S. Kalainathan

Dielectric, etching and Z-scan studies of glycine doped potassium thiourea chloride crystal

Abstract Glycine doped potassium thiourea chloride (PTC) crystal has been grown by slow solution evaporation technique. The dielectric studies have been employed to examine substantial improvement in dielectric constant and dielectric loss of glycine doped PTC crystal. The etching studies have been performed to investigate the surface quality of this crystal. The z-scan studies have been carried out at 632.8 nm to explore the third order nonlinear optical nature. The negative nonlinear refraction of glycine doped PTC crystal was found to be of 7.27 × 10−12 cm2/W. The origin of high magnitude of third order nonlinear optical susceptibility and reverse saturable nonlinear absorption have been investigated. The obtained results were explored to discuss the nonlinear optical applications of PTC crystal.

Performance enhancement of thin film silicon solar cells based on distributed Bragg reflector & diffraction grating

The influence of various designing parameters were investigated and explored for high performance solar cells. Single layer grating based solar cell of 50 μm thickness gives maximum efficiency up to 24 % whereas same efficiency is achieved with the use of three bilayers grating based solar cell of 30 μm thickness. Remarkably, bilayer grating based solar cell design not only gives broadband absorption but also enhancement in efficiency with reduced cell thickness requirement. This absorption enhancement is attributed to the high reflection and diffraction from DBR and grating respectively. The obtained short-circuit current were 29.6, 32.9, 34.6 and 36.05 mA/cm2 of 5, 10, 20 and 30 μm cell thicknesses respectively. These presented designing efforts would be helpful to design and realize new generation of solar cells.

Design and optimization of ultrathin crystalline silicon solar cells using an efficient back reflector

Thin film solar cells are cheaper but having low absorption in longer wavelength and hence, an effective light trapping mechanism is essential. In this work, we proposed an ultrathin crystalline silicon solar cell which showed extraordinary performance due to enhanced light absorption in visible and infrared part of solar spectrum. Various designing parameters such as number of distributed Bragg reflector (DBR) pairs, anti-reflection layer thickness, grating thickness, active layer thickness, grating duty cycle and period were optimized for the optimal performance of solar cell. An ultrathin silicon solar cell with 40 nm active layer could produce an enhancement in cell efficiency ∼15 % and current density ∼23 mA/cm2. This design approach would be useful for the realization of new generation of solar cells with reduced active layer thickness.

Performance evaluation of thin film silicon solar cell based on dual diffraction grating

Light-trapping structures are more demanding for optimal light absorption in thin film silicon solar cells. Accordingly, new design engineering of solar cells has been emphasized and found to be effective to achieve improved performance. This paper deals with a design of thin film silicon solar cells and explores the influence of bottom grating and combination of top and bottom (dual) grating as a part of back reflector with a distributed Bragg reflector (DBR). Use of metal layer as a part of back reflector has found to be promising for minimum requirement of DBR pairs. The effect of grating and anti-reflection coating thicknesses are also investigated for absorption enhancement. With optimization, high performance has been achieved from dual grating-based solar cell with a relative enhancement in short-circuit current approximately 68% while it was approximately 55% in case of bottom grating-based solar cell. Our designing efforts show enhanced absorption of light in UV and infrared part of solar spectrum.

Design and Analysis of Thin Film Based Silicon Solar Cells for Efficient Light Trapping

Silicon based solar cells are still preferable due to its existing technology with inexpensive fabrication cost. However, silicon solar cells are having drawback of weak absorption in longer wavelength due its indirect band gap and needs efficient light trapping in active region. In this paper, we present a design of solar cells based on top anti-reflection coating (ARC) layer and back reflector which is composed of distributed Bragg reflector (DBR) and diffraction grating (GRA) using finite difference time domain (FDTD) method. Simulations show efficient trapping of photon in active region as comparison to reference solar cell. A relative enhancement of cell efficiency ~54 and 60 % is observed for designed solar cells C2 and C3 respectively. This enhancement in performance of solar cells is attributed to the increased absorption and quantum efficiency in red and infrared part of incident solar spectrum.

Dielectric relaxation in CoFe2-xYxO4 (x=0.2, 0.4, 0.6) prepared by hydrothermal method

Yttrium substituted cobalt ferrite (CoFe2−xYxO4) powders (x = 0.2, 0.4 and 0.6) have been synthesized by hydrothermal method. X-ray diffraction has revealed the single phase formation of the compound with impurity phase formation at higher yttrium doping. Dielectric relaxations were observed due to the presence of oxygen vacancies and Maxwell–Wagner effect. The activation energies calculated from the impedance spectra confirmed that oxygen vacancies were the causes for dielectric relaxation. Doping of yttrium has suppressed the magnetic saturation due to the decrease of Fe3+–Fe3+ interactions.