title: Balance the Carrier Mobility To Achieve High Performance Exciplex OLED Using a Triazine-Based Acceptor.
abstract: A star-shaped 1,3,5-triazine/cyano hybrid molecule CN-T2T was designed and synthesized as a new electron acceptor for efficient exciplex-based OLED emitter by mixing with a suitable electron donor (Tris-PCz). The CN-T2T/Tris-PCz exciplex emission shows a high ΦPL of 0.53 and a small ΔET-S = -0.59 kcal/mol, affording intrinsically efficient fluorescence and highly efficient exciton up-conversion. The large energy level offsets between Tris-PCz and CN-T2T and the balanced hole and electron mobility of Tris-PCz and CN-T2T, respectively, ensuring sufficient carrier density accumulated in the interface for efficient generation of exciplex excitons. Employing a facile device structure composed as ITO/4% ReO3:Tris-PCz (60 nm)/Tris-PCz (15 nm)/Tris-PCz:CN-T2T(1:1) (25 nm)/CN-T2T (50 nm)/Liq (0.5 nm)/Al (100 nm), in which the electron-hole capture is efficient without additional carrier injection barrier from donor (or acceptor) molecule and carriers mobilities are balanced in the emitting layer, leads to a highly efficient green exciplex OLED with external quantum efficiency (EQE) of 11.9%. The obtained EQE is 18% higher than that of a comparison device using an exciplex exhibiting a comparable ΦPL (0.50), in which TCTA shows similar energy levels but higher hole mobility as compared with Tris-PCz. Our results clearly indicate the significance of mobility balance in governing the efficiency of exciplex-based OLED. Exploiting the Tris-PCz:CN-T2T exciplex as the host, we further demonstrated highly efficient yellow and red fluorescent OLEDs by doping 1 wt % Rubrene and DCJTB as emitter, achieving high EQE of 6.9 and 9.7%, respectively.
authors.affiliation: Institute of Optoelectronic Sciences, National Taiwan Ocean University , Keelung 202, Taiwan.
authors.forename: Wen-Yi
authors.initials: WY
authors.lastname: Hung
authors.affiliation: Institute of Optoelectronic Sciences, National Taiwan Ocean University , Keelung 202, Taiwan.
authors.forename: Pin-Yi
authors.initials: PY
authors.lastname: Chiang
authors.affiliation: Department of Chemistry, National Taiwan University , Taipei 106, Taiwan.
authors.forename: Shih-Wei
authors.initials: SW
authors.lastname: Lin
authors.affiliation: Department of Chemistry, National Taiwan University , Taipei 106, Taiwan.
authors.forename: Wei-Chieh
authors.initials: WC
authors.lastname: Tang
authors.affiliation: Department of Chemistry, National Taiwan University , Taipei 106, Taiwan.
authors.forename: Yi-Ting
authors.initials: YT
authors.lastname: Chen
authors.affiliation: Department of Chemistry, National Taiwan University , Taipei 106, Taiwan.
authors.forename: Shih-Hung
authors.initials: SH
authors.lastname: Liu
authors.affiliation: Department of Chemistry, National Taiwan University , Taipei 106, Taiwan.
authors.forename: Pi-Tai
authors.initials: PT
authors.lastname: Chou
authors.affiliation: Department of Chemistry, National Taiwan University , Taipei 106, Taiwan.
authors.forename: Yi-Tzu
authors.initials: YT
authors.lastname: Hung
authors.affiliation: Department of Chemistry, National Taiwan University , Taipei 106, Taiwan.|Institute of Atomic and Molecular Science , Taipei 106, Taiwan.
authors.forename: Ken-Tsung
authors.initials: KT
authors.lastname: Wong
keywords: 1,3,5-triazine; balance mobility; electron-transporting material; exciplex; thermally activated delayed fluorescence (TADF)