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ACS Nano. 2015 Nov 24;9(11):11286-95. doi: 10.1021/acsnano.5b04917. Epub 2015 Oct 7.

Highly Efficient Copper-Indium-Selenide Quantum Dot Solar Cells: Suppression of Carrier Recombination by Controlled ZnS Overlayers.

Kim JY1, Yang J2,3, Yu JH2,3, Baek W2,3, Lee CH4, Son HJ1, Hyeon T2,3, Ko MJ1,4.

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Photo-Electronic Hybrids Research Center, Korea Institute of Science and Technology (KIST) , Seoul, 136-791, Republic of Korea.
Center for Nanoparticle Research, Institute for Basic Science (IBS) , Seoul, 151-742, Republic of Korea.
School of Chemical and Biological Engineering, Seoul National University , Seoul, 151-742, Republic of Korea.
KU-KIST Graduate School of Converging Science and Technology, Korea University , Seoul, 136-701, Republic of Korea.


Copper-indium-selenide (CISe) quantum dots (QDs) are a promising alternative to the toxic cadmium- and lead-chalcogenide QDs generally used in photovoltaics due to their low toxicity, narrow band gap, and high absorption coefficient. Here, we demonstrate that the photovoltaic performance of CISe QD-sensitized solar cells (QDSCs) can be greatly enhanced simply by optimizing the thickness of ZnS overlayers on the QD-sensitized TiO2 electrodes. By roughly doubling the thickness of the overlayers compared to the conventional one, conversion efficiency is enhanced by about 40%. Impedance studies reveal that the thick ZnS overlayers do not affect the energetic characteristics of the photoanode, yet enhance the kinetic characteristics, leading to more efficient photovoltaic performance. In particular, both interfacial electron recombination with the electrolyte and nonradiative recombination associated with QDs are significantly reduced. As a result, our best cell yields a conversion efficiency of 8.10% under standard solar illumination, a record high for heavy metal-free QD solar cells to date.


ZnS overlayers; copper−indium−selenide; heavy metal-free; quantum dot-sensitized solar cells; recombination control


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