Silicon solar cells efficiency improvement with Nano Imprint Lithography technology

•NIL process over silicon multi crystalline solar cells.•Average reflectivity lower than 3% without anti-reflective coating.•A gain of 0.33% absolute efficiency is obtained on the Si-mc Nano-imprinted cell compared to the KOH textured Si-mc cell.

A large scale patterning processes to produce patterned silicon surfaces with low reflectivity were developed for silicon solar cells. Optical design, sample manufacturing, optical characterizations and cell efficiency measurements were conducted. Optical simulations were carried out to compute the reflectivity of the patterned surface to target the optimum shape to be manufactured in the silicon substrate. Patterned surfaces were manufactured using thermal Nano Imprint Lithography over 125 × 125 mm2 Si-c and Si-mc wafer and proportional dry etching. A high aspect ratio inverted pyramid shapes were achieved in both Si-c & Si-mc substrates. An effective reflectivity (Rw) of about 3% was achieved on multi-crystalline silicon with the inverted pyramid pattern. The patterning process uniformity over the substrate was better than 97%. I(V) measurements of standard Si-mc KOH textured and Si-mc inverted pyramidal textured using Nano imprint and dry etching revealed that a drop of about 3% were induced in the open-circuit voltage, a drop of about 3.4% for the fill factor, however with an increase of about 8.3% for the short-circuit current. A gain of 0.33% absolute efficiency is obtained on the Si-mc Nano-imprinted cell compared to the KOH textured Si-mc cell. The gain of the short-circuit current is directly connected to the gain of reflectivity (8%) obtained on the finished solar cell.

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