Effect of Al Contact Pitch on Rear Passivated Solar Cells

Abstract

In search of solar cell concepts that allow processing of thinner wafers (<150 μm), the conventional full Al rear side of p-type solar cells is replaced by an open rear metallization combined with a dielectric passivation layer. We estimate that this modification to the cell concept could result in a gain of 0.3-0.4% in absolute efficiency for a rear passivated multi-crystalline solar cell with local contacts. The gain can only be obtained when a well passivating dielectric layer is applied and Al contacts are formed with a high-quality local BSF. Three rear contacting designs are discussed: interconnected point contacts (PERC), bifacial cell with line shaped rear contacts (PASHA) and a bifacial MWT with a web pattern on both sides (ASPIRe). For these cell concepts, the performance of SiNx and Al2O3 as rear passivating layers are discussed in terms of local EQE measurements. A simple equivalent circuit is discussed to describe the parabolic LBIC pattern which is induced by inversion layer shunting between the rear metal contacts. The influence of the fixed charge density and the metallization pitch is discussed.