Nicholas P.T. Bateman

Ion implanted metal wrap through silicon solar cells

Ion implanted emitters show reduced recombination leading to solar cells with better light collection and voltage[1]. Metal wrap through solar cells reduce shading losses and allow improved series resistance [2]. As such, the two technologies should be complementary. We present results for the first ion implanted metal wrap through cells built at Applied Materials. The cells show the expected improvement in current over baseline cells, and match the baseline voltage. Our MWT cells are limited by poor fill factor due to high series resistance. We see no difference in cell efficiency between process flows for which the hole drilling is done before texturing and before metallization, and no difference in via shunting. Our results show promise for the combination of ion implantation with MWT technology.

N-type boron emitter solar cells with implantation industrial process

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 n-type 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.

Ion-implanted high-efficiency solar cells on cast monocrystalline silicon

This paper demonstrates high-efficiency solar cells made on commercial grade cast monocrystalline (cast-mono) silicon using ion implantation. 18.9% efficient solar cells on 156 mm square cast-mono wafers from Canadian Solar are fabricated featuring an oxide passivated emitter, aluminum back-surface field and full industrial processing. Further investigation revealed that the cast-mono cells can benefit from the increased short-circuit current density due to random pyramid texture, compared to isotexture, even down to 60% area of <;100> grain on a wafer. This paper highlights the importance of improving the quality and yield of cast-mono wafers and the benefits of ion implant technology to produce high-efficiency cast-mono cells at lower cost. Also highlighted is the importance of increased light trapping from alkaline texture of cast-mono wafers.