It is now known that solar cells should not simply be plane parallel slabs, but that they are optimized when there is a surface texture on at least one surface. This permits light trapping inside the cell. Within geometrical optics, it was long ago shown that a random texture already achieves the theoretical limit; 4n^2~~50X internal path length enhancement. Indeed, this technology is used in virtually all solar panels within the $30B/year solar cell industry in the world today. In distinction, the new generation solar cells are thin films, less than one-wavelength thick, firmly within the regime of physical optics, not geometrical optics. In this regime, no scientific limit is known for the light-trapping path-length enhancement, nor do we know the optimal surface texture. Thus we need to find the optimal surface shape for thin film solar cells within the paradigm of "Inverse Design" and mathematical "Shape Optimization". Once the ideal surface texture is mathematically determined, it is expected that all future generations of solar cells will try adopt that shape.
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