Electronic structure analysis of a-Si: H p-i1-i2-n solar cells using ellipsometry spectroscopy

In this study, we report an enhancement in the efficiency of a-Si:H solar cells due to the addition of an intrinsic layer. The intrinsic layer of a-Si:H p-i(1)-i(2)-n solar cells was measured by focused beam-mapping spectroscopy ellipsometry for photon energy from 0.6 to 6.5 eV. The intrinsic a-Si:H layer was made from SiH4 and H-2 by the plasma enhanced chemical vapor deposition (PECVD) technique. The Cody-Lorentz approach was identified as the best method to describe optical dispersion. The effect of hydrogen dilution on optical absorption is explained by the decrease in localized state density in the mobility gap. Furthermore, the observed structure is analyzed by adjusting the frequency derivative of the dielectric constant with the shape of the analytic critical-point line. The complex dielectric function shows good agreement with microscopic calculations for the energy shift and the broadening inter-band transitions based on the electron-hole interaction. Our results show the important role of the a-Si:H intrinsic layer in the efficiency improvement of a-Si:H p-i(1)-i(2)-n solar cells.