Hot carrier harvesting at the interface of CsPbI3 nanocrystals

Abstract

We investigate the solution-phase harvesting of hot carriers (HCs) at the interface of CsPbI₃ nanocrystals (NCs) and N-methyl aniline (NMA). NMA, chosen for its specific band alignments, enables the extraction of above band-edge carriers thermodynamically favorable while effectively suppressing carrier transfer at the band-edge. Stern–Volmer (SV) analysis based on TCSPC-recorded lifetimes shows the carrier transfer rate approaches the diffusion-controlled limit in toluene. Femtosecond upconversion study uncovers the sub-picosecond intrinsic charge transfer timescale of the NC–NMA complex. The photoluminescence (PL) kinetics of NCs at red emission wavelengths exhibit ultrafast growth, ranging from ∼0.81 ps to ∼0.5 ps depending on λ_ex, attributed to HC relaxation. The presence of NMA further accelerates the growth kinetics to ≤0.3 ps, indicating harvesting of HCs before they fully relax to band-edge. Fluorescence correlation spectroscopy (FCS) reveals a weak interaction between NCs and NMA, resulting in a complexation reaction on a timescale of a few hundred microseconds—significantly slower than the sub-picosecond charge transfer timescale. This confirms that solvent diffusion does not limit the HC transfer rate. These findings shed light on the mechanisms of HC harvesting in CsPbI₃ NCs, offering valuable insights to enhance photovoltaic applications of red-emitting perovskite NCs.