Design of selective emitter profiles for high efficiency solar cells under manufacturing technology constraints

Fabrication and analysis of a 21% efficient baseline n-PERT cell in this paper revealed that its performance was limited by its large J₀ values on the front and back side, highlighting the need for a bifacial structure with selective emitters to decrease J₀. To determine the practical efficiency limit of such a cell, Sentaurus 2-D modeling was conducted using doping profiles previously reported for high efficiency cells. The maximum efficiency was calculated to be 22.7% with self-alignment of the contacts to the heavily doped regions. Modeling was then conducted to investigate the losses incurred from the required alignment tolerances associated with the heavily doped region and metal contacts made with today's large-scale manufacturing equipment. Through careful design of the selective emitter and back surface field doping profiles, we show that for 50 μm wide metal contacts screen printed on a 300 μm wide heavily doped region on a 10 Ω-cm base wafer with bulk lifetime of 3 ms, the loss can be decreased by 0.65%, with practical screen-printed cell efficiencies approaching 22.5%. Projected future technology improvements show efficiencies up to 23% are possible with this structure.