Anomalous circularly polarized light emission in organic light-emitting diodes caused by orbital–momentum locking
Li Wan, Yizhou Liu, Matthew J. Fuchter, Binghai Yan
Abstract
Chiral circularly polarized (CP) light is central to many photonic technologies, from the 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 enable the emission of strongly dissymmetric CP light from organic light-emitting diodes (OLEDs). It has been widely accepted that the molecular chirality of the active layer determines the favoured light handedness of the CP emission in such devices, 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 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. Circularly polarized light emitted from OLEDs exhibits opposite handedness depending on the propagation direction of the light. Switching the current flow in the OLED also switches the light handedness.