polymer OLEDs reaches to 14.2% with CIE of (0.33, 0.42). • Langevin recombination is one of the main recombination pathways in these OLEDs. • Trap-assisted recombination can be take into account for partial electroluminescent mechanism. -- Abstract: Single white-emitting polymers are greatly desired to develop solution-processed white organic light-emitting diodes (WOLEDs) with simple fabrication processes and low-energy-consumption. Thermally activated delayed fluorescence (TADF) polymers harvesting both triplet and singlet excitons without heavy metals are promising candidates for solution-processable white-emitting devices. However, all-TADF polymers with efficient white emissions have not been well-developed. Herein, a new strategy is proposed to develop a series of all-TADF single white-emitting polymers for highly efficient non-doped solution-processed WOLEDs. A WOLED based on one of these polymers as the emitting layer achieves an EQE_max of 14.2%, a CE_max of 38.8 cd A⁻¹, and a PE_max of 20.3 lm W⁻¹ with the CIE coordinates of (0.33, 0.42) and (0.31, 0.39) at 100 cd m⁻² and 2000 cd m⁻², respectively. The double-channel trap-assisted and Langevin recombinations account for broad recombination zones, reduced formation of high-energy excitons on hosts and enhanced efficiency of PDTPT-1, 2&3 based OLEDs. As far as it is known, PDTPT-1 is the highest efficient white-emitting TADF polymer so far.