Abstract
Considerable progress in organic light-emitting diodes (OLEDs) has triggered intensive effort to develop efficient solid-state electroluminescent (EL) materials over the past two decades. Among the many classes of materials being investigated, transition metal complexes are highly attractive because phosphorescent OLEDs containing Ir (III), Pt (II) and Os (II) complexes exhibit very high external quantum efficiencies (ηext). This is because such complexes effectively harvest triplet excitons, so their efficiencies are four times higher than that of conventional fluorescent OLEDs. However, phosphorescent OLEDs containing transition metal-based compounds are rather expensive and unsustainable because they contain rare metals. While OLEDs containing Cu (I) complexes that exhibit high ηext comparable to those with transition metal complexes have been examined as an alternative, the relatively low reliability and high driving voltage of such OLED are fundamental problems. Therefore, a novel way to realize high EL efficiency is required. Although fluorescent OLEDs have been assumed to show limited efficiency because of the branching ratio of singlet and triplet excitons of 1:3, the most recent fluorescence-based OLEDs have overcome this limitation using triplet-triplet annihilation and thermally activated delayed fluorescence (TADF) [1-2]. In particular, we have developed promising blue and green TADF materials [3-4]. However, the design of efficient orange or red emitters is inherently difficult because the photoluminescence (PL) quantum efficiency tends to decrease as the emission wavelength increases according to the energy gap law.
© 2013 Optical Society of America
PDF ArticleMore Like This
Takeshi Komino, Yuta Sagara, Hiroyuki Tanaka, Yuji Oki, Nozomi Nakamura, Hiroshi Fujimoto, and Chihaya Adachi
CE_3_4 The European Conference on Lasers and Electro-Optics (CLEO/Europe) 2017
Jin Won Sun and Jang-Joo Kim
SSM4C.2 Solid-State Lighting (SOLED) 2016
Mark Bown, James Macdonald, Jenny O’Connell, Michelle Groarke, Sven Andresen, Tony Wilson, Alex Bilyk, Melissa Skidmore, Tadahiko Hirai, Andrew Scully, and Kazunori Ueno
DTh4C.2 Solid-State and Organic Lighting (SOLED) 2014