New insights gained through pilot production of high‐eficiency silicon solar cells

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Abstract
Examination of results from the pilot production of buried‐contact solar cells (BCSC) allows several new insights into the effects of the substrate resistivity, the differences between upright and inverted pyramid texturing, the reflection after encapsulation and the doping level at which the emitter begins to dominate the overall recombination. A lower substrate resistivity in conjunction with thicker wafers reduces the effects of a high back surface recombination velocity and allows both higher voltages and efficiencies. In BCSCs with low substrate resistivities, the voltage is not limited by the back but by the emitter diffusion and the dislocation formation at the surface. Contrary to previous reports, best results have been realized with upright pyramids rather than inverted pyramids. In addition, the relative performance of the upright pyramids improves after encapsulation owing to the less than optimal unencapsulated reflection of these surfaces in the regions of the pyramid peaks where oxide layers are too thin to gain benefits as an antireflection layer. Recent results also indicate that the contributions to the dark saturation current from both the heavily phosphorus‐diffused region beneath the metal contact and the more lightly diffused top surface emitter are less than indicated previously. Finally, comparison between experimentally obtained voltages and those predicted through modelling with PC‐1D provides an estimate of the bulk material lifetimes in the pilot line cells.

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