Impact of front and rear texture of thin-film microcrystalline silicon solar cells on their light trapping properties

Abstract

The effect of front and rear texture of thin-film microcrystalline silicon solar cells on light trapping is evaluated by characterizing solar cell specimens with both superstrate (p-i-n) and substrate (n-i-p) configurations that have a variety of surface morphologies including intentionally polished flat surfaces. It is demonstrated that the front texture enhances light absorption and external quantum efficiency from the visible region to the near-infrared region, while the rear texture increases these properties only at wavelengths longer than around 600 nm. The photocurrent enhancement by the rear texture is comparable or superior to that by the front texture, especially in n-i-p solar cells with a thin transparent conductive oxide (TCO) layer on the front surface. Irrespective of the cell configuration, parasitic absorption loss in solar cells is increased by the textures. Loss analyses show that the absorption loss at textured back-surface reflectors (BSRs) plays a dominant role in n-i-p solar cells and is obviously affected by the localized surface plasmon absorption induced by the Ag reflector with microroughness on its surface. In p-i-n solar cells, additional absorption loss due to the thick front TCO layers is superimposed on that induced by the textured BSR and becomes dominant with increasing wavelengths.