Evaluation of Series Resistance Losses in Screen-Printed Solar Cells With Local Rear Contacts

Abstract

We demonstrate industrially feasible large-area solar cells with passivated homogenous emitter and rear achieving energy conversion efficiencies of up to 19.4% on 125 mm × 125 mm p-type 2-3 Ω·cm boron-doped Czochralski silicon wafers. Front and rear metal contacts are fabricated by screen printing of silver and aluminum paste and firing in a conventional belt furnace. However, these cells suffer from moderate fill factors below 76% due to an increased series resistance. In this paper, we analyze the main cause of this increase. We vary the rear contact geometry over a wide range. By subtracting the respective contribution of the base from the measured series resistance, we extract a value of (55 ± 10) mΩ·cm2 for the effective specific contact resistivity of our screen-printed local aluminum rear contacts. We verify this value by local series resistance mappings from photoluminescence measurements resulting in a contact resistivity of (40 ± 10) mΩ·cm 2. Our analysis reveals that the highest potential for a further energy conversion efficiency improvement is to decrease the rear contact resistivity.