U. Gangopadhyay

Front grid design for plated contact solar cells

Front grid pattern of standard crystalline solar cells is specifically designed for screen printed silver paste contact. A detailed theoretical analysis of the proposed segmented cross grid line pattern has been carried out for optimizing the spacing and widths of the grid finger, main and sub-bus bars. It is shown that by choosing properly the grid pattern and optimizing the grid parameter, the overall front contact electrical and optical losses can be brought down to 10% or less as compared to the usual loss of 15% or more obtained with the conventional screen printed silver paste technology. Limitation of conventional screen printed contact has been pointed out. It was also observed that the total normalized power loss for segmented mesh grid with plated metal contact, the total power loss can be brought down to 10.04 percent unlike 11.57 for the case of continuous grid and plated contact.

High-density hollow cathode plasma etching for large area multicrystalline silicon solar cells

Multicrysalline silicon (mc-Si) materials are commercially important photovoltaic material. This material consists of number of grains and grain boundaries. The orientation is generally random and the size of the grain varies between a few millimeters to several centimeters. So for multicrysalline silicon, surface texturization is not possible with help of standard NaOH/KOH or other anisotropic chemical enchant. Actually texturing for enhanced absorption in silicon has been obtained by creating randomly distributed pyramids using anisotropic wet enchants, but this works well only on single crystalline silicon because of its <100> crystallographic orientation. Various surface texturization method has been used during surface preparation of mc-Si solar cell research, including mechanical grinding, laser-structuring, porous silicon etching, photolithographically defined etching etc. We developed a mask less plasma texturing technique for mc-Si solar cells using high-density hollow cathode plasma etching technique. We used SF/sub 6/ and O/sub 2/ gases in hollow cathode plasma (HCP) dry etching process. This paper demonstrates very high plasma density of 2/spl times/10/sup 12/ cm/sup -3/ at a discharge current of 20mA. Silicon etch rate of 1.3/spl mu/m/min. was achieved with SF/sub 6//O/sub 2/ plasma conditions of total gas pressure =50 mTorr, gas flow rate=40 sccm, and RF power=100W. In this paper, we also reported the surface etching characteristics of monocrystalline silicon and large area multicrystalline silicon (mc-Si) wafer.

Current Status of Layer Transfer Process in Thin Silicon Solar Cell : a review

Layer transfer process has emerged as a promising tool in the field of thin silicon solar cell technology. This process can use mono-crystalline silicon as a surface for the epitaxial growth of a thin layer of silicon. It requires some sort of surface conditioning of the substrate due to which the surface become suitable for homo-epitaxy and lift off after solar cell fabrication. The successful reuse of substrate has been reported. The use of the conditioned surface without any kind of epitaxial layer growth is also the issue to be addressed. This review paper basically describes the five most cost effective methods on which works are in progress. Several types of possible problems envisaged by different research groups are also incorporated here with necessary discussion. Work in Korea has already started in this area in collaboration IC Design and Fabrication Centre, Jadavpur University, India and that also has been mentioned.

Biracial Silicon Solar Cells with Spin-on Doping and Electroless Plating

A new method for fabrication of transistor like structure of the bifacial solar cell using spin-on doping and electroless plating has been proposed and the basic characteristics of the bifacial cell have been investigated. It is found that 9％ increase in short circuit current is achieved with bifacial connection than the unifacial connection. Some unwanted effect of the series resistance on collection efficiency under different mode of illumination has been pointed out. Loss mechanisms inherent in the transistor like bifacial structure have also been discussed.

Anti-Reflection Properties of In-Situ Doped Spin-On Film

Anti-reflection properties of post diffusion doped spin-on source (in-situ AR coating) have been investigated in some detail. A simple experiment for reflectivity study using oblique incidence of light and necessary modification of the theory of minimum reflectivity at oblique incidence has been established. The comparative study of the in-situ AR coating with available spin-on AR film on silicon Solar Cell Surface have been investigated.