Researchers make OLEDs brighter by tuning their chirality
Presenting their findings in a paper titled ‘Inverting the Handedness of Circularly Polarized Luminescence from Light-Emitting Polymers Using Film Thickness’ published in ACS Nano, the researchers report that blending achiral polymers with chiral small-molecule additives in the new polymer OLEDs chemistry allowed them to control the handedness/sign of the circularly polarized light through absolute stereochemistry. Another interesting finding is that tuning the circularly polarized light output was performed as a function of the active layer thickness, for a fixed optical isomer of the chiral additive.
through varying the OLED active layer thickness.
The paper reports bright circularly polarized polymer OLEDs (CP-PLEDs) capable of delivering 8000 cd/m2 with an efficiency of 4.0 cd/A and a high dissymmetry of emission of both left-handed (LH) and right-handed (RH) light, depending on the emitter’s thickness. In their experiments and using the same additive, varying the film thickness from 110nm to 160nm was enough to switch the handedness of the polarized light.
based polymers for light emitting diodes.
The implications for OLED displays is important, as typically, over half of the light they emit is blocked by the polarized anti-glare filter fitted onto the screens of smartphones and TVs. Engineering OLEDs with a precisely controlled circularly polarized light output to match the polarization of the anti-glare filter would yield an overall much brighter display or one that would have double the energy efficiency for the same brightness while maintaining a good readability even on a bright sunny day.
While their study was focused on OLEDs for displays, the team anticipates that the new chemistry and the polarised light generated by their materials could also find applications in the storage, transmission and encryption of information through the design of new photonic devices.
Imperial College – www.imperial.ac.uk
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