Enhanced near IR absorption in random, RIE-textured silicon solar cells: the role of surface profiles

We report on the role of surface profiles exhibiting comparable reflectance in random reactive ion etched textured Si solar cells. Internal quantum efficiency measurements demonstrate significant near IR absorption enhancement with peaks at λ ∼ 1120 nm and 1050 nm. Using Fourier analysis of random surfaces, we find a majority of spatial structures in ∼ 0.3-5-μm range. This random distribution of subwavelength periodic structures leads to enhanced oblique coupling into Si through diffractive optics mechanisms. The random surfaces supporting finer features create diffraction orders propagating at larger angles enhancing near IR absorption through oblique light propagation. Random surfaces with larger features create almost vertically propagating diffraction orders resulting in little oblique coupling, and for some structures, almost no enhanced near IR absorption.