Reprinted with permission from Santra et al. © 2013 American Chemical Society
Sequentially deposited green, orange, and red-emitting quantum dots serve as sensitizers within the titanium oxide film to render a rainbow architecture for harvesting photons from sunlight.
Using two to three layers of quantum dots, with each layer tuned to a different wavelength of the solar spectrum, a sensitized solar cell was created that efficiently converted more light than expected into energy compared with solar cells containing only one of the individual layers, providing a novel example of light management in solar cells.
The synergistic effect of layering quantum dots with varying compositions could lead to new ways to design solar cells, boosting photoconversion efficiency and increasing absorption across the solar spectrum. Less expensive to manufacture than silicon solar cells and capable of being formed into shapes and spread on surfaces, quantum dots may be an excellent option for design of the next generation of solar cells.
Capturing and managing all the photons in light is essential in building a more efficient solar cell. Current silicon solar cells capture light only in the red to near-infrared; however researchers at the Notre Dame Radiation Laboratory are attempting to build next-generation solar cells using layers of quantum dots (or tiny nanoparticles of semiconductor material) to absorb more colors, or wavelengths of light, from the visible to the infrared region of the solar spectrum. Previous methods varied the size of quantum dots to alter the wavelength of light absorbed. Rather than changing quantum dot size, the researchers varied the amount of selenium in the cadmium and sulfur dots to capture three different wavelengths of light: green, orange and red; after synthesis, the dots were deposited on a titanium oxide film one layer at a time, creating the photoanode for a tandem-layered solar cell. In their model solar cell, the power conversion efficiencies for each individual layer ranged from 1.9–2.8%. Yet, when the dots were layered, the overall power conversion efficiency was greater than the sum of the three individually layered photoanodes, reaching 40-60% higher than the estimated additive efficiencies. While the basis for the synergistic effect is being studied, the researchers postulate it may result from electrons or excitations enhancing the electron transfer process between the quantum dots in the solar cell, leading to increased power generation and a higher overall efficiency.
Prashant V. Kamat
Professor of Chemistry and Biochemistry, Radiation Laboratory, University of Notre Dame
DOE Office of Science, Division of Chemical Sciences, Geosciences, and Biosciences, Office of Basic Energy Sciences Grant DE-FC02-04ER15533
Santra, P.; Kamat, P. V., “Tandem Layered Quantum Dot Solar Cells. Tuning the Photovoltaic Response with Luminescent Ternary Cadmium Chalcogenides.” J. Am. Chem. Soc. 135, 877–885 (2013). [DOI: 10.1021/ja310737m]
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