Anomalous circularly polarized light emission in organic light-emitting diodes caused by orbital-momentum locking

TL;DR

This paper uncovers a novel direction-dependent circularly polarized light emission in OLEDs caused by orbital-momentum locking, which can be controlled by current flow and enhances polarization efficiency.

Contribution

It reveals that opposite propagation directions produce opposite CP handedness and that reversing current flow switches CP handedness, linking topological electronic properties to CP emission.

Findings

Opposite CP propagation directions have opposite handedness.

Reversing current flow switches CP handedness.

Direction-dependent CP emission significantly improves polarization rate.

Abstract

Chiral circularly polarized (CP) light is central to many photonic technologies, from optical communication of spin information to novel display and imaging technologies. As such, there has been significant effort in the development of chiral emissive materials that allow for the emission of strongly dissymmetric CP light from organic light-emitting diodes (OLEDs). A consensus for chiral emission in such devices is that the molecular chirality of the active layer determines the favored light handedness of CP emission, regardless of the light-emitting direction. Here, we discover that, unconventionally, oppositely propagating CP light exhibits opposite handedness, and reversing the current-flow in OLEDs also switches the handedness of the emitted CP light. This direction-dependent CP emission boosts the net polarization rate by orders of magnitude by resolving an established issue in CP-OLEDs, where the CP light reflected by the back electrode typically erodes the measured dissymmetry. Through detailed theoretical analysis, we assign this anomalous CP emission to a ubiquitous topological electronic property in chiral materials, namely the orbital-momentum locking. Our work paves the way to design new chiroptoelectronic devices and probes the close connections between chiral materials, topological electrons, and CP light in the quantum regime.