Highly efficient nondoped blue electroluminescence based on hybridized local and charge-transfer emitter bearing pyrene-imidazole and pyrene

Organic light-emitting diodes (OLEDs) have been explored and utilized in many fields of flat-panel displays nowadays because of their plentiful advantages such as lightweight, high flexibility, high picture quality, etc., and are hopeful to be the next-generation displays. However, improvements to the efficiency of blue OLEDs are still vital to OLEDs as replacements for liquid crystal display technology. A blue light-emitting material is one of the key components in the preparation of OLED displays. Designing molecule based on donor-acceptor (D-A) structure with a hybridized local and charge transfer (HLCT) excited state is a appealing strategy for providing an efficient OLED with high external quantum efficiency through efficacious exciton utilization. Herein, a highly efficient blue emitter, PyI-Py, is constructed combining pyrene[4,5-d]imidazole (weak donor) and pyrene (weak acceptor). The non-doped blue OLED exhibits excellent performance with a maximum current efficiency of 15.74 cd A(-1), a maximum external quantum efficiency (eta(ext)) of 9.13% and a maximum brightness of as high as 91097 cd m(-2) which is rarely obtained for a non-doped blue OLED. Moreover, the eta(ext) can reach 9.05% at very high brightness of 10000 cd m(-2), displaying extremely low efficiency roll-off of 0.9% which displays great superiorities in contrast with most thermally activated delayed fluorescent materials. The device characteristics lie among the highest values in non-doped blue OLEDs based on HLCT emitter and correspond to the best performance achieved for non-doped pyrene-based blue OLEDs to date. A maximum exciton utilization efficiency of 65% is harvested. The superior performance is attributed to the proper donor-acceptor design strategy which results in a HLCT excited state with the generation of a high proportion of singlet excitons.

Automated summary

Organic light-emitting diodes (OLEDs) have been widely explored and utilized in flat-panel displays recently for their advantages such as lightweight, high flexibility, and high picture quality, with the potential to become the next-generation display technology. Improving the efficiency of OLEDs, particularly blue OLEDs, is crucial for their application as replacements for liquid crystal display technology. By designing molecules based on a donor-acceptor structure with a hybridized local and charge transfer excited state, efficient OLEDs with high external quantum efficiency can be achieved through effective exciton utilization.