Alternative contact designs for thin epitaxial silicon solar cells

Two major opportunities for increasing the performance of crystalline silic on solar cells involve reducing their thickness and reducing the losses ass ociated with their front metallic grid contacts. Front grid contacted thin epitaxial silicon solar cells based on the growth of crystalline silicon fi lms on a substrate or superstrate have been reported for many years, as hav e wafer-based solar cells with alternative contact approaches, integrating these two concepts into a single device presents an opportunity for simulta neously reducing two major loss mechanisms associated with crystalline sili con solar cells. The opportunities that exist and challenges that must be o vercome in order to realize such a device are described in this paper. The design space is defined and explored by considering a wide range of possibl e approaches. A specific approach was chosen and used to design, grow, and fabricate a proof-of-concept thin epitaxial silicon solar cell with an embe dded semiconductor grid as an alternative to a conventional front metallic grid. The work presented here has resulted in a thin epitaxial silicon sola r cell with a 7.8% designated area conversion efficiency, well isolated con tacts, negligible series resistive power loss, and less than 1% shading of the designated area. Copyright (C) 1999 John Wiley & Sons, Ltd.