Fully inorganic lead halide perovskite quantum dots (QDs) are of interest for optoelectronic and light emitting devices due to their photoluminescence (PL) emission properties which can be tuned/optimized by (I) surface passivation and (II) doping.Here we use Density Functional Theory (DFT) to investigate the roles of surface passivation and doping on PL emission stability of perovskite QDs. Two models are investigated: (i) an intrinsic QD (Cs8Pb27Br54) terminated with 48 amines and 54 carboxylic acids with overall charge 2+ (ii) a QD doped with Mn2+ ion (Cs8Pb26Mn1Br54) terminated with 48 amines and 54 carboxylic acids and has overall charge 2- (shown in Figure 1 below). The Mn2+ ion substitutionally replaced a Pb2+ placing it in an octahedral Br- ligand. Ground state electronic structure was determined using non-collinear DFT with PBE functional in a plane-wave basis set along with PAW pseudopotentials in VASP software. It was found that the Mn2+ dopant takes a high-spin configuration within the Br- ligand field. To account for relativistic effects of Pb2+ and Mn2+, we include spin-orbit coupling into the Hamiltonian to generate spinor Kohn-Sham (KS) orbitals. Spinor KS orbitals are used to generate non-adiabatic couplings needed to describe non-radiative relaxation of photo-excited states. Spinor KS orbitals are also used to generate oscillator strengths, which determine radiative relaxations rates, to generate time resolved and time integrated PL emission. It was found that the intrinsic QD had a six orders of magnitude higher PL intensity than the d-d optical transitions of the doped QD, in contradiction to what has been found experimentally. We suspect that our methods underestimate d-d emission of Mn2+ dopant due to the neglect of correlation. We also investigate the dynamics of spatial spin projections of excited states.

Enhanced photoluminescence quantum yield in lead halide perovskite quantum dots through doping with manganese ion: A computational study

256th National Meeting (2018)

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