Beneficial and constraining effects of laser scribing in buried-contact solar cells

Residual deformations of the silicon lattice following laser scribing have been shown to be present in the grooved region of buried-contact silicon solar cells. A freshly cleaved surface perpendicular to the phosphorus-diffused laser-scribed grooves has been used in conjunction with an electron beam-induced current scan to identify the regions to which the phosphorus has diffused. The presence of residual deformations/ dislocations/stress is shown to facilitate the diffusion of phosphorus to depths as large as 30 μm from the grooved wall surface. This is shown to have beneficial effects on device performance through substrate gettering for the top surface of buried-contact solar cells, but potentially detrimental effects regarding shunting of the rear floating junction where boron-diffused grooves are formed through a rear n-type layer. Solutions to the shunting of the floating junction are identified, with devices of high voltage and fill factor demonstrated. Further work is necessary to optimize the performance of these devices when used in conjunction with upright pyramids, although photolithographically defined inverted pyramids in conjunction with photolithographically defined metal contacts and a rear floating junction have been used to demonstrate an independently confirmed efficiency of approximately 22%.