Multi-Pulse Terahertz Spectroscopy Unveils Hot Polaron Photoconductivity Dynamics in Metal-Halide Perovskites

TL;DR

This study uses advanced terahertz spectroscopy to explore hot carrier dynamics and polaron effects in metal-halide perovskites, revealing localized lattice heating impacts on carrier mobility relevant for solar cell efficiency.

Contribution

Introduces a novel PPP-THz spectroscopy method to monitor real-time hot carrier conductivity and uncovers the role of polaron-lattice interactions in MHPs.

Findings

Mobility decreases with energy deposition, typical of band-transport.

Conductivity recovery is independent of hot carrier density.

Localized lattice heating significantly affects hot carrier mobility.

Abstract

The behavior of hot carriers in metal-halide perovskites (MHPs) present a valuable foundation for understanding the details of carrier-phonon coupling in the materials as well as the prospective development of highly efficient hot carrier and carrier multiplication solar cells. Whilst the carrier population dynamics during cooling have been intensely studied, the evolution of the hot carrier properties, namely the hot carrier mobility, remain largely unexplored. To address this, we introduce a novel ultrafast visible pump - infrared push - terahertz probe spectroscopy (PPP-THz) to monitor the real-time conductivity dynamics of cooling carriers in methylammonium lead iodide. We find a decrease in mobility upon optically depositing energy into the carriers, which is typical of band-transport. Surprisingly, the conductivity recovery dynamics are incommensurate with the intraband relaxation measured by an analogous experiment with an infrared probe (PPP- IR), and exhibit a negligible dependence on the density of hot carriers. These results and the kinetic modelling reveal the importance of highly-localized lattice heating on the mobility of the hot electronic states. This collective polaron-lattice phenomenon may contribute to the unusual photophysics observed in MHPs and should be accounted for in devices that utilize hot carriers.