Point- and planar-junction p-i-n silicon solar cells for concentration applications

Several designs of silicon concentrator cells having a front metal grid are evaluated and compared in terms of performance, fabrication complexity and stability under concentrated sunlight. The highest beginning of life performance corresponds to a front-gridded-point-junction cell that has achieved a 26% efficiency at 90 suns. This performance relies on the quality of the interface between the undoped silicon and the silicon dioxide that covers most of the surface and it degrades upon exposure to concentrated light. A good compromise between stability and performance has been achieved with a modified Point-Junction design that incorporates a phosphorus diffusion at the front surface; the p+ points are imbedded in this planar n+ region. Some experimental results for simplified p-i-n designs with planar dopant diffusions are also presented. Finally, a modeling comparison between front-gridded p-i-n and back- junction cells is established that points out the superiority of the latter