Matrix‐Free Hyperfluorescent Organic Light‐Emitting Diodes Based on Carbene–Metal–Amides
Hwan‐Hee Cho, Alexander S. Romanov, Manfred Bochmann, Neil C. Greenham, Dan Credgington
Abstract
Abstract A wide‐gap host matrix is a major obstacle detrimentally influencing the performance of hyperfluorescent organic light‐emitting diodes since it substantially increases driving voltage. Moreover, these hyperfluorescent devices typically require at least three components in their emitting layer, which is unfavorable for mass production. To tackle the issue, hyperfluorescent organic light‐emitting diodes are reported based on a two‐component emissive system of carbene–metal–amide donors and conventional fluorescent acceptors. A significant reduction of the driving voltage versus three‐component hyperfluorescent devices at practical brightness (1000 cd m –2 ) is demonstrated, leading to a doubling of power conversion efficiency for some composites. From an analysis of thin‐film photophysics, it is shown that operational efficiency is limited by Dexter energy transfer between donors and acceptors, which may be reduced by tert ‐butyl steric substituents, providing new targets for molecular design. While reducing driving voltage, matrix‐free hyperfluorescent devices also achieve a maximum external quantum efficiency of 16.5%.