Ion implanted screen printed N-type solar cell with tunnel oxide passivated back contact

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 V_oc. Process optimization resulted in high iV_oc 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 iV_oc of 727mV. The finished screen-printed 132cm² device gave a V_oc of 683mV, J_sc 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.