Interplay of Hot Carrier Relaxation and Trapping in Red Emissive Formamidinium Lead Iodide Perovskite Nanorods

Abstract

Stable, red-emissive formamidinium lead triiodide (FAPbI 3 ) nanorods have been synthesized by modification of conditions for the synthesis of FAPbI 3 nanocubes. The bimodal PL decays with components of 9 ns and 30 ns are ascribed to trap-assisted radiative recombination. Transient absorption spectroscopy at different pump wavelengths and fluences indicates the involvement of phonon bottleneck effect in hot carrier relaxation. Global analysis of transient absorption data yields four components. The two fastest ones (0.5-3.7 ps) are ascribed to two different hot carrier cooling pathways. The tens of picosecond component is attributed to ground state bleach associated with band-edge transition. The longest component (>1 ns, negative signal corresponding to stimulated emission, Stokes shifted with respect to the band gap) is attributed to radiative recombination involving mid-gap trap states. Hence, a detailed understanding of the interplay of hot carrier cooling and trapping in the exciton dynamics, leading to the population of radiative trap states, is obtained.