Role of Pb2+ Adsorbents on the Opto-Electronic Properties of a CsPbBr3 Nanocrystal: A DFT Study

Fully inorganic lead halide perovskite nanocrystals (NCs) are of interest for photovoltaic and light emitting devices due to optoelectronic properties. Understanding the surface chemistry of these materials is of importance as surface defects can introduce trap-states which reduce their functionality. Here we use Density Functional Theory (DFT) to model surface defects introduced by Pb 2+ on a CsPbBr 3 NC atomistic model. Two types of defects are studied: (i) an under-coordinated Pb 2+ surface atom and (ii) Pb 2+ atomic or molecular adsorbents to the NC surface. From the DFT calculations we compute the density of states (DOS) and absorption spectra of the defect models to the pristine fully-passivated NC model. We observe that for the low surface defect regime explored here that neither (i) or (ii) produce trap-states inside of the bandgap and exhibit bright optical absorption for the lowest energy transition. From the models studied, it was found that the Pb 2+ atomic absorbent provides broadening of the conduction band edge, which implies chemisorption of Pb 2+ to the NC surface. At higher defect densities it would be expected that Pb 2+ atomic absorbents would introduce trap-states and degrade the opto-electronic properties of these materials.