Development of back junction point contact photovoltaic cells and arrays for space

Abstract

This paper presents the results of a project to develop back-junction, point-contact silicon solar cells and modules for space. Such cells are already fabricated commercially for terrestrial applications using standardized equipment and processes originally developed for high manufacturing throughput, low-cost semiconductor chip technologies. Individual 2 cm/spl times/2 cm cell outputs of 18%, AM0 are routinely obtained. Since all contacting takes place at the back surface, very high packing densities are possible resulting in comparatively higher output for arrays. The present study is divided into three phases: (1) development of individual cells into a space product, (2) development of rigid and flexible modules (3) and module fabrication for flight experimentation upon the Small Satellite Technology Initiative (SSTI). The first phase focused upon silicon surface and bulk features to increase photon absorption and reduce recombination. The compatibility of the finished cells with space worthy components such as interconnects and coverglasses was confirmed. In the next phase, cells were assembled into small modules. Substrate material included both rigid, 8 mil, silicon wafers as well as flexible, 1 mil Kapton. An interconnection system was developed which consisted of redundant thin-film metal patterns deposited directly on the substrate surfaces. This was followed by a solder reflow bonding process compatible with high volume robotic fabrication equipment. This effort resulted in the fabrication and testing of two SSTI flight modules consisting of a series arrangement of nine 2 cm/spl times/2 cm cells each.