Laser-processed High-efficiency Silicon Rise-ewt Solar Cells And Characterisation

摘要

The RISE-EWT (Rear Intendigitated Single Evaporation Emitter Wrap Through) solar cell is a silicon wafer-based solar cell concept that is capable of achieving solar energy con-, version efficiencies of over 21%. The fabrication sequence is based exclusively on industrially feasible processing steps and avoids any photolithography and masking steps, nor does it require boron diffusion. For low process complexity, the RISE-EWT solar cell can be made with only a single phosphorus diffusion and a single evaporation step for metallisation. All structuring of the cell is based on non-contacting laser processing. Laser technology is the key tool for processing RISE-EWT solar cells: The cell has laser drilled and phosphorus-diffused holes to connect the emitter layer on the front side with the emitter and the contacts on the rear side. The emitter and base contact regions are defined by laser ablation of a diffusion barrier and KOH etch prior to phosphorus diffusion. An important feature of RISE-EWT solar cells are steep surface features (flanks) that are produced by the laser ablation and KOH-etching. We use these flanks to achieve reliable separation between the contacts to the n-type polarity and to the p-type polarity of the solar cell. We provide a description of RISE-EWT manufacturing process and present an analysis of the recombination losses in our cells.