Hayatullah

Bio: Hayatullah is an academic researcher from Hazara University. The author has contributed to research in topics: Electronic band structure & Band gap. The author has an hindex of 8, co-authored 12 publications receiving 188 citations.

First principle study of CsSrM3 (M=F, Cl)

Abstract: Structural, elastic, chemical bonding and optoelectronic properties of materials are important to recognize their applications in technology. In the present work CsSrM3 (M=F, Cl) are investigated to obtained their structural, elastic, chemical bonding and optoelectronic properties using the highly accurate full potential linearized augmented plane wave method. The lattice constant increases while bulk modulus decreases going from F to Cl in CsSrM3. Both the compounds are found to have indirect bandgaps. CsSrF3 is found to have a mixed bonding nature, while it is purely ionic bonding in CsSrCl3. Optical responses of the materials are calculated in terms of dielectric functions, refractive indexes, reflectivities, energy loss functions, optical conductivities and absorption coefficients. Both the materials can be used for high frequency optical and optoelectronic devices, also they can be used for transparent coatings.

Elastic and optoelectronic properties of RbMF3 (M=Zn, Cd, Hg): A mBJ density functional calculation

Abstract: Bonding nature as well as the structural, elastic, electronic and optical properties of cubic fluoroperovskites RbMF3 (M=Zn, Cd and Hg) compounds have been calculated using a full-potential augmented plane (FPLAPW) method within the density functional theory. The exchange-correlation potential was treated with the generalized gradient approximation of Wu and Cohen (WC-GGA) to calculate the total energy. Moreover, the modified Becke–Johnson potential (TB-mBJ) was also applied for the electronic and optical properties. It is found that lattice constant increases while bulk modulus decreases with the change of cation (M) in going from Zn to Hg in RbMF3 in accordance with the experimental results. The calculations of the electronic band structure, density of states and charge density show that these compounds have an indirect energy band gap (M–Г) with a mixed ionic and covalent bonding. The optical properties (namely: the absorption coefficient and the reflectivity) were calculated for radiation up to 45.0 eV.

Structural, elastic, electronic and optical properties of CsMCl3 (M=Zn, Cd)

Abstract: FP-LAPW calculations have performed in the framework of density functional theory (DFT) to compute the structural, elastic, electronic and optical properties of cubic CsMCl3(M=Cd, Zn) compounds under pressure. The generalized gradient approximation (GGA) schemes proposed by Wu and Cohen (WC) and modified Becke–Johnson (mBJ) have been utilized for these calculations. The computed GGA-lattice parameter for CsCdCl3 is in excellent agreements with the experimental data. The computed elastic constants reveal that both compounds are elastically stable and ductile in nature. Energy band structure shows that CsZnCl3 and CsCdCl3 are Γ − R indirect band gap insulators. Optical properties such as complex dielectric function, refractive index, extinction coefficient, reflectivity, energy loss function, optical conductivity and absorption coefficient for incident photon energy up to 48 eV have been predicted.

Organohalide lead perovskites for photovoltaic applications

Abstract: There are only few semiconducting materials that have been shaping the progress of third generation photovoltaic cells as much as perovskites. Although they are deceivingly simple in structure, the archetypal AMX3-type perovskites have built-in potential for complex and surprising discoveries. Since 2009, a small and somewhat exotic class of perovskites, which are quite different from the common rock-solid oxide perovskite, have turned over a new leaf in solar cell research. Highlighted as one of the major scientific breakthroughs of the year 2013, the power conversion efficiency of the title compound hybrid organic–inorganic perovskite has now exceeded 18%, making it competitive with thin-film PV technology. In this minireview, a brief history of perovskite materials for photovoltaic applications is reported, the current state-of-the-art is distilled and the basic working mechanisms have been discussed. By analyzing the attainable photocurrent and photovoltage, realizing perovskite solar cells with 20% efficiency for a single junction, and 30% for a tandem configuration on a c-Si solar cell would be realistic.

Solid-State Physics Perspective on Hybrid Perovskite Semiconductors

Abstract: In this review we examine recent theoretical investigations on 2D and 3D hybrid perovskites (HOPs) that combine classical solid-state physics concepts and density functional theory (DFT) simulations as a tool for studying their optoelectronic properties. Such an approach allows one to define a new class of semiconductors, where the pseudocubic high-temperature perovskite structure plays a central role. Bloch states and k.p. Hamiltonians yield new insight into the influence of lattice distortions, including loss of inversion symmetry, as well as spin–orbit coupling. Electronic band folding and degeneracy, effective masses, and optical absorption are analyzed. Concepts of Bloch and envelope functions, as well as confinement potential, are discussed in the context of layered HOP and 3D HOP heterostructures. Screening and dielectric confinements are important for room-temperature optical properties of 3D and layered HOP, respectively. Nonradiative Auger effects are analyzed for the first time close to the ele...

Halide-Substituted Electronic Properties of Organometal Halide Perovskite Films: Direct and Inverse Photoemission Studies

Abstract: Solution-processed perovskite solar cells are attracting increasing interest due to their potential in next-generation hybrid photovoltaic devices. Despite the morphological control over the perovskite films, quantitative information on electronic structures and interface energetics is of paramount importance to the optimal photovoltaic performance. Here, direct and inverse photoemission spectroscopies are used to determine the electronic structures and chemical compositions of various methylammonium lead halide perovskite films (MAPbX3, X = Cl, Br, and I), revealing the strong influence of halide substitution on the electronic properties of perovskite films. Precise control over halide compositions in MAPbX3 films causes the manipulation of the electronic properties, with a qualitatively blue shift along the I → Br → Cl series and showing the increase in ionization potentials from 5.96 to 7.04 eV and the change of transport band gaps in the range from 1.70 to 3.09 eV. The resulting light absorption of MA...

Electronic structure and optical band gap determination of NiFe2O4.

Abstract: In a theoretical study we investigate the electronic structure and band gap of the inverse spinel ferrite NiFe2O4. The experimental optical absorption spectrum is accurately reproduced by fitting the Tran-Blaha parameter in the modified Becke-Johnson potential. The accuracy of the commonly applied Tauc plot to find the optical gap is assessed based on the computed spectra and we find that this approach can lead to a misinterpretation of the experimental data. The minimum gap of NiFe2O4 is found to be a 1.53 eV wide indirect gap, which is located in the minority spin channel.

Electronic structure and optical band gap determination of NiFe2O4

Abstract: In a theoretical study we investigate the electronic structure and the band gap of the inverse spinel ferrite NiFe2O4. The experimental optical absorption spectrum is accurately reproduced by fitting the Tran-Blaha parameter in the modified Becke-Johnson potential. The accuracy of the commonly applied Tauc plot to find the optical gap is assessed based on the computed spectra and we find that this approach can lead to a misinterpretation of the experimental data. The minimum gap of NiFe2O4 is found to be a 1.53eV wide indirect gap, which is located in the minority spin channel.