Probing the Multiexcitonic Dynamics in CsPbI_3 Nanocrystals across the Temperature-Induced Reversible Phase Transitions

摘要

CsPbI_3 nanocrystals (CPI NCs) have become a trending research topic due totheir impressive potential in functional optoelectronic devices and optical gainapplications. Their optical responses are governed by carrier dynamics, whichis greatly influenced by temperature and corresponding phase structure dueto the effects of inherently electron-phonon coupling. Notably, CPI NCs havebeen identified to adopt an unexpectedly stable cubic phase from roomtemperature to liquid helium temperature. Here, using in situ cryogenicelectron diffraction measurements, it is unambiguously demonstrated thatCPI NCs undergo consecutive cubic-tetragonal-orthorhombic phasetransitions from 298 to 100 K. The corresponding temperature-dependentmultiexcitonic dynamics are investigated in each phase by combiningtime-resolved photoluminescence and transient absorption spectroscopy. Inaddition to the temperature dependency, the lifetime of both excitons andbiexcitons evidently depends on the phase structures of the CPI NCs,highlighting the crucial effect of crystal structure on the carrier dynamics.Moreover, the biexciton binding energy increases with higher crystalsymmetry due to the decrease of the dielectric constant. The findings shedlight on the structural phase transition and its relationship to the carrierdynamics in all-inorganic perovskite NCs, which provides critical insight intothe structure-performance relationship in CPI NCs for promising applicationsin optoelectronic devices.