Role of Inter-Particle Connectivity In the Photo-Carrier Cooling Dynamics and Coherent Nonlinear Interactions in Perovksite Quantum Dot Solids

The surface chemistry and inter-connectivity of perovskite nanocrystal assemblies play a critical role in determining the electronic characteristics and interactions[1]. They manifest in the Coulomb screening of electron–hole correlations and the carrier thermalization dynamics, among other many-body processes. Here, we characterize the role of inter-particle coupling in ultrafast photo-excitation dynamics in a ligand-free formamidinium lead bromide quantum dot solids. We observe that the inter-particle connectivity has deterministic effects on the many-body interactions that are relevant for carrier thermalization. These include carrier-carrier interactions that result in Auger-reheating of the carriers, and lattice characteristics that subsequently affect the phonon-assisted cooling dynamics. Independently, we also measure and analyse the coherence dynamics of these material systems using two-dimensional spectroscopy. We report the presence of Fano-like interference between the discrete excitonic states and the carrier continuum. We identify the spectroscopic signatures of a coupled exciton-carrier excited state, which provides a quantitive estimate of strength of exciton-carrier interactions. Our results highlight the presence of coherent coupling between exciton and free carriers, particularly in the sub-100 femtosecond timescales, which drives ultrafast carrier cooling in these QD solids [2]. This spectroscopic study of ultrafast carrier dynamics in perovskite QD solids establishes inter-dot separation as a critical material design parameter for the optimization of photo-generated carrier temperature and excitonic properties, which fundamentally determines the luminescence characteristics and thus the opto-electronic quality of the material.<br/><br/>[1] David O. Tiede, Carlos Romero-Pérez, Katherine A. Koch, K. Burak Ucer, Mauricio E. Calvo, Ajay Ram Srimath Kandada, Juan F. Galisteo-López, Hernán Míguez, Effect of connectivity on the carrier transport and recombination dynamics of perovskite quantum dot networks, ACS Nano, 18, 2325-2334 (2024).<br/>[2] E. Rojas-Gatjens, D. O. Tiede, K. A. Koch, C. Romero-Perez, J. F. Galisteo-Lopez, M. E. Calvo, H. Miguez, A. R. Srimath Kandada, Exciton-carrier coupling in a metal halide perovskite nanocrystal assembly probed by two-dimensional coherent spectroscopy, Journal of Physics: Materials 7, 025002 (2024).