Intrinsically Stretchable Phosphorescent Light-Emitting Materials for Stretchable Displays.

Intrinsically stretchable organic light-emitting diodes (OLEDs) have attracted significant attention for use in next-generation displays. However, most studies conducted to date have focused on how to make fluorescent materials stretchable, utilizing singlet excitons with a theoretical internal quantum efficiency (IQE) of 25%. Although phosphorescent materials have a high theoretical IQE of 100%, no previous work has attempted to develop stretchable phosphorescent light-emitting materials. In this work, we designed a solution-processable and intrinsically stretchable phosphorescent light-emitting layer (EML) by blending various additives together with a mixture of a polymer host, poly(9-vinyl carbazole) (PVK), and a small-molecule emitting dopant, tris(2-phenylpyridine)iridium(III) (Ir(ppy)). The poly(ethylene glycol)--poly(propylene glycol)--poly(ethylene glycol) (PEG-PPG-PEG) additive significantly improved the stretchability (∼100% strain), brightness (∼5400 cd/m), and efficiency (∼25.3 cd/A) of the EML compared with a conventional phosphorescent EML (approximately 3% strain, 3750 cd/m, and 12.1 cd/A). Furthermore, by changing the emitting dopant in the EML, we could control the red, green, and blue emission colors, with increasing mechanical and electrical properties of the EML. These results highlight the promising potential of the novel blend system using phosphorescent materials and additives for application in highly stretchable and efficient OLEDs.