A cross-linkable, organic down-converting material for white light emission from hybrid LEDs

The use of organic materials and the replacement of rare-earth elements in the making of light-emitting devices has been increasingly popular over the last decades. Herein, the synthesis and characterisation of a novel organic green-emitting material (GreenCin), based on a fluorene-benzothiadiazole-fluorene (Flu-BT-Flu) core structure, and its performance as a down-converting layer in tandem with commercial blue light-emitting diodes (LEDs) for white light emission are reported. This material has been functionalised with cinnamate-groups to enable the emissive material to react with the cross-linker tetra(cinnamoyloxymethyl)methane (TCM), to produce stable films with high performance in hybrid LEDs. The hybrid devices can generate white light with a good colour rendering index (CRI) of 69. The hybrid devices also have x2.6 increased luminous efficacy (107 lm W-1) and x2.4 increased radiant flux (24 mW) when compared with hybrid devices using non-cross-linked analogues of GreenCin. Additionally, the hybrid devices containing GreenCin have a high blue-to-white efficacy value (defined by dividing the luminous flux of a hybrid device by the radiant flux of the underlying blue LED), of 213 lm W-1, for which inorganic phosphors have values in the range of 200-300 lm W-1.

Automated summary

The use of organic materials and the replacement of rare-earth elements in light-emitting devices have become popular recently. This study presents the synthesis and characterisation of a novel organic green-emitting material (GreenCin) and its performance as a down-converting layer in hybrid LEDs. The hybrid devices offer improved luminous efficacy, radiant flux, and blue-to-white efficacy compared to devices without cross-linked analogues of GreenCin.