Ab initio calculations on CsSnX3 perovskites and mixed halides CsSn(XxY 1-x)3, X and Y = I, Cl, and Br, show that all of them have a direct band gap of ∼1 eV which can be tuned by varying the compositions of X and Y. The optimized supercells are tetragonal, orthorhombic or monoclinic. The top of the valence band arises from hybridization of Sn 4s and halogen p valence orbitals while the bottom of the conduction band has predominantly Sn p character. Similar to organo-metallic lead halides this is expected to facilitate p-p optical transitions that are highly favourable for photoabsorption. Our results suggest that these inorganic perovskites have the desired features to achieve high efficiency of photo-response with appropriate combination of halogens. © 2015 Author(s).

Vijay Kumar

Center for Informatics

Deb A.K.

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Shiv Nadar University

Ab initio design of CsSn(XxY 1−x)3 (X and Y = Cl, Br, and I) perovskites for photovoltaics

AIP Advances

Ab initio calculations on one, two, and three layers of SnS and SnSe compound semiconductors show that they all have indirect band gap similar to bulk and it varies in the range of ∼0.5–1.6 eV within the generalized gradient approximation due to quantum confinement as well as structural relaxations. In two-dimensional structures, the difference between the direct and the indirect band gap is very low and in the case of a SnS bilayer, this difference is minimum. Further, the band gaps calculated with HSE06 functional are in good agreement with the experimental results available for bulk and single layer. The total and projected densities of states show that the top of the valence band arises from the hybridization of Sn 5s and chalcogen p valence orbitals while the bottom of the conduction band has predominantly Sn 5p character. The effective mass of electrons and holes are found to be small. These features are similar to the recently discovered perovskite materials for photovoltaics with high efficiency and suggest that SnS and SnSe layered materials are also promising for photovoltaics. Further calculations on bulk and layers of GeS and GeSe are reported and the results are compared with those of SnS and SnSe structures. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Physica Status Solidi (B) Basic Research

Bandgap engineering in semiconducting one to few layers of SnS and SnSe

Chemical Communications

A facile solvothermal growth of single crystal mixed halide perovskite CH3NH3Pb(Br1−xClx)3

Advanced Materials

Unique Properties of Halide Perovskites as Possible Origins of the Superior Solar Cell Performance

Nano Letters

Atomistic Origins of High-Performance in Hybrid Halide Perovskite Solar Cells

Applied Physics Letters

Unusual defect physics in CH3NH3PbI3 perovskite solar cell absorber

J. Mater. Chem. A

Study on the stability of CH3NH3PbI3films and the effect of post-modification by aluminum oxide in all-solid-state hybrid solar cells

Ab initio design of CsSn(XxY 1-x)3 (X and y = Cl, Br, and I) perovskites for photovoltaics