Remarkable enhancement of efficiencies for red, green, and blue tandem phosphorescent organic light-emitting diodes by utilizing a non-doped photovoltaic-type charge generation unit

Abstract

We have achieved a remarkable enhancement in current efficiencies and power efficiencies for red, green, and blue tandem phosphorescent organic LEDs (T-PhOLEDs) by employing LiF/Al/fullerene/zinc-phthalocyanine/MoO 3 as a charge generation unit (CGU). Fullerene/zincphthalocyanine with a proper absorption property in the visible region can absorb a part of photons from emission layers within T-PhOLEDs, which facilitates the charge generation and separation within CGU. At the identical luminance of 1,000 cd m −2 , the current efficiencies for red, green, and blue T-PhOLEDs are 3.3-, 2.1-, and 2.9-fold those of the corresponding single-unit devices, and power efficiencies are increased by 72.2%, 13.6%, and 37.2%, respectively. © 2019 The Japan Society of Applied Physics C 60 (5 nm)/ZnPc(5 nm) exhibits the highest transmittance level over the entire visible range. Additionally, the efficient charge generation and separation within the CGU are vital for T-PhOLEDs. For studying the charge generation and separation processes of the CGU, a

Highly efficient tandem blue phosphorescent organic LEDs with external quantum efficiency exceeding 42%

“…[9][10][11][12] We have demonstrated that the multilayer structure CGU of LiF/Al/C 60 /ZnPc/MoO 3 possesses excellent charge generation, separation and injection capabilities when the ETL of TPBi and the HTL of NPB were used. 22) Since the LUMOs of TPBi and TmPyPB are −2.7 eV and the HOMO difference between NPB and TAPC is only 0.1 eV, the CGU also possesses excellent charge generation abilities when the ETL and HTL are TmPyPB and TAPC, respectively. To clarify this point, the external carrier-excluding device E: ITO/TmPyPB(40 nm)/LiF(0.5 nm)/Al(1 nm)/C 60 (5 nm)/ZnPc (5 nm)/MoO 3 (3 nm)/TAPC(60 nm)/Al was fabricated.…”