Study of Low Resistivity and High Work Function ITO Films Prepared by Oxygen Flow Rates and N_2O Plasma Treatment for Amorphous/Crystalline Silicon Heterojunction Solar Cells

摘要

Pulsed DC magnetron sputtered indium tin oxide (ITO) films deposited on glass substrates with lowest resistivity of 2.62 × 10~(-4) Ω · cm and high transmittance of about 89% in the visible wavelength region. We report the enhancement of ITO work function (Φ_(ITO)) by the variation of oxygen (O_2) flow rate and N_2O surface plasma treatment. The Φ_(ITO) increased from 4.43 to 4.56 eV with the increase in O_2 flow rate from 0 to 4 sccm while surface treatment of N_2O plasma further enhanced the ITO work function to 4.65 eV. The crystallinity of the ITO films improved with increasing O_2 flow rate, as revealed by XRD analysis. The ITO work function was increased by the interfacial dipole resulting from the surface rich in O~- ions and by the dipole moment formed at the ITO surface during N_2O plasma treatment. The ITO films with high work functions can be used to modify the front barrier height in heterojunction with intrinsic thin layer (HIT) solar cells.