Application of Spectroscopic Ellipsometry and Infrared Spectroscopy for the Real-Time Control and Characterization of a-Si:H Growth in a-Si:H/c-Si Heterojunction Solar Cells

Abstract

AbstractWe have demonstrated real-time process control of a-Si:H growth in an a-Si:H/c-Si heterojunction solar cell by spectroscopic ellipsometry (SE). Accurate thickness control of a-Si:H p-i layers with a precision better than ± Å has been realized by this technique. From real-time attenuated total reflection spectroscopy (ATR), we find the formation of a porous interface layer with a maximum SiH2-hydrogen content of 27 at.% at the a-Si:H/c-Si interface, although a rather high conversion efficiency of 14.6 % has been obtained in the solar cell. We found that an optimum i-layer thickness for the a-Si:H/c-Si solar cells is consistent with the thickness at which the a-Si:H i-layer growth reaches a steady state after the H-rich interface-layer formation. We have applied SE further to determine the dielectric functions of In2O3:Sn and ZnO:Ga with different carrier concentrations. From the dielectric function analysis, the effective mass m is extracted. We find linear increases in m as the carrier concentration of In2O3:Sn and ZnO:Ga increases. The validity of our analyses has been confirmed from excellent agreement between carrier concentrations determined by SE and Hall measurements. The construction of the optical database further enabled us to calculate a reflectance spectrum of the a-Si:H/c-Si solar cell accurately.