With the help of computer simulations and various advanced chip-manufacturing methods, a team of physicists and engineers at MIT have discovered new ways of getting greater efficiency from photovoltaic solar cells.
In the experiment, the team applied an anti-reflective coating to the front, and a innovative series of multi-layered reflective coatings and a defraction grating – a closely spaced array of lines – to the back of ultra-thin silicon films to increase the cells’ power by up to 50%.
With the help of the carefully designed layers on the back of each cell, light is bounced around longer inside the thin silicon film, allowing it more time to transfer its energy into an electric current. Without those coatings the light would be reflected straight out of the cell.
One of the team members, Peter Bermel, a post-doctoral researcher in MIT’s physics department explained that it is critical that any light entering the layer should travel through a long path in the silicon. But what they have not figured out yet is how long that path has to be to ensure maximum absorption of electrons to produce the electric current.
The test was started by running thousands of computer simulations, testing variations of the thickness of the silicon, spacing of the lines, and the amount and thickness of reflective layers on the back. These simulations were then used to optimize efficiency and power output.
According to Lionel Kimerling, the project manager and Thomas Lord Professor of Materials Science and Engineering: “The simulated performance was remarkably better than any other structure, promising, for 2-micrometer-thick films, a 50 percent efficiency increase in conversion of sunlight to electricity.”
Once simulations were complete, they were confirmed by actual lab-scale tests, where graduate student Lirong Zeng was given required to refine the structure and make the silicon cell. As predicted, the experiment was a success and sparked considerable industry interest.
The work done so far was just the first step toward manufacturing an affordable, improved solar cell. Now all that is needed is some fine-tuning through more simulations and lab tests, and more work on the materials and manufacturing process.
According to Kimberling, if the solar business stays strong, we can expect this new technology to be ready within the next three years. Bermel added that, “the potential for savings is great, since the high-quality silicon crystal substrates used in conventional solar cells represent about half the cost, and the thin films in this version use only about 1 percent as much silicon.”
To evaluate its business potential, the project was selected by the MIT Deshpande Center for an “i-team” study. Here it was concluded that this thin film solar cell technology could provide considerable benefits in both manufacturing and electricity production, for uses ranging from remote off-grid to dedicated clean energy.
While no single project is likely to minimize the cost of solar cells, this type of innovation takes us one step closer to making solar power design competitive with fossil fuel and nuclear grid electricity.
Originally posted 2008-11-25 12:04:44.