NREL Unveils Black Silicon Etching Technique for Solar Cells

September 07, 2010 by Jeff Shepard

The U.S. Department of Energy’s National Renewable Energy Laboratory (NREL) has unveiled a new low-cost etching technique which it says can put a trillion holes in a silicon wafer the size of a compact disc.

The "Black Silicon" Nanocatalytic Wet-Chemical Etch emerged from work by NREL photovoltaic researchers that demonstrated that "black silicon" solar cells, which have been chemically etched to appear black, can better absorb the sun’s energy. According to NREL, the inexpensive, one-step method reduces light reflection from silicon wafers to less than 2%, and promises to reduce manufacturing production cost and capital expense.

Any photons reflected from the surface of a solar cell are wasted. To reduce reflected sunlight and increase cell efficiency, NREL scientists invented the antireflection process that turns silicon wafers black so they absorb 98% of solar radiation. Today’s solar cells absorb about 95% of the sun’s radiation.

According to NREL, the much-lower-cost recipe is still a few tenths of a percent less efficient than the best of the conventional cells. However, the black silicon prevents reflection of low-angle morning and afternoon sunlight far better, which means a jump in photovoltaic efficiency of at least 1 percentage point can be achieved. Black silicon also would replace a process that uses dangerous and environmentally unfriendly gases. A switch to the simple black silicon process also would reduce a factory’s capital costs by about 10%.

NREL’s Howard Branz is the principal scientist for the black-silicon etch technology, working with postdoctoral researcher Hao-Chih Yuan, research scientist Matthew R. Page, senior research technician Vernon E. Yost, senior scientist Scott Ward and engineer Anna Duda.