Ion-Implanted Screen-Printed n-Type Solar Cell With Tunnel Oxide Passivated Back Contact

Abstract

This paper shows the results and the limitations of a 21% N-Cz 239-cm ² screen-printed cell with blanket p ⁺ emitter and n ⁺ back surface field. In addition, we show the properties and impact of tunnel oxide capped with doped n ⁺ polysilicon and metal on the back side, which can overcome those limitations. Since both the doped n ⁺ layer and the metal contact are outside the bulk silicon wafer, the J _o is dramatically reduced, resulting in much higher V _oc . Process optimization has resulted in high iV _oc of 728 mV on symmetric structures. The unmetallized cell structure with Al ₂ O ₃ /SiN passivated lightly doped p ⁺ emitter and a tunnel oxide/n ⁺ poly back also gave high iV _oc of 734 mV. The finished screen-printed 132-cm ² device gave a V _oc of 683 mV, J _sc of 39.4 mA/cm ² , FF of 77.6%, and an efficiency of 20.9%. Cell analysis show that implementation of a selective emitter can give higher efficiency.