High-efficiency red and green light-emitting polymers based on a novel wide bandgap poly(2,7-silafluorene)

A new type of high-efficiency red and green light-emitting polymer was synthesized via the Suzuki coupling reaction by incorporating narrow bandgap (NBG) comonomers 4,7-di(4-hexyl-2-thienyl)-2,1,3-benzothiadiazole (DHTBT) and 2,1,3-benzothiadiazole (BT), respectively, into the backbone of poly(2,7-silafluorene) (PSiF). The thermal, photophysical, electrochemical and electroluminescent properties of the PSiF copolymers were investigated and compared with those of the corresponding polyfluorene (PF)-based polymers. The advantages of polymers with PSiF as the main chain over PFs were confirmed by comparison of the electroluminescent performances of PSiF-DHTBT10 and PSiF-BT10 with those of the PF-based copolymers with the same NBG content. Preliminary results showed that the device efficiencies of the emitters containing the same NBG units in the PSiF main chain are higher than those based on PFs. The devices with the configuration of ITO/PEDOT : PSS/PVK/polymer/Ba/Al showed the maximum external quantum efficiency (EQE) of 2.89% and current efficiency (CE) of 2.0 cd A−1 with CIE coordinates of (0.67, 0.33) for PSiF-DHTBT10 and the maximum EQE of 3.81% and CE of 10.6 cd A−1 with CIE coordinates of (0.38, 0.57) for PSiF-BT10, respectively, which are among the best results of fluorescent red or green light-emitting polymers reported so far, indicating PSiF derivatives are a promising class of light-emitting polymers.