High efficiency n-silicon solar cells using rear junction structures

This paper reports two near junction structures for n-silicon solar cells. They are respectively rear totally- (PERT) and rear locally-diffused (PERL) junction cells. The electrical contacts are deployed on both sides of the cells with n- on the front and p- on the rear, most surface area being passivated by silicon dioxide. A shunt problem in the rear PERL structure, resulting in a low fill factor, has been identified and solved by using the different contact characteristics of PtSi/p-silicon and PtSi/n-silicon. Open-circuit voltages up to 694 mV are obtained for the rear PERT structure, and 696 mV for the PERL. Both of the rear junction n-silicon solar cells have achieved high energy conversion efficiencies of 21.9% and 21.2% respectively. The results were measured at one Sun (0.100 W/cm² ), global AM 1.5 spectrum, 25°C by Sandia National Laboratories. Some front junction n-silicon cells have also been fabricated to compare with the rear junction cells. The measured results have shown that the open-circuit voltage for the front junction cells is about 34 mV lower than the rear junction cells. The reason for this is discussed