Role of Cation-Anion Organic Ligands for Optical Properties of Fully Inorganic Perovskite Quantum Dots
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MRS Advances © 2018 Materials Research Society DOI: 10.1557/adv.2018.552
Role of Cation-Anion Organic Ligands for Optical Properties of Fully Inorganic Perovskite Quantum Dots
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Aaron Forde , Talgat Inerbaev , and Dmitri Kilin
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Department of Materials and Nanotechnology, North Dakota State University, Fargo ND 58108
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L.N. Gumilyov Eurasian National University, Astana 010008, Kazakhstan
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Department of Chemistry and Biochemistry, North Dakota State University, Fargo, North Dakota 58108, USA
ABSTRACT
Application of lead-halide perovskite nanostructures for photovoltaic and light emitting applications depends on fashion of the surface termination. The reasonable choice of surface ligands for perovskite nanostructures prevent formation of trap states and contribute to chemical stability, wide opening of the bandgap, and intensity of absorption and photoluminescence of perovskite nanostructures. This work provides atomistic arguments for dual ligand protocol of surface passivation of fully inorganic perovskite quantum dots with fully organic ligands being a mix of cations (ethyl-ammonium) and anions (acetic) in nearly equal proportions. Computed binding energies of either individual ligands or anion-cation pairs demonstrate high stability in comparison to thermal energy and are concluded to be favourable choice in synthesis of colloidal perovskite quantum dots for light emitting applications.
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INTRODUCTION 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 surface passivation1. Surface passivation of the QD has shown to be a major factor in PL properties, as a poorly passivated surface can introduce trap states which ultimately reduces PL quantum yields (QY) 2. Here we use Density Functional Theory (DFT) to investigate the roles of surface passivation and doping on PL emission stability of perovskite QDs. The investigated model is composed as an intrinsic QD (Cs 8Pb27Br54) terminated with 48 amines and 54 carboxylic acids to completely passivate the surface. It is found that with this surface configuration the QD requires a 2+ overall charge to have an open bandgap and for the lowest optical transition to be bright. Investigation into surface defects on electronic structure and optical properties shows that CsPbBr 3 QDs can still have bright PL with low surface defect density. It is also observed that the ligands have a strong interaction at the QD surface, resembling Coulombic interaction.
METHOD Theory: Electronic structure of the perovskite – organic dye system is found from solving the fictitious one electron Kohn-Sham (KS) equation3 from density function theory4 to construct the total density
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