High efficiency selective emitter enabled through patterned ion implantation

This paper discusses the benefits of patterned ion implantation to simplify process flows while enabling a road map to high efficiency cell architectures with lower cost/Watt. The ion implanted selective emitter process, named Solion Blue, is described and the results from the first test run are presented. The process integrates single sided doping with VSEAs in-situ patterned implantation technology while also incorporating a high quality thermal oxide for improved surface passivation of the emitters. The process flow is much simplified over the diffusion based process sequence since the PSG wet etch and edge isolation steps are no longer required due to ion implantation being a single-sided doping technique that forms no glass layer. An added benefit of this approach is the ease of alignment of contacts to selectively doped emitters due to the visible contrast in the differentially doped regions that enables automated optical alignment without any fiducial marks on the surface. Overall, the ion implanted selective emitter cell requires one less processing step than the standard homogeneous emitter process and results in an increase in cell efficiency of up to +1% absolute. Extensive 2D modeling, backed by experimental data, shows further optimization is possible, enabling >;19% performance from this process.