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Improved performance and stability in quantum dot solar cells through band alignment engineering

Abstract

Solution processing is a promising route for the realization of low-cost, large-area, flexible and lightweight photovoltaic devices with short energy payback time and high specific power. However, solar cells based on solution-processed organic, inorganic and hybrid materials reported thus far generally suffer from poor air stability, require an inert-atmosphere processing environment or necessitate high-temperature processing1, all of which increase manufacturing complexities and costs. Simultaneously fulfilling the goals of high efficiency, low-temperature fabrication conditions and good atmospheric stability remains a major technical challenge, which may be addressed, as we demonstrate here, with the development of room-temperature solution-processed ZnO/PbS quantum dot solar cells. By engineering the band alignment of the quantum dot layers through the use of different ligand treatments, a certified efficiency of 8.55% has been reached. Furthermore, the performance of unencapsulated devices remains unchanged for over 150 days of storage in air. This material system introduces a new approach towards the goal of high-performance air-stable solar cells compatible with simple solution processes and deposition on flexible substrates.

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Figure 1: Photovoltaic device architectures and performance.
Figure 2: Energy level diagrams of PbS QDs and photovoltaic devices containing the QDs.
Figure 3: Evolution of photovoltaic parameters with air storage time in devices with Au and MoO3/Au anodes.
Figure 4: Long-term stability assessment of unencapsulated devices with Au anodes.

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Acknowledgements

The authors thank R. Brandt for help with the JV measurements in air, T. Buonassisi for the use of the solar simulator in air, M. Baldo for the use of the UPS system, and J. Jean for help with refractive index measurements. C-H.M.C thanks L-Y. Chang, D. Wanger, D-K. Ko, A. Maurano, I. Coropceanu and C. Chuang for fruitful discussions and technical assistance. P.R.B. was supported by the Fannie and John Hertz Foundation and the National Science Foundation. This work was supported by Samsung Advanced Institute of Technology. Part of this work made use of the MRSEC Shared Experimental Facilities at the MIT Center for Materials Science and Engineering (CMSE), supported by the National Science Foundation under award number DMR-08-19762, and the MIT Laser Biomedical Research Center (LBRC) under contract number 9-P41-EB015871-26A1, supported by the National Institute of Health.

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C-H.M.C and M.G.B. conceived and designed the project. C-H.M.C. performed most of the experiments and data analysis with some technical assistance from P.R.B. P.R.B. and C-H.M.C. performed UPS measurements and carried out their analysis. All authors discussed the results. C-H.M.C. wrote the manuscript with contributions from all authors.

Corresponding author

Correspondence to Moungi G. Bawendi.

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The authors declare no competing financial interests.

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Chuang, CH., Brown, P., Bulović, V. et al. Improved performance and stability in quantum dot solar cells through band alignment engineering. Nature Mater 13, 796–801 (2014). https://doi.org/10.1038/nmat3984

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