How to make metal transparent

Silicon pillars emerge from nanosize holes in a thin gold film. The pillars funnel 97 percent of incoming light to a silicon substrate, a technology that could significantly boost the performance of conventional solar cells. Credit: Vijay Narasimhan, Stanford University

A photovoltaic cell is made by a silicon semiconductor layer sandwiched between two electrodes. The silicon layer transform the light energy carried by photons into electrical energy carried by moving electrons. In order to move, as it is the case in a battery, you need to have two conducting plates and whilst there is no problem with the one on the back of the photovoltaic cell (panel), the one on the top of the cell gets in the way of light beams decreasing the amount of light that actually hits the silicon. Reducing the size of the conducting plate increases its resistance and hence decreases the yield of the cell.

This is why the result obtained by a team of researchers in the US at Stanford is so interesting.

They have managed to manufacture silicon pillars on the top side of a photovoltaic cell in the millions. These pillars harvest the incoming light and transport it to the semiconductor layer across the conductor (made by a layer of gold).  
 Although the surface of the conductor is in the range of 60% of the overall cell surface the amount of light absorbed in the semiconductor reaches 97%. It is amazing!

The conductor level has a resistance of 20 Ohms, pretty low, and this ensures little power is wasted in the cell.

The nano-pillars are etched on the gold surface and are then coated with a silicon nitride anti-reflection layer to increase light adsorption.

In practice this results in the transparency of the conducting layer.

Author - Roberto Saracco

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