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Metal-Assisted Chemistry for Anti-Reflection Etching of Silicon

Stage: Development

One major problem for energy conversion in solar cells is the loss of solar energy due to the high refractive index of silicon. An effective way to reduce the reflective property of silicon is through surface texturing, or etching, which may improve the amount of photon absorption in the cell and therefore either increase its power output, or enable the use of thinner (and therefore less-expensive) devices.

NREL scientists have patented methods to etch the Si wafer to have nanoscale pores at room temperature. These pores help angle light reflected from the Si surface into the cell, increasing the rate of exciton generation. This decrease in overall surface reflectivity makes the silicon wafer appear to be black. This Black Silicon has been proven to reduce the reflectivity level of silicon from the standard 11% (with ARC) all the way down to 2%.

While previous attempts at etching Black Silicon surfaces have used Au and Ag nanoparticles, researchers at the National Renewable Energy Lab, NREL, have developed a way to utilize copper when etching a nanoporous black silicon surface. Using Cu to etch silicon is advantageous because Cu is orders of magnitude less expensive than Au or Ag, is more soluble when mixed with silicon, and is already compatible with standard industrial processes used in Si microfabrication facilities. Moreover, while Au and Ag nanoparticles can also be detrimental to the cell due to their diffusion potential, this problem is eliminated by use of Cu nanoparticles. 

For more information, contact Bill Hadley at Bill.Hadley@nrel.gov

ROI 12-18

Applications and Industries

  • High Efficiency Solar Cells
  • Solar Energy Industry


  • Using copper to etch nanoporous silicon reduces costs
  • Compatible with existing industrial technologies
  • Using copper is less detrimental to the silicon solar cell than using gold or silver
  • Lowers reflectivity of the solar cell