The structural, electronic, optical, and thermal properties of mixed-halide MAPbBrxI3-x and SbH4PbBrxI3-x (x = 0-3) perovskites are investigated using first-principles density functional theory and machine-learned force fields (MLFF). A crucial element of this work is the rigorous validation of the MLFF approach against the well-established MAPbBrxI3-x benchmark system, which confirmed the method's high fidelity in reproducing the experimentally established relative thermal-stability trends of the MA-based benchmark. Formation-energy calculations revealed that bromine incorporation significantly enhances thermodynamic favorability relative to the binary precursor phases in both series, with SbH4PbBr3 exhibiting the most favorable formation energy (-0.078 eV). MLFF molecular dynamics simulations demonstrated that Br-rich SbH4PbBrxI3-x alloys (x >= 2) maintain crystalline integrity within the 100 ps simulation window up to 500 K, while iodine-rich phases undergo structural collapse at elevated temperatures due to insufficient entropic stabilization. Electronic-structure analyses at the PBE+vdW and HSE+SOC+vdW levels showed that SbH+4 substitution systematically narrows the band gap by 0.13-0.35 eV relative to MA-based counterparts, yielding HSE+SOC+vdW values of 1.29-1.88 eV across the composition series. At the spin-orbit-coupled level, the computed band-edge splittings contain an artificial ferroelectric component arising from the ordered molecular orientations of the finite supercells; they are therefore not interpreted as intrinsic bulk Rashba parameters and are noted only as a qualitative, methodology-controlled comparison between the two A-site chemistries. Optical spectra computed within the PBE+SOC+Delta framework demonstrated strong and broad visible-light absorption with a reduced blue-shift compared to MA-based analogs, confirming that SbH+4 substitution preserves spectral coverage despite bromide incorporation. Among all investigated compositions, SbH4PbBr2I emerges as a computationally promising candidate warranting experimental investigation, combining an HSE+SOC+vdW band gap of 1.71 eV in the useful range for wide-gap photovoltaic absorbers with crystalline integrity within the simulation timescale up to 500 K and strong visible-light absorption. These results computationally demonstrate that SbH4PbBrxI3-x represents a candidate hydride-based perovskite family that, if it proves synthetically accessible, could help address the stability-efficiency trade-off inherent to iodide-rich compositions.

This paper comparatively investigates the structural and electronic properties of hybrid perovskites MAPbBr_xI_1-x and SbH_4PbBr_xI_1-x by means of DFT-based calculations. The main aim is to check if the increase in band gap due to substitution of I^- ions with Br^- ions can be overcome by introducing the inorganic SbH_4^+ cation. Since the Br^- ions merely enhance structural stability of the perovskite framework and SbH_4^+ not only sustains that stability but also reduces the band gap to nearly ideal values and thereby improves electronic performance, these are the leading candidates among them. Of them, the reduced band gap SbH_4PbI_3 (∼1.37 eV) and the perfectly matched SbH_4PbBrI_2 with its band gap being exactly 1.51 eV are top prospects for being stable and having high-efficiency solar cell applications. The findings show that SbH_4^+-based perovskites have potential for future photovoltaic devices.

This paper comparatively investigates the structural and electronic properties of hybrid perovskites MAPbBr$_x$I$_{1-x}$ and SbH$_4$PbBr$_x$I$_{1-x}$ by means of DFT-based calculations. The main aim is to check if the increase in band gap due to substitution of I$^-$ ions with Br$^-$ ions can be overcome by introducing the inorganic SbH$_4^+$ cation. Since the Br$^-$ ions merely enhance structural stability of the perovskite framework and SbH$_4^+$ not only sustains that stability but also reduces the band gap to nearly ideal values and thereby improves electronic performance, these are the leading candidates among them. Of them, the reduced band gap SbH$_4$PbI$_3$ ($\sim$1.37 eV) and the perfectly matched SbH$_4$PbBrI$_2$ with its band gap being exactly 1.51 eV are top prospects for being stable and having high-efficiency solar cell applications. The findings show that SbH$_4^+$-based perovskites have potential for future photovoltaic devices.

Sahip olduğu elektronik özelliklerden dolayı Çinko Oksit (ZnO) yeni nesil güneş pillerinde kullanılan önemli malzemelerdendir. Ancak saf ZnO’nun güneşten gelen ışınlar ile çalışma veriminin arttırılması gerekmektedir. Yabancı atomlar ile katkılama bu anlamda önemli tekniklerden biridir. Bu çalışmada ZnO kristalinin Se atomu ile katkılanması teorik olarak incelenmiştir. Hesaplamalarda yoğunluk fonksiyoneli teorisi (YFT) kullanıldı. Ancak teorinin bilinen hatalarını düzeltmek için hesaplamalarda YFT+U düzeltmesi yapıldı. Bu metot ile saf ZnO’nun bant aralığı 3.27 eV değerinde hesaplandı. Bu değer deneysel değer olan 3.44 eV değerine yakındır. Se atomu kristal yapı içerisinde yerel bozulmalara yol açmaktadır. Ancak bu bozulmalar ZnO kristalinin karakteristik özelliklerini kayda değer değiştirmemektedir. Se ile katkılama esas olarak elektronik yapıda değişime yol açmaktadır. Daha fazla değerlik elektronuna sahip Se ile Zn atomu yer değiştirdiğinde bant aralığında, valans bant maksimumunun üzerinde safsızlıktan kaynaklanan iki dolu enerji seviyesi oluşmaktadır. Oluşan bu enerji seviyeleri ZnO’nun görünür bölgedeki ışığın absorpsiyonu aktivitesini artırmaktadır. Elde edilen diğer bir önemli veri ise Se katkılı ZnO kristalinde oksijen eksikliğinin olmasının görünür bölgedeki absorpsiyon aktivitesini olumlu yönde etkilemesidir.

Perovskites are organic-inorganic compounds with a crystal structure that revolutionize many optoelectronic applications, especially solar cells. The CsPbBr3−xIx, a perovskite, has garnered significant attention due to its tunable band gap and excellent photovoltaic properties. In this theoretical study, the structural, electronic, and optical properties of CsPbBr3−xIx are investigated through density functional theory calculations. The calculations reveal that the substitution of Br with I leads to a significant reduction in the band gap of CsPbBr3−xIx, resulting in improved light absorption properties. The obtained data show that the coexistence of Br and I ions in the structure creates an energy level similar to the shallow energy levels caused by doping at the R symmetry point in the band structure.

The hybrid halide perovskite CH$_3$NH$_3$PbI$_3$ is easy to manufacture and inexpensive. Despite these, its efficiency as a solar cell is comparable to today's efficient solar cells. For these reasons, it is attracting a lot of attention today. However, the effects of the CH$_3$NH$_3^+$ (MA) molecule in the perovskite structure on the electronic and structural properties are still a matter of debate. Previous studies have generally focused on the rotation of the MA molecule. In this study, from a different perspective, the effects of the movement of the MA molecule along the C-N axis are investigated. With this method, the effects of the MA molecule were examined in a more controlled way. In this study, density functional theory (DFT) that accounts for van der Waals (vdW) interactions was used in the calculations for the cases. According to the data obtained, H-I ionic bonds are formed between the MA molecule and the inorganic framework. Within the structure, the H-I bond length tends to be preserved, although the position of the MA changes. In this mechanism, the I ion plays an important role by moving away from its place in the Pb-I-Pb alignment. The position of the I ion determines the nature of the band gap transition. Another effect is on the value of the band gap. Depending on the position of the I ion, the band gap may narrow by about 0.26 eV. The separation of the I ion from the Pb-I-Pb alignment by the effect of the MA molecule breaks the inverse symmetry. According to the data obtained from this study, this mechanism in the band gap is due to the breaking of the inverse symmetry in the crystal structure.

In this study, the structural, electronic and optical properties of Pb doped rutile SnO2 were investigated using the range separated hybrid exchange-correlation functional method. In the calculations, LDA functional was used instead of PBE functional. The electronic structure of SnO2 obtained by this method is quite compatible with the experimental data. The SnO2 has an important usage area in optoelectronic devices due to its transparent and conductive nature. One of these important areas is the use of SnO2 as an electron transport layer (ETL) in perovskite solar cells. Therefore, the energy level of the conduction band of the SnO2 is important. In the Pb doped SnO2 cases, the band gap narrows as the Pb doping rate increases. The bandgap of SnO2 can be narrowed from 3.60 eV to 3.02 eV with a %12.5 Pb doping ratio, and this narrowing is proportional to the amount of Pb. The calculation results obtained in this study show that the decrease in the energy level of the bottom of the conduction band plays an important role in the narrowing of the band gap and there is no significant change in the energy level of the top of the valence band. Due to this effect of the Pb atom, the energy level of the conduction band can be adjusted by using the doping ratio of the Pb atom and the band gap can be narrowed in a controlled manner. With the Pb doping, the energy levels of the SnO2 ETL can be adjusted in a range according to the type of perovskite used in solar cell. In addition, the doping with Pb does not create electron traps in the band gap, which is important in the transport process of electrons.

In this study, oxygen vacancies and adatoms have been considered on the surface of both hexagonal and triangular ZnO nanowires. Their effect on the electronic structure and optical spectra of the nanowires have been investigated using the exact exchange hybrid density functional theory calculations. A surface oxygen vacancy gives rise to appearance of a band gap state at almost 0.7 eV above the valence band of the both types of the nanowires while an oxygen adatom show bulk-like electronic properties. A shape dependence is also indicated by the calculated physical quantities of oxygen related point defects on ZnO nanowires.

We studied the electronic and atomic structures of anatase TiO2 codoped with Cr and N using hybrid density functional theory calculations. The nonlocal screened Hartree-Fock exchange energy is partially mixed with the traditional semilocal exchange energy. This not only patches the bandgap underestimation but also improves the description of the anion/cation-driven impurity states and the magnetization of the dopants. Cr and/or N doping modifies the valence and conduction band edges of TiO2, leading to significant bandgap reduction. Hence, Cr, N and Cr-N doped TiO2 are promising for enhanced visible light absorbance.

We studied the electronic and atomic structures of anatase TiO2 codoped with Cr and N using hybrid density functional theory calculations. Nonlocal screened Hartree-Fock exchange energy is partially mixed with traditional semilocal exchange part. This not only heals the band gap underestimation but also improves the description of anion/cation-driven impurity states and magnetization of the dopants. Cr and/or N doping modifies the valence and conduction band edges of TiO2 leading to significant band gap reduction. Hence, Cr, N and Cr-N doped TiO2 are promising for enhanced photoactivity.

Electronic properties and atomic structures of W, N, S, W/N, and W/S dopings of anatase TiO_2 have been systematically investigated using the density functional theory (DFT). The exchange and correlation effects have been treated with Heyd, Scuseria and Ernzerhof (HSE) hybrid functional. Mixing traditional semi-local and non-local screened Hartree-Fock (HF) exchange energies, the HSE method corrects the band gap and also improves the description of anion/cation derived gap states. Enhanced charge carrier dynamics, observed for W/N codoped titania, can partly be explained by the passivative modifications of N 2p and W 5d states on its electronic structure. Following this trend we have found an apparent band gap narrowing of 1.03 eV for W/S codoping. This is due to the large dispersion of S 3p states at the valance band (VB) top extending its edge to higher energies and Ti--S--W hybridized states appearing at the bottom of the conduction band (CB). W/S-TiO_2 might show strong visible light response comparable to W/N codoped anatase catalysts.

The adsorption profiles and electronic structures of Pt-n(n = 1-4) clusters on stoichiometric, reduced and reconstructed rutile TiO2(110) surfaces were systematically studied using on site d-d Coulomb interaction corrected hybrid density-functional-theory (DFT) calculations. The atomic structure of small Pt cluster adsorbates mainly depends on the stoichiometry of the corresponding titania support. The cluster shapes on the bulk terminated ideal surface look like their gas phase low-energy structures. However, for instance, they get significantly distorted on the reduced surfaces with increasing oxygen vacancies. On nonstoichiometric surfaces, Pt-Ti coordination becomes dominant in the determination of the adsorption geometries. The electronic structure of Pt-n/TiO2(110) systems cannot be correctly described by pure DFT methods, particularly for nonstoichiometric cases due to the inappropriate treatment of the correlation for d electrons. We performed DFT + U calculations to give a reasonable description of the reconstructed rutile (110) surface. Pt clusters induce local surface relaxations that influence band edges of titania support and bring a number of band-gap states depending on the cluster size. Significant band gap narrowing occurs upon Pt-n-surface interaction due to adsorbate driven states on the bulk terminated and reduced surfaces. On the other hand, they give rise to a band-gap widening associated to partial reoxidation of the reconstructed surface. No metallization arises even for Pt-4 on rutile.