Journal of Optoelectronical Nanostructures
Volume:6 Issue: 2, Spring 2021

In this paper, a numerical model is used to analyze an optical absorption coefficient according to the electronic properties of InGaN/GaN multiple-quantum-well solar cells (MQWSC) under hydrostatic pressure. Finite difference techniques have been used to acquire energy eigenvalues and their corresponding eigenfunctions of InGaN/GaN MQWSC and the hole eigenstates are calculated via a 6*6 k.p method under the applied hydrostatic pressure. All symmetry-allowed transitions up to the fifth subband of the quantum wells (multi-subband model) and barrier optical absorption, as well as the linewidth due to the carrier-carrier and carrier-longitudinal optical (LO) phonon scattering, are considered here. A change in the pressure up to 10 GPa increases the intraband scattering time up to 38fs and 40fs for light and heavy holes, respectively, raises the height of the Lorentz function and reduces the excitonic binding energy. The multi-subband model has a positive effect on the optical absorption coefficient and increases it by %17, contrary to the pressure function.

Nickel is a toxic transition metal which can create serious problems in health of humans and wildlife. Thus determination of nickel in environmental samples like waters is important and inevitable. In this research a simple and sensitive method for determination of nickel in water was described based on aggregation of citrate capped silver nanoparticles. Silver nanoparticles were prepared by reduction of silver nitrate with sodium borohydride. Cefixime was as chelating agent in the assay and when nickel was added to the mixture of citrate capped silver nanoparticles and cefixime, color of citrate capped silver nanoparticles changed from light yellow to red that depend on Ni2+ concentration. As a result of aggregation, local surface plasmon resonance (LSPR) band of silver nanoparticles around 395 nm decreased and a new peak appeared in 550 nm. Control experiments with 10 other ions carried out and did not a distinct change in color or spectrum. Under optimized conditions, linear relationship between Ni2+ concentrations and the absorbance ratio of A550/A395 and limit of detection were found in the range of 2.70 µmol L-1 to 17.10 µmol L-1 and 0.80 µmol L-1, respectively. The method was applied in tap and well waters that indicate the colorimetric method has acceptable accuracy and good stability.

Polythiophene is a highly conductive molecule which possesses thermal and chemical stability showing great performance in electrical devices. Polythiophene also shows an uncommon highly demanding electrical property named negative differential resistance which is a decrease of electron current with increase of applied voltage. To address this issue, in this work we study theoretically electron transport properties of a polythiophene molecular bridge sandwiched between two metal leads in the presence of Nitrogen atom as a substitute for one or two of the Carbon atoms in the molecule. The results based on Green’s function formalism show that the presence of Nitrogen reduces the electron transmission coefficient. On the other hand, Nitrogen can lead to amplification of negative differential resistance. Strength of the resistance is affected by the positions and number of Nitrogen atoms in the system. Therefore, choosing right positions for locating impurities is very important. We found that by substituting a Carbon atom with Nitrogen in some positions the system shows notable negative differential resistance. Besides, when two Carbon atoms are replaced by Nitrogen atoms there are some special locations that not only the system shows negative deferential resistance but also it works as an electronic molecular switch which is highly demanding in electronic industry.

In this study, the energy levels of spherical quantum dot (QD) and spherical quantum anti-dot (QAD) with hydrogenic impurity in the center, in the presence of spin-orbit interaction (SOI) and weak external magnetic field have been studied. To this aim, solving the Schrodinger equation for the discussed systems by using the finite difference method, the wave functions and energies of these systems are calculated. Then the effect of the external magnetic field, system radius size and height of potential barrier on the energy levels and also the linear, nonlinear and total absorption coefficients, (ACs), of the mentioned systems are studied. Numerical results show that the SOI in both models causes a split of 2p level into two sub-levels of 2p_(1/2)and 2p_(3/2) where the low index indicates the total angular momentum J. Also, considering the electron spin, under an applied magnetic field, the 1s and 2p levels split into two sub-levels and six sub-levels, respectively. Furthermore, in this research, it is proved that energy changes are significantly different as a function of radius size and height of the potential barrier in QD and QAD models and the ACs of these systems behave differently according to the incident photon energy at the same condition.

Organic-inorganic halide perovskite thin film perovskite solar cells are gaining much attention, in recent years. Designing proper electron transport layer (ETL) and hole transport layer (HTL) with high quality to achieve devices with higher efficiency are fundamental. One dimensional (1D) nanostructures are newly introduced materials with high mobility and low recombination rate, which may improve the device performance. In this paper, 1D ZnO nanorods (ZnO-NRs) as well as planar TiO2 are considered as the ETL of the device and their electrical performance are compared with different HTL materials in Sn- and Pb- perovskite. In addition, impact of critical design parameters including absorber thickness, interface defect density, back contact electrode materials on the performance of the device are comprehensively assessed. In this work, the simulations have been carries out using a 1D Solar Cell Capacitance Simulator (SCAPS-1D). The results show that in Sn- perovskite, ZnO-NRs has superior performance in comparison with TiO2 with maximum photon conversion efficiency (PCE) of 16.7 % and short circuit current density of 30.21(mA/cm2). However, in terms of Pb-perovskite planar TiO2 has given the best performance with PCE of 19.6%. The results in this paper pave the way for introducing inexpensive high performance solar cell.

In this paper, graphene oxide (GO) and its functionalization with “Amio Methyl Phosphonic Acid” (AMPA) are synthesized using modified Hummers method. Crystal structure of the compounds is investigated by X-ray diffraction pattern (XRD). Fourier transform infrared spectroscopy (FTIR) clearly shows that the AMPA agent does really enter into the GO. Transmission electron microscope (TEM) images of the compounds reveal that they are in the form of nano-sheets. High resolution TEM (HRTEM) microscope is also used to observe and study the nanoscopic morphology of the structures. In addition, the samples are element-analyzed by energy dispersive X-ray spectroscope (EDS), and X-ray photoelectron spectroscopy (XPS) to get more information. Finally, the functionalization mechanism of GO with AMPA is studied and the mechanisms of “nucleophilic displacement” as well as “condensation reaction” are suggested andare experimentally confirmed. Due to the favorable properties of the synthesized material AMPA-GO, its use was suggested for water treatment and removal of heavy metals such as lead and strontium.

 The performance characteristics of InGaN double-quantum-well (DQW) laser diodes (LDs) with different last barrier structures are analyzed numerically by Integrated System Engineering Technical Computer Aided Design (ISE TCAD) software. Three different kind of structures for last quantum barrier including doped- GaN, doped- AlGaN and GaN/AlGaN superlattice last barrier are used and compared with conventional GaN last barrier in InGaN-based laser diodes. Replacing the conventional GaN last barrier with p-AlGaN increased hole flowing in the active region and consequently the radiative recombination which results in the enhancement of output power. However it caused increasing the threshold current due electron overflowing. For solving this problem, the last barrier structure altered with GaN/AlGaN superlattice. The simulation indicates that the electrical and optical characteristics of LDs with the superlattice last barrier, like output power, differential quantum efficiency (DQE) and slope efficiency, has significantly improved, besides the threshold current decreased. The enhancement is mainly attributed to the improvement of hole injection and the blocking electron overflowing which are caused by the reduction of polarization charges at the interface between the barrier and well, and electron blocking layer (EBL).