Fabrication of monolithic photovoltaic arrays on crystalline silicon by wafer bonding and deep etching techniques

Abstract

In this work, a novel technology to fabricate small (∼1 cm2) c-Si photovoltaic mini-modules is shown. This technology combines two main bulk micro-machining techniques: fusion (or adhesive) bonding and anisotropic etching of silicon. Due to the fact that the photovoltaic cells are fabricated in the same wafer, it is mandatory to etch the whole substrate to ensure electrical isolation. Once the individual cells are bulk-isolated they can be connected in series so as to scale up the output voltage of the mini-array. A handling wafer is required to provide mechanical stability to the device wafer. Adhesive and fusion bonding are used to join the handling and the device wafer. First electrical results, under standard Air Mass 1·5 (AM 1·5) solar spectrum light (100 mW/cm2), using a 9-cell series connected mini-module fabricated by fusion bonding, leads to a total open-circuit voltage of 4·11 V, a short-circuit current of 2·45 mA, and a maximum delivered power of 3·8 mW for each mini-module (1·4 cm2). A 16-cell series-connected mini-module fabricated by adhesive bonding and wire bonding, yields an open-circuit voltage of 7·45 V, a short-circuit current of 390 µA, and maximum delivered power of 1·8 mW, with 1·1 cm2 of mini-module area. Copyright © 2005 John Wiley & Sons, Ltd.