Amit Soni

Use of chalcopyrite semiconductors CuXSe2 (X=Al, Ga and In) in solar cells: a theoretical study

The energy of sunlight falling on surface of the earth can be directly converted into electricity by means of the solar cells. Among the various materials used for photovoltaics, the chalcopyrite compounds CuXSe2 (X=Al, Ga, In) are very promising as semiconductors and have received much attention in the recent years. To check the applicability of these materials in solar cells, we have computed the energy bands, density of states, optical dielectric tensors, reflectivity, refraction and absorption coefficients using the full potential linearized augmented plane wave method. It is seen that the energy bandgap reduces from X=Al→In. The dielectric property of these materials is discussed in terms of interband transitions. The absorption coefficients of these materials in the region of solar radiation (0–5 eV energy) are discussed to explore their use in the fabrication of solar cells.

Effect of power factor improvement on switching life of self ballasted fluorescent lamps

This work aims to reveal the underlying effect of improved power factor on the life of Self Ballasted Fluorescent Lamps commonly termed as CFL. In the third world country like India because of cost effectiveness CFLs are still used without any power factor correction circuitry. Recently the power factor improvement tool is made compulsive for CFL and the recommended range as suggested by IEC 61000-3-2 is greater than 0.85. In addition to this the current harmonic distortion is preferred to be around 30% as per the standards. But unfortunately there are still CFLs available in the market which have less power factor in comparison with the desired standards. This has caused substantial problems not only on the generation side, but it certainly has considerable impact on the lamp performance. In the present work in order to exemplify this problem, four CFLs of 15W each from two different manufacturers are used for the experiment. Out of these four lamps, two lamps are ballast with low input power factor and instant start type. The other two are incorporated with improved input power factor having rapid start or warm start circuitry. The lamps are constantly switched ON and OFF at regular intervals. The interval was taken as 5 minutes ON and 5 minutes OFF. The lamps were subjected to this accelerated switching test. At the end of every switching cycle the electrode temperature was calculated from the ratio of hot resistance to cold resistance. It was thus observed that lamps with instant start ballast and poor power factor were unable to sustain the switching stress as compared to the lamps with rapid start ballast and improved power factor. Furthermore, the rise in electrode temperature for the lamps with improved power factor was within the desired standards. Thus it was concluded that lamps with poor power factor was more prone to early end in comparison with the other variety.

Electronic structure of Gd based transition metal antimonides GdTSb (T = Ni, Pt)

We report the electronic and magnetic properties of ternary GdNiSb and GdPtSb compounds with cubic MgAgAs type structure. The energy bands, density of states and atom specific magnetic moments of compounds have been computed using GGA+U approach. The calculations predict that GdNiSb is a small band gap semiconductor whereas GdPtSb is metallic in nature.We report the electronic and magnetic properties of ternary GdNiSb and GdPtSb compounds with cubic MgAgAs type structure. The energy bands, density of states and atom specific magnetic moments of compounds have been computed using GGA+U approach. The calculations predict that GdNiSb is a small band gap semiconductor whereas GdPtSb is metallic in nature.

Computational investigations of electronic and optical properties of ZnGa 2 X4 (X= S, Se): A promising solar PV material

In present paper, we discuss the first principle optoelectronic properties for ZnGa2X4 (X= S, Se) compounds. The current work have been carried out using full-potential linearized augmented plane wave (FP-LAPW) mechanism, employing density functional theory (DFT) within Perdew-Burke-Ernzerhof (PBEsol) exchange correlation approximation over Wien2k package. A direct band gap of 2.38eV and 1.51eV is found for ZnGa2S4 and ZnGa2Se4 compounds, at gama-symmetry point of Brillion zone (BZ). Moreover, optical properties like dielectric functions, absorption coefficient, refractive index, reflectivity, loss and conductivity spectra are also reported over here in order to examine their usefulness in solar cell and other optoelectronic devices.

Optoelectronic Analysis of CdGa2X4 (X= S, Se): A Promising Material for Solar Cells

In this paper, the optoelectronic nature of the CdGa2X4 (X = S, Se) solar cell materials are examined using full potential linear augmented plane wave (FP-LAPW) method as embodied in WIEN2K code. In present computation, we have used most suitable modified Backe-Johnson (mBJ) potential under the framework of density functional theory (DFT). The calculated electronic properties like energy band structure and density of states spectra show that these materials exhibit a direct band gap (Γ–Γ) result of 3.22 eV and 2.36 eV for CdGa2S4 and CdGa2Se4 compounds, respectively. Absorption spectra for CdGa2X4 (X = S, Se) compounds have been studied and it has been found that above the band gap, absorption are taking place and it covers wide visible spectrum energy range. On the basis of calculated band gap, density of states and absorption coefficient spectra, it is found that these compounds can be suitably applicable in optoelectronic devices such as solar cell. The evaluated properties pose well agreement with available experimental data.

A systematic approach to investigate electronic and optical property of CuGaS 2 using DFT

Present paper is a systematic analysis of electronic and optical properties of CuGaS2 ternary chalcopyrite semiconductor which having wide applications in area of optoelectronics. Complete knowledge of electronic structural behavior of these materials is a challenging part for researchers. All the calculations presented here are preformed using mBJ exchange correlation potential under density functional theory (DFT) framework and embodied in WIEN2K computer code. Our investigation indicates that CuGaS2 have direct band gap of 2.071eV and there absorption spectra shows good absorptive nature over wide solar spectrum range (0–5eV) which indicates suitability of this material in optoelectronic applications mostly in solar cell. All electronic and optical properties calculated in this paper poses good agreement with experimental result.

Parameters affecting the switching life in HPF self ballasted lamps

This paper explores the impact of high power factor (HPF) on the life of self-ballasted lamps or commonly referred as CFLs. In HPF CFLs the lamp current crest factor is usually very high. From the research work done so far it is well understood that the high current crest factor is detrimental for the life of lamp electrodes. The work done in this paper provides information about the filament current crest factor with corresponding change in electrode temperature. The lamps used for these experiment are switched on and off with sufficient time given to cool the lamp electrodes. The degradation of the lamp life with respect to filament current crest factor and electrode temperature are plotted and analysed. The best fit is obtained for the set of experiments conducted. From the set of results obtained a mathematical equation is derived. This work serves an important aspect of HPF circuitry and their corresponding drawback in addressing lifetime issues of CFLs.

Electronic Structure and Optical Properties of Solar Cell Materials CuAlX2 (X=S, Se)

The optical properties and electronic structure of solar cell materials CuAlX2 (X = S, Se) have been investigated in this paper by using the state-of-the-art full potential linearized augmented plane wave (FP-LAPW) method within the generalized gradient approximation (GGA) as implemented in Wien2k code. The exchange-correlation potential used in this calculation is Perdew-Burke-Ernzerhof (PBE). The optical properties such as dielectric tensor components and absorption coefficient of these materials are determined in order to investigate their usefulness as solar cell materials. Our calculations show that these compounds are direct band gap semiconductors. The optical absorption of solar radiations for CuAlSe2 is investigated to be more in comparison of CuAlS2 and hence is suggested as a useful solar cell material.

Electronic structure and optical properties of CuGaS{sub 2} and CuInS{sub 2} solar cell materials

We report energy bands, density of states and optical properties of CuGaS{sub 2} and CuInS{sub 2} chalcopyrites. The electronic structure has been computed using linear combination of atomic orbitals (LCAO) scheme within density functional theory (DFT) and full-potential linearised augmented plane wave method. The energy bands, density of states, components of dielectric tensors and absorption coefficients are compared with the available data. It is seen that the present LCAO-DFT calculations reproduce the electronic properties of both the chalcopyrites in a reasonable way. The optical properties show more absorption of solar radiations for CuGaS{sub 2} chalcopyrite, depicting its more usefulness in the solar cells. (author)