Efficient green-light-emitting diodes from silole-containing copolymers

Two random copolymers based on poly(di-n-hexylfluorene-co-4,4-diphenyldithienosilole) (PF-DTS) were synthesized by Suzuki coupling reaction. The presence of a small portion (10 mol% for PF9-DTS, 5 mol% for PF19-DTS) of electron-deficient dithienosilole moiety in the copolymers increases their electron affinity and facilitates charge recombination through its function as a charge-trapping site for both holes and electrons. Photoluminescence (PL) studies show that color tuning through efficient Förster energy transfer from the higher-energy fluorene segments to the lower-energy dithienosilole-containing segments can be achieved as well. A double-layer device using PF9-DTS as the emitting layer and an in-situ polymerized bis-tetraphenylenebiphenyldiamine-perfluorocyclobutane (BTPD-PFCB) as the hole-transporting layer demonstrates a low turn-on voltage at 4.6 V, a brightness greater than 25 900 cd/m², and a maximum external quantum efficiency of 1.64%, which could be attributed to both the improved charge injection and charge recombination in this polymer.