Development of chip-size silicon solar cells

SunPower is developing a novel 250-Sun concentrator module that, because of a compact nonimaging optics design, is very low profile and looks much like a conventional flat plate module. This "micro-concentrator" requires very small, "chip-size" solar cells, with approximate dimensions of 2.3/spl times/2.3 mm. The authors have adapted their all-back point-contact silicon solar cell technology to this application. This cell technology has several advantages over competing Ill-V technologies including lower cost, elimination of grid shading, and more tolerance of nonuniform and off-normal cell illumination due to all-backside carrier collection and texture, respectively. A major problem for such small silicon cells, however, is the efficiency loss due to the sawed edges of the cell. An "edge surface field" created by a through-wafer diffusion is one possible solution to the problem. Modeling and preliminary experimental results are presented.