High efficiency industrial screen printed n-type solar cells with front boron emitter

Abstract

There is currently much interest in n-type base cells because of potential advantages, both of silicon base material and of cell process, for high efficiency. We present results of n-base solar cells on large area multicrystalline and monocrystalline silicon wafers, produced using simultaneous diffusion of phosphorus back surface field and boron emitter, screen-printed metallization and firing through. The cell process leads to record high efficiencies of 16.4% on mc-Si and 18.3% on monocrystalline wafers. We also consider material-related cell characteristics. It is experimentally demonstrated that in mc-Si a low resistivity is correlated to reduced cell efficiency, with the optimum base resistivity lying between 1.5 and 4 Ohm-cm. By characterising and modeling cells from monocrystalline Si, from nominally clean mc-Si, as well as from intentionally Fe-contaminated mc-Si, the impact of the mc-Si wafer purity on emitter properties is investigated in more detail.