Sensitizer enabling long lifetime wet-processed candlelight OLEDs

Abstract

Blue hazard-free candlelight-style light sources are friendly to human eyes and physiology, ecosystems, night skies, and artifacts. Wet-process enables devices to be fabricated cost-effectively. However, wet-processed organic devices typically exhibit poor lifetime. We demonstrate here a fairly long lifetime wet-processed candlelight OLED with a simple structure. The lifetime was increased by 2.8 times by using 4,4′,4″-tris(carbazol-9-yl) triphenylamine as host in lieu of the typical 4,4′-bis(N-carbazolyl)-1,1′-biphenyl. Incorporation of a robust sensitizer further increased the lifetime by 93 times. The reasons why the lifetime was markedly enhanced may be mainly attributed to the facts that the sensitizer is thermally and electrochemically more stable, besides being more favorable to the injection of both electron and hole. The device showed a color temperature of 1770 K. From retinal protection perspective, this candlelight OLED permits at 100 lx an exposure-limit of 13 h, 150 times friendlier than that of the 5500 K cold-white LED (320 s) and 170 times friendlier than that of the 5920 K cold-white CFL (286 s). Upon a 1.5 h exposure at night, it would suppress melatonin secretion only by 2%, 9 times better than the LED (20%) and 14 times better than the CFL (29%).