Electrical properties of the rear contact structure of MWT silicon solar cells

• We investigate electrical properties of silver-insulator-silicon contacts on p- and n-type Cz-Si.
• Reverse bias leads to degradation of insulation of silver-insulator-silicon contact for n-type samples.
• Less impact of reverse bias stress for p-type samples observed.
• Suitable combination of paste and insulation layer shows less degradation.

In certain metal wrap through (MWT) solar cell structures, the external rear contact – that is connected to the front grid by the via contacts – directly overlaps the silicon base with opposite polarity. Since no intermediate p–n-junction is present in-between, leakage currents under forward bias may occur. Such leakage currents directly affect the conversion efficiency of the cell. This work investigates the electrical contact properties of five screen printing via pastes to p-type and n-type Czochralski-grown silicon with different surface topographies and different intermediate dielectric insulation layer systems. Dark current–voltage (IV) measurements on test structures reveal a significant impact of the via paste on the IV characteristics. In addition, especially for n-type silicon, reverse bias load leads to significantly increased forward leakage currents. Stability tests performed with p-type MWT solar cells (either with aluminum back surface field or passivated rear surface) reveal no significant fill factor drops when appropriate via pastes are used.