Deep Blue Phosphorescent Organic Light-Emitting Diodes with CIEy Value of 0.11 and External Quantum Efficiency up to 22.5%

Abstract

Organic light-emitting diodes (OLEDs) based on red and green phosphorescent iridium complexes are successfully commercialized in displays and solid-state lighting. However, blue ones still remain a challenge on account of their relatively dissatisfactory Commission International de L'Eclairage (CIE) coordinates and low efficiency. After analyzing the reported blue iridium complexes in the literature, a new deep-blue-emitting iridium complex with improved photoluminescence quantum yield is designed and synthesized. By rational screening host materials showing high triplet energy level in neat film as well as the OLED architecture to balance electron and hole recombination, highly efficient deep-blue-emission OLEDs with a CIE at (0.15, 0.11) and maximum external quantum efficiency (EQE) up to 22.5% are demonstrated. Based on the transition dipole moment vector measurement with a variable-angle spectroscopic ellipsometry method, the ultrahigh EQE is assigned to a preferred horizontal dipole orientation of the iridium complex in doped film, which is beneficial for light extraction from the OLEDs.

A deep-blue-emissive iridium complex Ir(fdpt)₃ and its reference complex Ir(dpt)₃ are synthesized and studied. A series of phosphorescent organic light-emitting diodes (OLEDs) are fabricated with material screening. The optimal device shows excellent external quantum efficiency (EQE) up to 22.5% with a Commission International de L'Eclairage (CIE) coordinates of (0.15, 0.11), reaching the highest EQE among the OLEDs with comparable deep blue emissions.

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