Tiny, tangled wires keep photons from reflecting

Tiny, tangled wires keep photons from reflecting. The predominant material in most solar panels is shiny, crystalline silicon coated with an efficiency-improving antireflective substance. Because the Sun moves across the sky from dawn to dusk, the best antireflectors are effective for a wide range of incidence angles and for all colors of visible light. Yasha Yi and colleagues have recently devised a novel antireflecting structure with those desirable qualities. As shown in the scanning electron microscope image, the antireflecting layer consists of nanometer-thin wires that attach to the crystalline Si surface (lower edge of the figure) at random angles. The wires have a core of Si (white) and are clad with silicon oxide (gray). The varying index of refraction from cladding to core gives the wires their antireflecting properties; the random orientation of the wires makes the structure effective over a wide range of angles. To generate their tangled nanowires, the researchers heated a Si crystal and Si powder for several hours at pressures as low as 8 Pa; they then allowed the sample to cool at atmospheric pressure. Oxygen and chemistry did the rest of the work. Yi and coworkers are optimistic that their simple procedure may one day be applied to fabricate large-scale photovoltaic devices. In the short term the group hopes to create ordered structures to help them better understand the behavior of the random layers they already have in hand. (P. Pignalosa et al., AIP Adv. 1, 032124, 2011. 10.1063/1.36248382158-3226)