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Understanding the rear-side layout of p-doped bifacial PERC solar cells with simulation driven experiments

: Wöhrle, N.; Fellmeth, T.; Greulich, J.; Bitnar, B.; Neuhaus, H.; Palinginis, P.; Köhler, R.; Rein, S.

Fulltext ()

Energy Procedia 124 (2017), pp.225-234
ISSN: 1876-6102
International Conference on Crystalline Silicon Photovoltaics (SiliconPV) <7, 2017, Freiburg>
Conference Paper, Journal Article, Electronic Publication
Fraunhofer ISE ()

To investigate the rear side of bifacial p-type Czochraslki-grown silicon PERC solar cells, the present work combines Sentaurus Device simulation - calibrated with extensively characterized samples - and the subsequent fabrication of solar cells according to the simulation findings. The authors investigate the physical alteration of rear-side characteristics in the context of an additional rear-side illumination. The additional injection represents an further factor for the balance of carrier generation, recombination and series resistances which in turn influences the design rules for the rear side layout. Our detailed bifacial simulations include these physical aspects and we derive design solutions for different bifacial illumination scenarios for a bifacial p-doped PERC solar cell. Using an industrial PERC process, solar cells with laser contact openings (LCO) and a rear aluminum grid were produced according to the simulation results with a wide variation in rear si de layout parameters. The PERC batches showed a rather constant medium (front side) efficiency of η = 20.8±0.2% and a bifaciality of 66 to 77% depending on the rear layout, allowing us to investigate the rear-side characteristics in detail and to compare them with the effects predicted by the simulations. We processed an aluminum rear contact grid with finger widths as small as 100 μm and successfully aligned it onto the LCO with 30 mu m contact openings on full-area 156x156 mm2 wafers. We reached good accordance between the monofacial measurements from front and rear side and our simulation model and could thus predict bifacial illumination results by modeling for two issues: 1. Planar rear sides have an advantage over pyramid textured rear sides for 1000 W/m front illumination unless additional rear illumination exceeds 250 W/m.