Abstracts Book - IMRC 2018

• SF2-O020
STRUCTURAL, ELECTRONIC, AND OPTICAL PROPERTIES OF
FORMAMIDINIUM LEAD IODIDE (FAPbI3) PEROVSKITES
DETERMINED BY FIRST-PRINCIPLES CALCULATIONS WITH VAN
DER WAALS INTERACTIONS
Karthick Sekar 1 , jose Jorge Rios Ramirez 2 , Srikanth Chakaravarthy 1 , Abdel Hadi Kassiba 3 ,
Velumani Subramaniam 2
1 Centro de Investigación y de Estudios Avanzados del IPN - CINVESTAV, Nanoscience and
Nanotechnology, Mexico. 2 Centro de Investigación y de Estudios Avanzados del IPN -
CINVESTAV, Electrical Engineering (SEES), Mexico. 3 Université du Maine, , France.
In recent years, organic-inorganic halide perovskite solar cells (OIHPSC) have
gained a critical attention in the photovoltaics field, principally, due to its
competent power conversion efficiency (PCE). Formamidinium lead iodide
(HC(NH 2 ) 2 PbI 3 or simply (FAPbI 3 ) perovskites show a broader absorption range,
larger organic cation radii, and a smaller optical bandgap compared to
methylammonium iodide (MAPbI 3 ) and cesium iodide (CsPbI 3 ). These properties
are of significant interest in its application as an absorber layer in solar cells.
However, a prominent challenge for a OIHPSC is its structural instability and
photooxidation. Therefore, better structural stability is essential to improve the
electronic and optical properties, which in turn improves the PCE. Herein, we
systematically studied the crystal structure as well as the electronic and optical
properties of FAPbI 3 perovskites by first-principles calculations based on density
functional theory (DFT) including van der Waals (vdW) interactions. The
calculations were performed over the conventional cubic Pm3m structure and
three supercell models [(2×1×1), (3×1×1), (4×1×1)] through the Cambridge serial
total energy package (CASTEP), with the generalized gradient approximation
Perdew-Burke-Ernzerhof, as the exchange-correlation functional (GGA-PBE). The
k-point mesh and the plane wave cutoff energy were chosen by carefully testing
the convergence on both, the conventional and the supercell structural
properties, and the structures were thoroughly relaxed with the Broyden-
Fletcher-Goldfarb-Schanno (BFGS) algorithm. The columbic interaction between
the FA cation with iodide the inorganic sub-cell mainly causes the displacement
of the I atoms and the reduction of the b/a & c/a ratios, thereby reaching the
known pseudo cubic structure after the optimization. The charge density
distribution among the organic FA cation and the inorganic species as well as
the 12 possible orientations of the planar FA molecule in the cubic structure play
a crucial role in the electronic, optical and stability properties of the FAPbI 3