Mrinal Dutta

A novel and simple method to grow beaded nanochains of ZnO with superior photocatalytic activity

We have demonstrated a novel and simple low-cost method to grow beaded nanochains of ZnO using an aqueous chemical growth method. Whatman filter paper (40) is used as the template. The filter paper is generally made up of cellulose fibers along which the growth of beaded ZnO nanoparticles (NPs) is initiated. When the filter paper is burnt at 700 degrees C temperature, the NPs appear as a beaded nanochain morphology while those synthesized without the filter paper form lumped nanostructures without any regular shape and size. A model has been proposed to explain the growth mechanism. A sharp and strong green emission has been observed for the template-grown sample in contrast to a broad and less intense hump of the without template-grown sample. The beaded nanochains shows 64% photocatalytic degradation of methyl orange (MO) under UV irradiation, which is much superior to a value of only 22% shown by the lumped sample. Not only can this low-cost simple template-based synthesis be applied to grow other nanostructures of similar morphology but is also promising for enhancing the properties in the multifunctional materials.

High Efficiency Hybrid Solar Cells Using Nanocrystalline Si Quantum Dots and Si Nanowires.

We report on an efficient hybrid Si nanocrystal quantum dot modified radial p-n junction thinner Si solar cell that utilizes the advantages of effective exciton collection by energy transfer from nanocrystal-Si (nc-Si) quantum dots to underlying radial p-n junction Si nanowire arrays with excellent carrier separation and propagation via the built-in electric fields of radial p-n junctions. Minimization of recombination, optical, and spectrum losses in this hybrid structure led to a high cell efficiency of 12.9%.

Effect of Cu Doping in the Structural, Electrical, Optical, and Optoelectronic Properties of Sol-Gel ZnO Thin Films

The effect of Cu doping (0.08-4%) on the structural, electrical, optical, and optoelectronic properties of sol-gel ZnO thin films deposited on glass substrates have been investigated. X-ray diffraction studies show that the doped films are single-phase wurtzite structure with random orientations. A decreasing trend in the c-axis parameter up to 0.5% is observed followed by an increasing trend above that. Field-emission scanning electron microscopy shows a grain texture. The energy dispersive spectroscopy as well as the film color confirms the Cu doping. Optical transmittance measurements show 80% transparency in the visible region for the films up to 0.3% Cu content. The doped films become very resistive as indicated by the four probe electrical resistivity and current-voltage measurements. The photoluminescence spectra reveal with Cu doping, a green emission at 515 nm appeared and the UV peak intensity at 376 nm is drastically lowered. However, no green emission is observed as the doping is increased beyond 0.5%. The changes in the structural, electrical, and optical properties are correlated to interstitials defects. The photoconductivity studies show that the UV sensitivity of the films is enhanced up to 0.1%, which indicates that the films can be used as UV sensors.

Quenching of Photoluminescence in ZnO QDs Decorating Multiwalled Carbon Nanotubes

We report the controlled growth of ZnO quantum dots (QDs) on the sidewalls of multiwalled carbon nanotubes (MWCNTs) by a one-step process and study the effect on the photoluminescence (PL) properties of the ZnO QDs-MWCNT composite. The PL intensity of the composite is quenched and the lifetime is reduced compared to the only ZnO QDs. The origin of the PL quenching is discussed in terms of energy transfer, which is examined by varying the density and size of ZnO QDs by changing the molar concentration of the precursor solution for ZnO and the amount of MWCNT.

Effect of nanowire length on the performance of silicon nanowires based solar cell

Currently, silicon nanowires (SiNWs) are attracting attention as promising candidate materials for developing the next-generation solar cells to realize both low cost and high efficiency due to their unique structural, electrical, and optical properties. In this paper, a vertical-aligned SiNWs array has been prepared by metal-assistant chemical etching technique and implemented on SiNW array textured solar cells for photovoltaic application. The shape and size of SiNWs were controlled by etching time of 30 min, 45 min and 60 min with the length of SiNWs of 4 μm, 6 μm and 8 μm, respectively. The etching rate was estimated to be about 133 nm per minute. The optical properties of a SiNWs array with different lengths were investigated in terms of optical reflection property. Less than 6% reflection ratio from 300 nm to 800 nm wavelength was achieved. In addition, I–V characteristic was used to estimate the dependence of the SiNWs length on the performance of SiNWs based solar cell. Conservation efficiencies were achieved of 1.71%, 2.19%, and 2.39% corresponding to 4 μm, 6 μm and 8 μm SiNWs in length, respectively.

Functionalization of Silicon Nanostructures for Energy-Related Applications

Silicon (Si) is used in various application fields such as solar cells and electric devices. Functionalization of Si nanostructures is one way to further improve the properties of these devices such as these. This Review summarizes recent results of solar cell and Li-ion battery applications using Si-related nanostructures. In solar cell applications, the light trapping effect is increased and the carrier recombination rate is decreased due to the short carrier collection path achieved by radially constructed p-n junction in Si nanowires, resulting in higher power conversion efficiency. The nonradiative energy transfer effect created by nanocrystalline Si is a novel way of improving solar cell properties. Si-related nanostructures are also anticipated as new anode materials with higher capacity in Li-ion batteries. Si-related nanocomposite materials which show densely packed microparticle structures agglomerated with small nanoparticles are described here as a promising challenge. These unique structures show higher capacity and longer cycle properties.

Si Nanowire Solar Cells: Principles, Device Types, Future Aspects, and Challenges

Dream of low-cost and high-efficiency Si solar cells is going to see daylight through the advent of Si nanowire (SiNW)-based solar cells due to the unique three-dimensional structures over planar solar cells. SiNW arrays are designed to increase light absorption beyond the bandgap limitations by efficient light trapping and antireflection. Junction fabrication technique has made it possible to make very short carrier collection pathways that provide the opportunity to use lower-grade Si material and also reduce material quantity while maintaining high-quality photovoltaic performance. Additionally, peeling off and transfer of SiNW arrays or in situ growth of SiNWs directly on low-cost substrates can introduce another major cost reduction in photovoltaic industry. This chapter focuses on the recent progress and photovoltaic aspects of the state-of-the-art technologies for SiNW-based solar cell fabrication. Fabrication and performance of different types of photovoltaic devices based on SiNWs are summarized. The challenges face by the fabrication processes and drawbacks of these kinds of devices due to the use of SiNWs are also discussed. Several possible new techniques to face the problems of this emerging field are also included.