横山研究室の「安定蒸着可能なフッ素樹脂を用いた能動的屈折率制御による有機EL光取り出し効率の向上」に関する論文がJournal of Materials Chemistry C誌（IF 7.393）に掲載されました。また、「Journal of Materials Chemistry C Hot Papers」にも選定されました。本研究は、AGC株式会社および明治大学野口研究室との共同研究の成果です。
Active refractive index control using a stably evaporable perfluororesin for high-outcoupling-efficiency organic light-emitting diodes
Daisuke Yokoyama, Tatsuki Sasaki, Yasutaka Suzuki, Takefumi Abe, Kaori Tsuruoka, Tatsuya Miyajima, Toshifumi Kakiuchi, Chiho Morita, Masaharu Aoki, Yasuhiro Ouchi, Wataru Aita, Yasuhiro Kuwana, Yutaka Noguchi
The internal quantum efficiency of organic light-emitting diodes (OLEDs) has reached nearly 100%, and thus further improvement in the external quantum efficiency can be achieved only through outcoupling enhancement. However, light propagation in OLEDs for achieving high outcoupling has mainly been controlled not by the internal organic semiconductor layers but by external optical elements, which inevitably increase process cost. Here, a method is proposed for outcoupling enhancement that actively controls the refractive index of a hole transport layer (HTL) in OLEDs using a stably evaporable perfluororesin, which has a low refractive index and high amorphousness. The co-deposition of the perfluororesin with a hole transport material lowers the refractive index of the HTL to 1.56 at 550 nm without deteriorating the electrical properties. Owing to the nano-sized pillar-like phase separation between the perfluororesin and the hole transport material, the path of charge transport is
retained. Using the low-index co-deposited HTL, a 1.22-fold enhancement of the outcoupling efficiency of a phosphorescent OLED is demonstrated. The proposed method can be generally applied to OLEDs to significantly enhance their outcoupling efficiency without increasing process cost. The results show the potential of active refractive index control as a major strategy for achieving further high-efficiency OLEDs.