Organic-inorganic hybrid halide perovskites are emerging as one of the potential materials in the photovoltaic community due to its attractive power conversion efficiency and cost-effective device fabrication. The photovoltaic performance of hybrid halide perovskite is linked to its atomic and electronic structure at the surface. Here we have used electronic structure calculations to determine the structural and electronic properties at the surface of MABX3 (MA = CH3NH3; B = Sn or Pb; X= I, Br, or Cl) perovskites. Next, we compared calculated electronic properties of the surface with the corresponding bulk values. Our results reveal that the structural properties like B-X distances, B-X-B angles, and orientation of MA are different between bulk to perovskite surface. Such changes in structural features at the perovskite surface lead to change in the band gap between surface and bulk perovskite. Both structural features and the band gap at the surface are found to be dependent on the crystal symmetry and chemistry of the perovskite. Further, for all perovskite compositions investigated, no midgap surface electronic states were observed.
The linkage between the atomic structure and the electronic property is complex for heterointerfaces involving multicomponent organic−inorganic systems because of large configurations and chemical possibilities. Understanding the structure−property relationship at the interface becomes further complicated with an asymmetric structure of organic molecules compared to the interface between planer solids. Here, we report on ab inito molecular dynamics (AIMD) simulations of the perovskite/PCBM ([6,6]-phenyl-C 61 -butyric acid methyl ester) interface, where PCBM is an asymmetric molecule. Our AIMD calculations help us to navigate the vast number of possible atomic configurations of the interface. We have found that PCBM prefers to bind with the perovskite surface via an ester moiety over its fullerene moiety. The bonding at the interface and its stability are sensitive to the chemical composition at the perovskite surface, the PbI 2 -terminated surface making a stronger binding ≈1 eV with PCBM, compared to the MAI-terminated surface. Later, we systematically studied the role of atomic defects on the perovskite surface and interface and linked it to interface stability and electronic properties.
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