Boston-area company Bandgap Engineering, Inc., announced it has increased the average efficiency of standard, commercial solar cells by 0.4 percentage points, from 17.2% to 17.6%, just by replacing the standard surface texture with its nanowire technology.
To demonstrate the boost, Bandgap asked a cell manufacturer to run 84 multicrystalline wafers through their standard industrial cell process, including: a standard emitter, standard silicon-nitride and standard screen printing with full back-side Al metal, on standard full-area 156 mm x 156 mm wafers. The only difference was that half the wafers in the batch had Bandgap’s patented, proprietary nanotexture, while other wafers had standard acidic texture.
“The best nanowire solar cell had 17.76% efficiency, compared to 17.32% for the best standard solar cell. Since the cell process was optimized for the standard cells, and not for nanowire cells, and since we have a clear path to further improve our technology, I expect further efficiency improvements with a fairly straightforward optimization,” added Dr. Jeff Miller, Bandgap’s Senior Device Scientist.
“This result demonstrates an efficiency benefit of nanowire solar cells over conventionally textured solar cells and demonstrates how simple and powerful an upgrade we can provide to commercial cell makers,” commented Dr. Marcie Black, president of Bandgap.
Previously, Bandgap has demonstrated even larger efficiency improvements, but the significance of this result is that the cell process was identical except for a single step, the texturing step. In previous experiments the full cell process was optimized for nanowire cells.
Separately, Bandgap also announced a new efficiency record of 19% for a monocrystalline nanowire solar cell made in collaboration with the Georgia Institute of Technology. Importantly, all the cells, including the record setting cell, were full area, 156 mm x 156 mm cells produced with a standard emitter, silicon-nitride, full back-side Al metal, and screen printed metallization.
Bandgap’s nanowire technology is a drop-in upgrade for today’s crystalline silicon manufacturers using standard processing technologies. As the technology gives low reflection for all grain orientations, it is an ideal upgrade for multicrystalline wafers, which have higher reflection. Additionally it can enable some more-advanced high efficiency and lower cost processes which are already on many manufacturer’s roadmaps. Specifically the single sided texture enables processes that require planar back surfaces for improved reflection or passivation. The low silicon consumption, less than 1 µm is consumed in the texturing process, is ideal for thin silicon technologies. Also, Bandgap has developed approaches to pattern its silicon nanowires that can enable plated front metal contacts without laser patterning or lithography.