Drastic suppression of the optical reflection of flash-lamp-crystallized poly-Si films with spontaneously formed periodic microstructures

Polycrystalline Si (poly-Si) films formed by flash lamp annealing of precursor a-Si films on glass substrates have periodic surface roughness spontaneously formed through crystallization, which effectively acts to decrease optical reflection. The surface roughness initially decreases, and then reversely increases with increase in the duration of wet etching, performed to modulate the surface morphology and to reduce optical reflectance. This curious phenomenon can be understood as the selective removal of surface projections, which contain a number of voids, and as different etching rates of large-grain and fine-grain regions. The antireflection effect is enhanced not by the variation of the surface roughness, but rather by the removal of the voids near the surface. The etched poly-Si films covered with antireflection films show remarkably low average reflectance of 3% without any complicated texturing processes, which will lead to the fabrication of high-efficiency solar cells by a simple process.