A NOVEL PROCEDURE FOR FABRICATING SUB-MICRON TEXTURES ON VARIOUS THICK CRYSTALLINE-SILICON SOLAR CELLS DOWN TO 50 μm WITH LOW-REFLECTIVITY IN WIDE WAVELENGTH

摘要

Hetero-junction back-contact (HBC) solar cell is the structure realizing the highest efficiency ever obtained. For lowering the cost of crystalline-silicon (c-Si) solar cells, thinning of the original c-Si substrates is also required to reduce the material cost. In such c-Si substrates thinner than 100 μm, the optical reflection of sunlight at the back surface becomes an important key technology, and thus, texturing of the back surface is to be also important. However, in HBC solar cells, the electrode patterning must be performed on such textured back-surface. Then, small size textures should be developed for realizing both high reflectivity at the back-surface and efficient pattern-formation of the back-electrodes. Small size textures are also required for thin c-Si, since several μm size textures fluctuate the c-Si thickness itself and induce unstable performance. In the paper, it is demonstrated that the size of texture can be controlled from 10 μm or more to sub-micron by adding glass microparticles in the conventional alkaline-based texture-forming chemicals, and that such textured structures exhibited the reflectivity lower than 10% in the range of wavelength from 600 nm to 950 nm even for the 50 μm-thick c-Si substrates, before anti-reflection coating.