16 Contact Definition in Industrial Silicon Solar Cells Dr

The incredible development that industrial silicon based photovoltaic devices have followed for the last decades has been related to the consecution of a simple, easy and economically feasible way to define the electrical contacts of the devices. Due to the size of silicon photovoltaic device in relation to its substrate wafer size (one device per wafer), traditional microelectronic means to define contact (using metal evaporation in vacuum and photolithographic processes) are not economically appropriate for the mass production devices. Screen-printing technique has represented the perfect means to allow the production cost reduction, and the strong introduction of photovoltaic devices for terrestrial applications in the global market. Although similar primitive printing techniques have been known by the mankind thousand of years ago, the industrial introduction of the screen-printing technique had to wait till the end of the XIX century, beginning of the XX century. Its application in the textile industry started the beginning of its intensive use. It was in the second half of the XX century when electronic industry started to employ this technique in the field of the hybrid circuits for the deposition of dielectric and conductive layers; but its first applications in the photovoltaic industry dates from 1975-6 (Ralph, 1975); (Haigh, 1976). Since then, improvements of the screen-printing techniques and metal pastes for the creation of contacts have been crucial for the development and improvement that industrial produced silicon solar cells have followed, becoming the heart of its fabrication processes. But the technical characteristics of the screen-printed contacts are far from the ones obtained when a metal is deposited on the silicon surface with a microelectronic process in vacuum conditions, introducing limitations to the final energy conversion efficiency that devices can reach. The strong interest in increasing the conversion efficiency of industrial solar cells is encouraging the appearance of new research focused on overcoming this limitations. For this reason, advances and new developments in other techniques seem to be the future way to get improved contacts in mass production device fabrication. The application of these could mean changes in the nowadays standard processing technology that would be introduced by the industry in coming years. This chapter aims to present the curent contact definition technique, reviewing the screenprinting technology, and the ways followed to optimize its results, getting higher conversion efficiencies in devices; some design topics for the front grid patterns will be Source: Solar Energy, Book edited by: Radu D. Rugescu, ISBN 978-953-307-052-0, pp. 432, February 2010, INTECH, Croatia, downloaded from SCIYO.COM