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. (I) Surface passivation of the QD affects PL capabilities, as an under-passivated surface can introduce trap states which reduces PL quantum yields (QY). (II) Doping quantum dots with transition metal ions provides stable optical transitions as a way to evade this issue. Doping perovskite QDs with Mn2+ ions provides high intensity 4T1 -&gt;6A1 optical transitions in addition to the bright, intrinsic QD emission. Here we use Density Functional Theory (DFT) to investigate the roles of surface passivation and doping on PL stability of perovskite QDs. Two models are investigated: (i) a pristine QD (Cs8Pb27Br54) terminated with 48 amines and 54 carboxylic acids with overall charge 2+ (ii) a QD doped with Mn2+ ion (Cs8Pb26Mn1Br54) terminated with the same ligands and has overall charge 2+. The Mn2+ ion substitutionally replaced a Pb2+ placing it in an octahedral Br- ligand field. Ground state electronic structure was determined using non-collinear DFT with PBE functional. It was found that the Mn2+ dopant takes a high-spin S=5/2 configuration within the Br- ligand field. To account for relativistic effects of Pb2+ and Mn2+ on optical properties, we include spin-orbit coupling into the Hamiltonian to generate spinor Kohn-Sham orbitals (SKSO). SKSOs are used to generate non-adiabatic couplings needed to describe non-radiative relaxation of photo-excited states. SKSOs 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 orders of magnitude higher PL intensity than the d-d optical transitions of the doped QD, in contradiction to experiment. We suspect that our methods underestimate d-d emission of Mn2+ dopant due to the neglect of e- - e- correlation. We also investigate the dynamics of spatial spin projections of excited states.

Role of surface passivation and doping on photoluminescence quantum yield in lead halide perovskite quantum dots

256th National Meeting (2018)

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