Skip to main content

Thank you for visiting You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

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


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.

Your institute does not have access to this article

Access options

Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

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.


  1. Graetzel, M., Janssen, R. A. J., Mitzi, D. B. & Sargent, E. H. Materials interface engineering for solution-processed photovoltaics. Nature 488, 304–312 (2012).

    CAS  Article  Google Scholar 

  2. Wadia, C., Alivisatos, A. P. & Kammen, D. M. Materials availability expands the opportunity for large-scale photovoltaics deployment. Environ. Sci. Technol. 43, 2072–2077 (2009).

    CAS  Article  Google Scholar 

  3. Zarghami, M. H. et al. p-Type PbSe and PbS quantum dot solids prepared with short-chain acids and diacids. ACS Nano 4, 2475–2485 (2010).

    CAS  Article  Google Scholar 

  4. Tang, J. et al. Colloidal-quantum-dot photovoltaics using atomic-ligand passivation. Nature Mater. 10, 765–771 (2011).

    CAS  Article  Google Scholar 

  5. Ip, A. H. et al. Hybrid passivated colloidal quantum dot solids. Nature Nanotech. 7, 577–582 (2012).

    CAS  Article  Google Scholar 

  6. Choi, J. J. et al. Photogenerated exciton dissociation in highly coupled lead salt nanocrystal assemblies. Nano Lett. 10, 1805–1811 (2010).

    CAS  Article  Google Scholar 

  7. Semonin, O. E. et al. Peak external photocurrent quantum efficiency exceeding 100% via MEG in a quantum dot solar cell. Science 334, 1530–1533 (2011).

    CAS  Article  Google Scholar 

  8. Johnston, K. W. et al. Schottky-quantum dot photovoltaics for efficient infrared power conversion. Appl. Phys. Lett. 92, 151115 (2008).

    Article  Google Scholar 

  9. Pattantyus-Abraham, A. G. et al. Depleted-heterojunction colloidal quantum dot solar cells. ACS Nano 4, 3374–3380 (2010).

    CAS  Article  Google Scholar 

  10. Luther, J. M. et al. Stability assessment on a 3% bilayer PbS/ZnO quantum dot heterojunction solar cell. Adv. Mater. 22, 3704–3707 (2010).

    CAS  Article  Google Scholar 

  11. Zhao, N. et al. Colloidal PbS quantum dot solar cells with high fill factor . ACS Nano 4, 3743–3752 (2010).

    CAS  Article  Google Scholar 

  12. Tang, J. et al. Quantum junction solar cells. Nano Lett. 12, 4889–4894 (2012).

    CAS  Article  Google Scholar 

  13. Rath, A. K. et al. Solution-processed inorganic bulk nano-heterojunctions and their application to solar cells. Nature Photon. 6, 529–534 (2012).

    CAS  Article  Google Scholar 

  14. Chang, L-Y., Lunt, R. R., Brown, P. R., Bulović, V. & Bawendi, M. G. Low-temperature solution-processed solar cells based on PbS colloidal quantum dot/CdS heterojunctions. Nano Lett. 13, 994–999 (2013).

    CAS  Article  Google Scholar 

  15. Ning, Z. et al. Graded doping for enhanced colloidal quantum dot photovoltaics. Adv. Mater. 25, 1719–1723 (2013).

    CAS  Article  Google Scholar 

  16. Yuan, M. et al. Doping control via molecularly engineered surface ligand coordination. Adv. Mater. 25, 5586–5592 (2013).

    CAS  Article  Google Scholar 

  17. Jean, J. et al. ZnO nanowire arrays for enhanced photocurrent in PbS quantum dot solar cells. Adv. Mater. 25, 2790–2796 (2013).

    CAS  Article  Google Scholar 

  18. Soreni-Harari, M. et al. Tuning energetic levels in nanocrystal quantum dots through surface manipulations. Nano Lett. 8, 678–684 (2008).

    CAS  Article  Google Scholar 

  19. Jasieniak, J., Califano, M. & Watkins, S. E. Size-dependent valence and conduction band-edge energies of semiconductor nanocrystals. ACS Nano 5, 5888–5902 (2011).

    CAS  Article  Google Scholar 

  20. Brown, P. R. et al. Energy level modification in lead sulfide quantum dot thin films through ligand exchange. ACS Nano (2014).

  21. Shrotriya, V., Li, G., Yao, Y., Chu, C-W. & Yang, Y. Transition metal oxides as the buffer layer for polymer photovoltaic cells. Appl. Phys. Lett. 88, 073508 (2006).

    Article  Google Scholar 

  22. Meyer, J. et al. Transition metal oxides for organic electronics: Energetics, device physics and applications. Adv. Mater. 24, 5408–5427 (2012).

    CAS  Article  Google Scholar 

  23. Gao, J. et al. n-type transition metal oxide as a hole extraction layer in PbS quantum dot solar cells. Nano Lett. 11, 3263–3266 (2011).

    CAS  Article  Google Scholar 

  24. Brown, P. R. et al. Improved current extraction from ZnO/PbS quantum dot heterojunction photovoltaics using a MoO3 interfacial layer . Nano Lett. 11, 2955–2961 (2011).

    CAS  Article  Google Scholar 

  25. Gao, J. et al. Quantum dot size dependent JV characteristics in heterojunction ZnO/PbS quantum dot solar cells. Nano Lett. 11, 1002–1008 (2011).

    CAS  Article  Google Scholar 

  26. Greiner, M. T. et al. Universal energy-level alignment of molecules on metal oxides. Nature Mater. 11, 76–81 (2012).

    CAS  Article  Google Scholar 

  27. Meyer, J., Shu, A., Kröger, M. & Kahn, A. Effect of contamination on the electronic structure and hole-injection properties of MoO3/organic semiconductor interfaces. Appl. Phys. Lett. 96, 133308 (2010).

    Article  Google Scholar 

  28. Irfan, et al. Energy level evolution of air and oxygen exposed molybdenum trioxide films. Appl. Phys. Lett. 96, 243307 (2010).

    Article  Google Scholar 

  29. Hines, M. A. & Scholes, G. D. Colloidal PbS nanocrystals with size-tunable near-infrared emission: Observation of post-synthesis self-narrowing of the particle size distribution. Adv. Mater. 15, 1844–1849 (2003).

    CAS  Article  Google Scholar 

  30. Beek, W. J. E., Wienk, M. M., Kemerink, M., Yang, X. & Janssen, R. A. J. Hybrid zinc oxide conjugated polymer bulk heterojunction solar cells. J. Phys. Chem. B 109, 9505–9516 (2005).

    CAS  Article  Google Scholar 

Download references


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.

Author information

Authors and Affiliations



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.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Supplementary information

Supplementary Information

Supplementary Information (PDF 4096 kb)

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

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).

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI:

Further reading


Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing