Computational Study of Polaron Emission in a Lead-Halide Perovskite Nanocrystal
Aaron Forde1 , Talgat Inerbaev2,3 , Dmitri Kilin4*
1 Department of Materials Science and Nanotechnology, North Dakota State University, Fargo, North Dakota 58102, United States
2 L. N. Gumilyov Eurasian National University, Astana, Kazakhstan<
3National University of Science and Technology MISIS, 4 Leninskiy pr., Moscow 119049, Russian Federation
4Department of Chemistry and Biochemistry, North Dakota State University, Fargo, North Dakota 58102, United States
APbX3 (A=Cs,Methylammonium{MA}; X=I,Br,Cl) lead halide perovskites of various morphology are of interest for light-emitting applications due to the tuneability of their bandgap across the visible spectrum and efficient photoluminescence quantum yields (PLQYs)1,2. In the bulk morphology of MAPbI3, polaron formation is observed from infrared (IR) absorption3 and supported by computational studies4. Polaron formation inherently reduces the efficiency of interband radiative recombination in films of MAPbI3 due to the spatial separation of photo-excited electrons and holes. Alternatively, polaron formation could be exploited for efficient, low-energy intraband IR radiative transitions due to reduced electron-hole recombination rates and screened phonon interactions. CsPbX3 nanocrystals (NCs) provide an excellent framework for computational modeling of polaron formation since periodic boundary conditions can be neglected, allowing for full structural reorganization. NCs also allow investigation on the influence of confinement excited-state polaron dynamics. Using a fully-passivated CsPbBr3 NC atomistic model5-6 we compute spinor Kohn-Sham orbitals (SKSOs) with relativistic corrections and spin-orbit coupling (SOC) interaction as a basis to calculate efficiency of polaron emission. Efficiency of emission is determined from rates of non-radiative recombination (kNR) and radiative recombination (kR) as 
. kR is found from ensemble averaged oscillator strengths which are used to compute the Einstein coefficient of spontaneous emission. kNR is found from propagating the excited-state density matrix for electronic degrees of freedom, in terms of Redfield theory, which is parameterized from non-adiabatic couplings between electronic and nuclear degrees of freedom. Implications of this work could provide a framework for utilizing APbX3 materials as IR emitters/receivers for telecommunications and wireless devices or as qubits for quantum computation.
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