Intrinsically Stretchable Phosphorescent Light-Emitting Materials for Stretchable Displays.

Intrinsically stretchable organic light-emitting diodes ( is- 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 ( isp- 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) 3 ). The poly(ethylene glycol)- block -poly(propylene glycol)- block -poly(ethylene glycol) (PEG-PPG-PEG) additive significantly improved the stretchability (∼100% strain), brightness (∼5400 cd/m 2 ), and efficiency (∼25.3 cd/A) of the isp- EML compared with a conventional phosphorescent EML (approximately 3% strain, 3750 cd/m 2 , and 12.1 cd/A). Furthermore, by changing the emitting dopant in the isp- EML, we could control the red, green, and blue emission colors, with increasing mechanical and electrical properties of the isp- 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.