In this paper, we have tried to elucidate the variation of structural, electronic, and thermodynamic properties of glasslike Na 2 GeO 3 under compressive isotropic pressure within a framework of density functional theory (DFT). The result shows stable structural (orthorhombic → tetragonal) and electronic (indirect → direct) phase transitions at P ∼ 20 GPa. The electronic band gap transition plays a key role in the enhancement of optical properties. The results of the thermodynamic properties have shown that Na 2 GeO 3 follows Debye's lowtemperature specific heat law and the classical thermodynamic of the Dulong−Petit law at high temperature. The pressure sensitivity of the electronic properties led us to compute the piezoelectric tensor (both in relaxed and clamped ions). We have observed significant electric responses in the form of a piezoelectric coefficient under applied pressure. This property suggested that Na 2 GeO 3 could be a potential material for energy harvest in future energy-efficient devices. As expected, Na 2 GeO 3 becomes harder and harder under compressive pressure up to the phase transition pressure (∼20 GPa) which can be read from Pugh's ratio (k H ) > 1.75, however, at pressures above 20 GPa k H < 1.75, which may be due to the formation of fractures at high pressure.

The saturation in increasing the power conversion efficiency (PCE) of silicon-based solar cells made researchers around world to look for the alternatives. An alternative solar cell would possess some basic requirements like cost effectiveness, reproducible, durable (stability), non-toxicity and higher efficiency. Perovskite solar cell (PSC) opened the new realm of hope for this alternative, consisting of perovskite absorber sandwich between the hole transport layer (HTL) and the electron transport layer (ETL). Good performance of PSCs can be achieved by optimizing many parameters of the components of PSC for obtaining the highest PCE. Among them, the HTL also plays a very vital role. Previously, organic poly (3,4-ethylenedioxythiophene):poly (styrene sulfonic acid) PEDOT:PSS was being widely used as the HTL in PSCs, but due to its hygroscopic nature and acidic properties, it lowered the stability and the life time of the PSCs. Later it was replaced mostly by NiO, a p-type transparent conducting oxide (TCO) enhancing the PCE of PSCs. Its excellent stability and electrical/optical properties attracted the interest of many researchers. Different types of PSCs used NiO thin films prepared from different synthesis routes and obtained variation in efficiency of PSCs. Different parameters of NiO thin films like thickness, annealing temperature (AT) and duration, precursor combinations and more in synthesis processes, have a significant role in optimizing the PCE. Though there are many routes for obtaining NiO thin film, here we are trying to focus more on sol-gel method, as this route is very cost effective and employs basic equipment. Its evolution, present status and the future perspectives will also be discussed.

Zn1-xCoxO nanoparticles have been synthesized at various concentrations of Co 2+ doping (0.005 x 0.15) by wet chemical method. Particle size was ranging from 34 -45 nm. The magnetic moment increases from x = 0.005 and 0.01 sample to x = 0.04 sample drastically showing a value of magnetic moment as high as 8.54 B/Cations and then decreases for x = 0.09 and 0.15 values of Co 2+ doping. There is almost paramagnetic behaviour for x = 0.005 and 0.01 Co 2+ doped samples. The x = 0.04 sample shows ferromagnetic ordering. Ferromagnetic behaviour decreases for x = 0.09 and 0.15 samples as the antiferromagnetic interaction dominates at higher Co 2+ doping concentrations. To probe the source of magnetism, we have undertaken photoluminescence studies also which revealed the presence of oxygen and Zinc vacancies along with other defects.

Using Density Functional Theory (DFT), 2D hexagonal silicene-ZnS-silicene trilayer heterostructure was studied with van der Waals correction as implemented in Grimme’s method. Small lattice mismatch of about 0.77% only between silicene and ZnS monolayer suggest ease in formation of sandwiched heterostructure. The negative value of total energy at 298 K from MD simulation confirms its ground state stability. Unlike monolayer silicene, our trilayer heterostructure exhibits a direct band gap of 0.63 eV in its equilibrium state. Calculated elastic moduli predict that Si-ZnS-Si has an enhanced ability to resist tensile and shear deformation than the pristine silicene and ZnS monolayer. Due to strong van der Waal’s interaction between the layers, Si-ZnS-Si has much lower thermal coefficient of linear expansion and therefore is more stable against any thermally induced deformation. When a transverse external electric field is applied, we observe direct-to-indirect band gap transition. On increasing the electric field further, the heterostructure remains indirect band gap semiconductor until it abruptly transforms to metallic nature at 1.0 V/Å. Theoretical prediction of heterostructure property presented in this work may provide valuable data for developing future nanoelectronic devices.