Silicon Solar Cells and Plasmons Produce Highest Efficieny Ever

Silicon may soon find the limit of its efficiency, as miniaturization is starting to take its tall on the nanoscale properties of this wonder material, but if it is on the brink of extinction in computing technology, it may have a promising life ahead in solar cells, now at its beginnings.

These solar cells are typically made using a silicon wafer and are the dominant technology in the commercial production of solar cells, accounting for more than 86% of the solar cell market, due to the omnipresence of silicon as semiconductor in electronics.

Unfortunately, silicon is a poor light emitter and absorber and therefore solar cell efficiencies have generally been poor.

There have been some attempts to improve the electrical efficiency, but so far, experimental thin-film Si cells instead of wafer-thick have proven even poorer and the question of how to make the cells cheap but also nicely absorptive remains unanswered.

A real breakthrough has been announced by scientists at the University of New South Wales in Australia, who have now enhanced the absorption of sunlight using surface plasmons.

Surface plasmons are hybrids of the electron plasma and the photon, confined to surfaces and that interact strongly with light, like a sort of proxy for the light, except at a shorter wavelength.

If, moreover, the plasmon energy can be efficiently collected and transferred to an underlying waveguide as part of a solar cell, then the cells' yield can grow. This is what the New South Wales researchers do. They use silver nanoparticles to excite surface plasmons, which enhances light trapping.

Using 1.25-micron-thick thin-film cells, the enhancement was by a factor of 16 for light with a wavelength of 1050 nm, while when using wafers, the enhancement was by a factor of 7 for light with a wavelength of 1200 nm.

Silicon normally absorbs light only weakly in this part of the spectrum, so the enhancement is significant, at more than 33% for thin-film and 19% for wafers.

This translates into a third more energy for household appliances, fewer hours of direct sunlight needed and solar panel surface or, simply put, a third off the electricity bill.