Planar Pt(II) Complexes for Low-Doped Excimer-Based Phosphorescent Organic Light-Emitting Diodes

Two novel Pt(II) complexes of type Pt[N̂C–O–C′̂N′], Pt(pzpyOppz-A) and Pt(pzpyOppz-B), were developed for excimer-based emissions. N̂C and N′̂C′ are the motifs of substituted pyrazolyl-pyridyl (pzpy) and phenyl-pyrazolyl (ppz), respectively. The complexes can readily form dimers in a solid matrix, resulting in an excimer-based emission with high photoluminescence efficiency. By utilizing dual emission bands corresponding to the monomer and excimer, efficient phosphorescent organic light-emitting diodes (PhOLEDs) with a broad spectral emission were fabricated. The device employing Pt(pzpyOppz-A) achieves a broad yellowish-white emission with a full width at half-maximum of 152 nm at 3 wt % concentration and maximum external quantum efficiency (EQE), power efficiency (PE), and current efficiency (CE) of 20.7%, 43.9 Lm W–1, and 60.1 cd A–1, respectively, at a 5 wt % concentration. The device with 40 wt % Pt(pzpyOppz-B) therein exhibits an exclusive excimer-based emission with the maximum EQE, PE, and CE of 25.5%, 55.5 Lm W–1, and 62.3 cd A–1, respectively. This work shows the molecular art of the Pt(II) complex for highly performable phosphorescent devices via utilizing the in-situ-formed dimer in a simplified architecture.