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Tandem colloidal quantum dot solar cells employing a graded recombination layer


Tuning of the electronic bandgap in colloidal quantum dots (CQDs) by changing their size enables the spectral response of CQD-based photodetectors1,2,3,4,5 and photovoltaic6,7,8,9,10,11,12 devices to be tailored. Multi-junction solar cells made from a combination of CQDs of differing sizes and thus bandgaps are a promising means by which to increase the energy harvested from the Sun's broad spectrum. Here, we report the first CQD tandem solar cells using the size-effect tuning of a single CQD material, PbS. We use a graded recombination layer to provide a progression of work functions from the hole-accepting electrode in the bottom cell to the electron-accepting electrode in the top cell, allowing matched electron and hole currents to meet and recombine. Our tandem solar cell has an open-circuit voltage of 1.06 V, equal to the sum of the two constituent single-junction devices, and a solar power conversion efficiency of up to 4.2%.

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Figure 1: Colloidal quantum dot (CQD) based tandem solar cells: concept and realization.
Figure 2: Design for current matching in CQD tandem cells.
Figure 3: Photovoltaic device performance for tandem and constituent single-junction cells.
Figure 4: Electrical characterization of GRL materials.


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This publication is based in part on work supported by an award (no. KUS-11-009-21) made by King Abdullah University of Science and Technology (KAUST), by the Ontario Research Fund Research Excellent Program, by the Natural Sciences and Engineering Research Council (NSERC) of Canada, Angstrom Engineering and Innovative Technology. The authors would like to acknowledge the assistance of M. Greiner and A. Fischer for UPS/XPS measurements and discussions. X.W. was partially supported by an Ontario Post Doctoral Fellowship from the Ontario Ministry of Research and Innovation. G.I.K. was partially supported by NSERC. The electron microscopy described in Supplementary Section SI1 was performed at the Canadian Centre for Electron Microscopy, which is supported by NSERC and other government agencies.

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X.W. and G.I.K. performed all device fabrication and characterization. L.L. assisted in CQD preparation. J.T., H.L., I.J.K., R.D., L.B., D.A.R.B. and S.H. assisted in GRL characterization and data analysis. X.W., G.I.K. and E.H.S. designed the experiments, interpreted the results and wrote the manuscript.

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Correspondence to Edward H. Sargent.

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Wang, X., Koleilat, G., Tang, J. et al. Tandem colloidal quantum dot solar cells employing a graded recombination layer. Nature Photon 5, 480–484 (2011).

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