Rapid Thermal Processing of High Efficiency n-Type Silicon Solar Cells with Al Back Junction

In this paper we report on the design, fabrication and modeling of 49 cm², 200-μm thick, 1-5 Ω-cm, n- and p-type 〈111〉 and 〈100〉 screen-printed silicon solar cells. A simple process involving RTP front surface phosphorus diffusion, low frequency PECVD silicon nitride deposition, screen-printing of Al metal and Ag front grid followed by co-firing of front and back contacts produced cell efficiencies of 15.4% on n-type 〈111〉 Si, 15.1% on n-type 〈100〉 Si, 15.8% on p-type 〈111〉 Si and 16.1% on p-type 〈100〉 Si. Open circuit voltage was comparable for n and p type cells and was also independent of wafer orientation. High fill factor values (0.771-0.783) for all the devices ruled out appreciable shunting which has been a problem for the development of co-fired n-type 〈100〉 silicon solar cells with Al back junction. Model calculations were performed using PC1D to support the experimental results and provide guidelines for achieving >17% n-type silicon solar cells by rapid firing of Al back junction.