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 239cm2 screen printed cell with blanket p+ and n+. 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 Voc. Process optimization resulted in high iVoc of 728mV on the symmetric structures. The un-metallized cell structure with Al2O3/SiN passivated lightly doped p+ emitter and a tunnel oxide / n+ poly back also gave high iVoc of 727mV. The finished screen-printed 132cm2 device gave a Voc of 683mV, Jsc of 39.4mA/cm2, FF of 77.6% and an efficiency of 20.9%. Cell analysis show that implementation of a selective emitter can give higher efficiency.