Bright Side with Brannan | Circularly Polarised OLEDs: Why Are Researchers So Interested?

This is the second article in Bright Side with Brannan, a column by Prof. Alexander Brannan of the University of Manchester. In this column, Prof. Brannan explores the science behind OLED technology — the materials, the physics, and the open questions driving the field forward. You can read the first article in the series, on open-shell radical emitters, here.

In my previous article on radical OLED emitters, I briefly mentioned circularly polarised luminescence, or CPL, as an emerging direction for TTM-based materials.[1] Since then, the first CP-OLEDs based on donor–acceptor-type neutral TTM radicals have been reported, with g_EL reaching 7.2 × 10⁻³.[2] This shows that the area is continuing to grow, but what does that value actually mean for an OLED display? As CPL appears increasingly often in emitter research and OLED-Info coverage, I wanted to give a simple overview of why it is attracting interest, how researchers are trying to produce it, and where it may realistically be useful.

What is CPL?

Light consists of oscillating electric and magnetic fields, but polarisation is usually described using the electric field. In unpolarised light, this field has no fixed orientation. A linear polariser selects one direction, while a correctly aligned quarter-wave plate changes this back-and-forth motion into a rotating electric field. This produces circularly polarised light, often pictured as a left- or right-handed corkscrew. CPL can also be generated directly by a chiral emitting material or organised chiral system, without requiring these external optical components.[3]