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Pat Kambhampati

Quantum Drop formation in semiconductor perovskites? Some old ideas in a new light as revealed by ultrafast spectroscopy

Mon, Sep. 25, 2023, 4:30pm
Taylor Auditorium, Frick Chemistry Lab B02
Host: Greg Scholes

Semiconductor perovskites have been under intense investigation recently for their performance in photovoltaics and recently in other optoelectronic materials. Their favorable optical performance seems to arise from some remarkable and mysterious physical processes such as defect tolerance, exciton-polaron formation, strong lattice anharmonicity, all of which give rise to a phonon glass / electron crystal which possesses liquid / solid duality. In this ionic material, the key question becomes one of complex structural dynamics giving rise to electronic properties1. Here, we monitor the electronic and structural dynamics of semiconductor perovskite nanocrystals using a suite of three ultrafast laser spectroscopies to fully characterize the life cycle of electronic excitations in perovskites. We use Two-Dimensional Electronic Spectroscopy (2DE) to monitor the first moments of coherent response which dissipates due to polaron formation2. We then use Pump/Probe spectroscopy to probe the incoherent carrier relaxation and recombination dynamics3. Finally, we use time-resolved photoluminescence spectroscopy to monitor the emission kinetics. These experiments reveal aspects of liquid-like response of the lattice which solvates charges thereby creating a confined excitonic-polaron which we refer to as a “quantum drop” in analogy to conventional quantum dots. This quantum drop has dynamical quantum confinement in which the system begins as a bulk solid and ends as a quantum confined solid. We show that these bulk nanocrystals can support strong quantum confinement effects such as strongly interacting multiexcitons. These perovskites show many spectroscopic firsts from, liquid-solid duality, to dynamical quantum confinement, to remarkable emissive properties that are unlike any other system seen in Nature to date.