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-cm2 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 Jo is dramatically reduced, resulting in much higher $V_{{\rm oc}}$ . Process optimization has resulted in high $iV_{{\rm oc}}$ of 728 mV on symmetric structures. The unmetallized cell structure with Al2O3/SiN passivated lightly doped p+ emitter and a tunnel oxide/n+ poly back also gave high $iV_{{\rm oc}}$ of 734 mV. The finished screen-printed 132-cm2 device gave a $V_{{\rm oc}}$ of 683 mV, $J_{{\rm sc}}$ of 39.4 mA/cm2, FF of 77.6%, and an efficiency of 20.9%. Cell analysis show that implementation of a selective emitter can give higher efficiency.