Diffusion-free high efficiency silicon solar cells

Abstract

Traditional POCl3 diffusion is performed in large diffusion furnaces heated to ~850 C and takes an hour long. This may be replaced by an implant and subsequent 90-s rapid thermal annealing step (in a firing furnace) for the fabrication of p-type passivated emitter rear contacted silicon solar cells. Implantation has long been deemed a technology too expensive for fabrication of silicon solar cells, but if coupled with innovative process flows as that which is mentioned in this paper, implantation has a fighting chance. An SiOx/SiNy rear side passivated p-type wafer is implanted at the front with phosphorus. The implantation creates an inactive amorphous layer and a region of silicon full of interstitials and vacancies. The front side is then passivated using a plasma-enhanced chemical vapor deposited SiN xHy. The wafer is placed in a firing furnace to achieve dopant activation. The hydrogen-rich silicon nitride releases hydrogen that is diffused into the Si, the defect rich amorphous front side is immediately passivated by the readily available hydrogen; all the while, the amorphous silicon recrystallizes and dopants become electrically active. It is shown in this paper that the combination of this particular process flow leads to an efficient Si solar cell. Cell results on 160-μm thick, 148.25-cm2 Cz Si wafers with the use of the proposed traditional diffusion-free process flow are up to 18.8% with a Voc of 638 mV, Jsc of 38.5 mA/cm2, and a fill factor of 76.6%. Copyright © 2012 John Wiley & Sons, Ltd. This work presents a novel approach in utilizing implantation for silicon solar cells. First, phosphorus is implanted into textured silicon, then SiNxHy is deposited along with rear side passivation layers, then dopant activation is done using a metal-contaminated firing furnace. Cell results on 160-μm thick, 148.25-cm2 Cz Si wafers with the use of the proposed traditional diffusion-free process flow are up to 18.8% with a Voc of 638 mV, Jsc of 38.5 mA/cm2, and a fill factor of 76.6%. Copyright © 2012 John Wiley & Sons, Ltd.