Abstract
We present a simple industrially upscaleable process for the fabrication of bifacial n-type silicon solar cells. A process simplification is achieved by simultaneous diffusion of phosphorus back surface field (BSF) and boron emitter in one single high temperature process, the so called co-diffusion. A borosilicate glass (BSG) layer, deposited by atmospheric pressure chemical vapor deposition (APCVD) and an atmosphere containing POCl3 in an industrial tube furnace serve as dopant sources. We show that the oxygen concentration in the furnace during diffusion affects the boron surface concentration. This is a simple method to avoid boron rich layer formation and adjust the emitter sheet resistance. The doping profile of the phosphorous diffused BSF is controlled by adjusting the N2-POCl3 gas flow during diffusion allowing for independent manipulation of profile depth and surface concentration. For very high concentrations of POCl3 in the atmosphere during diffusion significant diffusion of phosphorus into the boron emitter, the so called cross doping, is observed. By lowering the POCl3 concentration cross doping can be reduced below the measurement accuracy.
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