Rainbow solar cells?

Physorg.com is reporting that University of Notre Dame researchers have created solar cells from different sized quantum dots, with each dot tuned to a specific wavelength of light. By arranging this quantum dots in an orderly pattern, the researchers hope they can make “rainbow” solar cells, which can then harvest a much greater range of frequencies of sunlight. Quantum dots exhibit something called the “size quantization effect.” Different sized quantum dots absorb different light frequencies – smaller dots absorb shorter wavelengths, and larger dots absorb longer wavelengths. By combining the different sized dots on one solar cell, they can create cells that absorb much more light and are much more efficient.

quantum dot rainbow solar cell
Electron transport through a structure of nanoparticles (left) and more ordered nanotubes (center) is shown. At right, different wavelengths of light can be absorbed by different-sized quantum dots layered in a rainbow solar cell. Image credit: Kongkanand, et al. ©2008 ACS.
The cells developed by the Notre Dame team used cadmium selenide quantum dots in a single layer on the surface of nano films and tubes made of titanium dioxide (Ti02). After the dots absorb the light, they inject electrons into the titanium oxide tubes, which then are collect at the electrodes to produce the current. The team is hoping to ultimately achieve efficiences in the 30% range using their quantum dot rainbow solar cells. Typical silicon based photovoltaic solar cells used in today’s solar panels operate in the 15-20% efficiency range currently.

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