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Chen Z.,Brooklyn College | Chen Z.,The Graduate Center, CUNY | Yu C.,Brooklyn College | Yu C.,The Graduate Center, CUNY | And 7 more authors.
Journal of Luminescence | Year: 2012

We report on the determination of exciton binding energy in perovskite semiconductor CsSnI3 through a series of steady state and time-resolved photoluminescence measurements in a temperature range of 10300 K. A large binding energy of 18 meV was deduced for this compound having a direct band gap of 1.32 eV at room temperature. We argue that the observed large binding energy is attributable to the exciton motion in the natural two-dimensional layers of SnI4 tetragons in this material. © 2011 Elsevier B.V. All rights reserved.

Yu C.,Brooklyn College | Yu C.,City University of New York | Chen Z.,Brooklyn College | Chen Z.,City University of New York | And 6 more authors.
Journal of Applied Physics | Year: 2011

The temperature dependence of the bandgap of perovskite semiconductor compound CsSnI3 is determined by measuring excitonic emission at low photoexcitation in a temperature range from 9 to 300 K. The bandgap increases linearly as the lattice temperature increases with a linear coefficient of 0.35 meV K-1. This behavior is distinctly different than that in most of tetrahedral semiconductors. First-principles simulation is employed to predict the bandgap change with the rigid change of lattice parameters under a quasi-harmonic approximation. It is justified that the thermal contribution dominates to the bandgap variation with temperature, while the direct contribution of electron-phonon interaction is conjectured to be negligible likely due to the unusual large electron effective mass for this material. © 2011 American Institute of Physics.

Chung I.,Northwestern University | Song J.-H.,Northwestern University | Im J.,Northwestern University | Androulakis J.,Northwestern University | And 5 more authors.
Journal of the American Chemical Society | Year: 2012

CsSnI 3 is an unusual perovskite that undergoes complex displacive and reconstructive phase transitions and exhibits near-infrared emission at room temperature. Experimental and theoretical studies of CsSnI 3 have been limited by the lack of detailed crystal structure characterization and chemical instability. Here we describe the synthesis of pure polymorphic crystals, the preparation of large crack-/bubble-free ingots, the refined single-crystal structures, and temperature-dependent charge transport and optical properties of CsSnI 3, coupled with ab initio first-principles density functional theory (DFT) calculations. In situ temperature-dependent single-crystal and synchrotron powder X-ray diffraction studies reveal the origin of polymorphous phase transitions of CsSnI 3. The black orthorhombic form of CsSnI 3 demonstrates one of the largest volumetric thermal expansion coefficients for inorganic solids. Electrical conductivity, Hall effect, and thermopower measurements on it show p-type metallic behavior with low carrier density, despite the optical band gap of 1.3 eV. Hall effect measurements of the black orthorhombic perovskite phase of CsSnI 3 indicate that it is a p-type direct band gap semiconductor with carrier concentration at room temperature of ∼ 10 17 cm -3 and a hole mobility of ∼585 cm 2 V -1 s -1. The hole mobility is one of the highest observed among p-type semiconductors with comparable band gaps. Its powders exhibit a strong room-temperature near-IR emission spectrum at 950 nm. Remarkably, the values of the electrical conductivity and photoluminescence intensity increase with heat treatment. The DFT calculations show that the screened-exchange local density approximation-derived band gap agrees well with the experimentally measured band gap. Calculations of the formation energy of defects strongly suggest that the electrical and light emission properties possibly result from Sn defects in the crystal structure, which arise intrinsically. Thus, although stoichiometric CsSnI 3 is a semiconductor, the material is prone to intrinsic defects associated with Sn vacancies. This creates highly mobile holes which cause the materials to appear metallic. © 2012 American Chemical Society.

Shum K.,Brooklyn College | Chen Z.,Brooklyn College | Qureshi J.,Brooklyn College | Yu C.,Brooklyn College | And 5 more authors.
Applied Physics Letters | Year: 2010

We report on the synthesis and characterization of CsSnI3 perovskite semiconductor thin films deposited on inexpensive substrates such as glass and ceramics. These films contained polycrystalline domains with typical size of 300 nm. It is confirmed experimentally that CsSnI3 compound in its black phase is a direct band-gap semiconductor, consistent with the calculated band structure from the first principles. The band gap is determined to be ∼1.3 eV at point at room temperature. © 2010 American Institute of Physics.

Omnipv Inc. | Date: 2014-10-15

A photovoltaic cell includes: (1) a front contact; (2) a back contact; (3) a set of stacked layers between the front contact and the back contact; and (4) an encapsulation layer covering side surfaces of the set of stacked layers. At least one of the set of stacked layers includes a halide material having the formula: [A_(a)B_(b)X_(x)X_(x)X_(x)X_(x)][dopants], where A is selected from elements of Group 1 and organic moieties, B is selected from elements of Group 14, X, X, X, and X are independently selected from elements of Group 17, a is in the range of 1 to 12, b is in the range of 1 to 8, and a sum of x, x, x, and x is in the range of 1 to 12.

Omnipv Inc. | Date: 2014-05-22

An electro-optical device includes: (1) a first electrode layer; (2) a second electrode layer; and (3) a middle layer disposed between the first electrode layer and the second electrode layer. The middle layer includes a material having the formula: [A_(a)B_(b)X_(x)X_(x)X_(x)], where A is selected from potassium, rubidium, and cesium; B is selected from germanium, tin, and lead; X, X, and X are independently selected from fluorine, chlorine, bromine, and iodine; a is in the range of 1 to 9; b is in the range of 1 to 5; a sum of x, x, and x is in the range of 1 to 9; and the material is at least one of n-doped and p-doped.

Luminescent materials and methods of forming such materials are described herein. A method of forming a luminescent material includes: (1) providing a source of A and X, wherein A is selected from at least one of elements of Group 1, and X is selected from at least one of elements of Group 17; (2) providing a source of B, wherein B is selected from at least one of elements of Group 14; (3) subjecting the source of A and X and the source of B to vacuum deposition to form a precursor layer over a substrate; (4) forming an encapsulation layer over the precursor layer to form an assembly of layers; and (5) heating the assembly of layers to a temperature T_(heat )to form a luminescent material within the precursor layer.

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