PtAu3 cluster complexes with narrow-band emissions for solution-processed organic light emitting diodes

Abstract

In order to develop solution-processable organic light-emitting diodes (OLEDs) with improved optical properties, PtAu₃ heterometallic cluster complexes that exhibit narrow-band emission spectra were prepared through judicious molecular design. The brightly emissive PtAu₃ complexes with robust chemical and thermal stability (>290 °C) show photoluminescence quantum yields (PLQY) of 80.5% to 90.1% in doped films. The dihedral angle between the plane of the aromatic acetylide and the platinum(II) coordination square plane exerts dramatic influence on the full width at half maximum (FWHM) of phosphorescent emission, in which the better the co-planarity, the narrower the FWHM. Theoretical studies suggest that the greater involvement of the acetylide-to-Pt ³LMCT state favors narrow-band emission. Solution-processed OLEDs based on narrow-band green emitters afford a maximum current efficiency (CE) of 38.7 cd A⁻¹, power efficiency (PE) of 22.9 lm W⁻¹ and external quantum efficiency (EQE) of 10.3% with an FWHM of 42 nm and CIE coordinates of (0.30, 0.61). The PtAu₃ cluster complex with phenanthrene-fused carbazole-acetylide displays improved device performance due to its enhanced hole-carrier ability, with a peak CE of 62.2 cd A⁻¹, PE of 30.3 lm W⁻¹ and EQE of 16.6%. The elegant synthetic strategy combining electron and/or hole transport units enhances not only the device performance of the PtAu₃ cluster complexes but also their charge carrier abilities, which were analyzed through space charge limited current measurements.