Light trapping in thin-film solar cells measured by Raman spectroscopy

In this study, Raman spectroscopy is used as a tool to determine the light-trapping capability of textured ZnO front electrodes implemented in microcrystalline silicon (µc-Si:H) solar cells. Microcrystalline silicon films deposited on superstrates of various roughnesses are characterized by Raman micro-spectroscopy at excitation wavelengths of 442nm, 514nm, 633nm, and 785nm, respectively. The way to measure quantitatively and with a high level of reproducibility the Raman intensity is described in details. By varying the superstrate texture and with it the light trapping in the µc-Si:H absorber layer, we find significant differences in the absolute Raman intensity measured in the near infrared wavelength region (where light trapping is relevant). A good agreement between the absolute Raman intensity and the external quantum efficiency of the µc-Si:H solar cells is obtained, demonstrating the validity of the introduced method.