Ultrafast spin-resolved spectroscopy reveals dominant exciton dynamics in conducting polymer polyaniline

TL;DR

This study uses ultrafast spin-resolved spectroscopy to demonstrate that excitons predominantly govern the charge relaxation dynamics in conducting polymer polyaniline, clarifying debates on its photo-generated charge nature.

Contribution

The paper provides experimental evidence that excitons, not polarons, dominate the non-equilibrium optical response of PANI, using spin-resolved spectroscopy to reveal spin-polarized charge dynamics.

Findings

Charge relaxation in PANI is exciton-dominated.

Charge dynamics exhibit strong spin polarization.

No spin-flip process involved in charge relaxation.

Abstract

The conducting polymer polyaniline (PANI) has a wide range of optoelectronic applications due to its unique electronic and optical characteristics. Although extensive works have been performed to understand the equilibrium properties, the nature of the charge type that governs its non-equilibrium optical response has been barely understood; a number of studies have debated the nature of photo-generated charge type in PANI, specifically whether it is polaron or exciton based. Here, we report experimental evidence that the charge relaxation dynamics of PANI are dominated by excitons. Utilizing ultrafast spin-resolved pump-probe spectroscopy, we observed that PANI charge dynamics are strongly spin-polarized, exhibiting a spin Pauli-blocking effect. Investigations including both spin-independent and spindependent dynamics reveal that there is no spin-flip process involved in charge relaxation. This provides compelling evidence of an exciton-dominated photo-response in PANI.