Thermally Activated Delayed Fluorescence Polymers with Welldefined Structure to Explore Structure-Performance Correlation

Abstract

Thermally activated delayed fluorescence (TADF) polymers are the ideal emission layers for solution-processed organic lightemitting diodes (OLEDs). However, most existing TADF polymers are characterized by random copolymer architectures, formed by means of multi-monomer copolymerization. The irregular distribution of TADF chromophore may lead to ambiguous structure-performance correlation and substantial challenge in achieving device stability. Herein, a series of structurally well-defined TADF polymers PyCzABP have been successfully synthesized by alternating copolymerization between TADF-based bromide monomers and oligomeric carbazole units, where y value represents the number of carbazole ring. Accordingly, TADF units are spatially separated by the oligomeric carbazole segment from P1CzABP to P5CzABP. As increasing y from 1 to 5, the photoluminescence quantum yields of the polymers gradually enhance from 62% to 89% with an almost identical emissive wavelength at 543 nm except for P1CzABP. Moreover, the non-doped and solution-processed OLED with P5CzABP achieves a maximum external quantum efficiency of 19.7% with a turn-on voltage of 2.5 V, which is superior to the random polymers with the similar TADF units.