Yasuhiro Kida

Method of Removing Single-Side Doped Layer While Maintaining Pyramid Textured Surface of n-Type Bifacial Solar Cells

BBr3 and POCl3 thermal diffusion is a widely used technique for p- and n-type emitter formation in bifacial solar cell fabrication. However, single-side doping of BBr3 or POCl3 is difficult to achieve through gas diffusion carried out at high temperatures. Thus, removal of the unexpected doped layer on one side is undertaken in the fabrication of bifacial solar cells. We have implemented a spin-etching technique to remove the doped layer; however, the removal leads to a planar surface, and the related optical losses affect the bifaciality of the cell through a lowering of the short-circuit current. In this paper, we demonstrate a new procedure to maintain the pyramid texture on the side from which the doped layer is removed. The effect of the texture-maintaining removal process was examined using scanning electron microscopy (SEM) and reflectance measurements. SEM images show that the edges of the texture pyramids become wider. The optical losses due to the wider edges were investigated through reflection measurements. To investigate the potential of this new procedure, an n-type bifacial cell was fabricated on a 156 mm × 156 mm 180-μm-thick n-type pseudo Czochralski-Si wafer, and the current–voltage parameters were compared with the single-side planar n-type bifacial solar cell.

Phosphorus-Implanted Emitter Crystalline Silicon Solar Cell with AL-BSF

As-implanted local phosphorus profiles in a single texture are discussed, taking into account of the incident angle of ion beam into the pyramidal textured (111) surface. The impact of tilt and twist angle on the electrical characteristics of phosphorus-implanted homogeneous emitter silicon solar cells with aluminum back surface field, 156 × 156 mm2 in size, are investigated. Conversion efficiency increases with increase of tilt angle within a range of 7° to 35°, or decrease of rotation angle within a range of 15° to 90°. Thus, tilt and twist are the key factors of as-implantation depth profile, resulting in the improvement of conversion efficiency. Based on scanning capacitance microscopy observation, two-dimensional carrier distribution in phosphorus-implanted emitter is discussed.