Contact Resistance Measurement for Thermally Diffused Point Contact by Localized Dielectric Breakdown Solar Cells

Abstract

The Point contacting by Localized Dielectric Breakdown method utilizes dielectric breakdown above a laser doped region to form ohmic contact for a solar cell rear surface. A complete cell with the laser doping process replaced with a thermal diffusion has been fabricated giving 17.5% efficiency and 0.71 fill factor. Characterization indicates that the majority of the fill factor loss is due to unexpected high contact resistance at the rear surface. In this paper, we calculate the specific contact resistivity using two different methods giving comparable results. The potential cause for these high values is discussed along with possible solutions for further improving the cell fill factor. By modulating the doping profile, the impact of surface doping concentration on contact resistivity is demonstrated. Values for contact resistivity down to $0.3 \mathrm{m}\Omega$ cm2 have been achieved on control device with surface doping concentration of $6\times 10^{19} \mathrm{cm}^{-3}$ . Low temperature annealing at 300 C is also able to improve contact resistivity to some extent.