The use of ion implantation for PV application could be an innovative way of developing advanced cell structures with respect to a very simple fabrication process. Its application on p-type silicon solar cells has already showed its potential with the achievement of efficiency above 19% with selective emitter structure [1]. Nevertheless, the development of more complexes architectures like the ntype boron emitter is even more promising as the fabrication process would remain simple and the cell efficiency could be significantly improved. This study is dedicated to the achievement of high quality boron implanted emitter on textured surface. Very low emitter saturation current densities (J0e) of 80fA/cm² with implied Voc of 665mV were reached. The influence of the thermal treatment was also investigated for P-implantation. Large area solar cells (148.6cm²) on n-type Cz substrates were fabricated by co-annealing boron emitter and phosphorous BSF respectively at the front and back side of the cell. This fabrication process only requires nine processing steps which lead to a much simpler process than the conventional one made by means of single side gas diffusion. Finally, efficiencies of 16.9% were obtained with relatively poor open-circuit voltage and short-circuit current. Detailed characterization indicates a poor emitter quality which is not consistent with the saturation current density obtained on symmetrical samples. The impact of the thermal budget on the electrical properties of the wafers was investigated.
The fabrication of n-type solar cell using industrial process is presented in this study. The boron emitter was formed using novel diffusion technique with BCl 3 precursor and the passivation was made by means of dry oxidation. The influence of the grid coverage ratio on the backside was studied and an optimized value of 5% was found. Efficiencies above 19.0% were obtained on 125PSQ Cz wafers. We also report a independently certified efficiency of 18.7% measured by Callab on a special bifacial chuck. A difference in short-circuit current was observed compared to the use of a full chuck. Stability of the fabricated cell was investigated at 50°C under AM1.5 illumination. After over 100 h exposures, the cell efficiency was improved of 0.2% due to a slight increase in the V oc , leading to a maximum efficiency of 19.3%. Potential improvements in efficiency were presented by means of numerical simulations. The optimization the emitter & BSF profiles should lead to efficiency close to 20%. Finally, small modules of 2x2 cells were fabricated and measured to analyse the evolution of the cell performance at a module level. Losses in FF and current were observed will be analysed in a future work.The above text is an abstract of a manuscript initially published in the IEEE Journal of Photovoltaics.View the full manuscript at
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