Air-stable n-type colloidal quantum dot solids

Abstract

Colloidal quantum dots (CQDs) offer promise in flexible electronics, light sensing and energy conversion. These applications rely on rectifying junctions that require the creation of high-quality CQD solids that are controllably n-type (electron-rich) or p-type (hole-rich). Unfortunately, n-type semiconductors made using soft matter are notoriously prone to oxidation within minutes of air exposure. Here we report high-performance, air-stable n-type CQD solids. Using density functional theory we identify inorganic passivants that bind strongly to the CQD surface and repel oxidative attack. A materials processing strategy that wards off strong protic attack by polar solvents enabled the synthesis of an air-stable n-type PbS CQD solid. This material was used to build an air-processed inverted quantum junction device, which shows the highest current density from any CQD solar cell and a solar power conversion efficiency as high as 8%. We also feature the n-type CQD solid in the rapid, sensitive, and specific detection of atmospheric NO2. This work paves the way for new families of electronic devices that leverage air-stable quantum-tuned materials.

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Figure 1: Surface engineering of CQD solids for air stability.
Figure 2: Halide ligands incorporated in solution-phase and solid-state ligand exchanges.
Figure 3: Air-stable CQD solar cells.
Figure 4: Inverted quantum junction devices leverage process-compatible n- and p-type CQD solids.
Figure 5: Inverted quantum junction solar cell.

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Acknowledgements

This publication is based in part on work supported by Award KUS-11-009-21, made by King Abdullah University of Science and Technology (KAUST), by the Ontario Research Fund—Research Excellence Program, and by the Natural Sciences and Engineering Research Council (NSERC) of Canada. We thank Angstrom Engineering, and Innovative Technology, for useful discussions regarding material deposition methods and control of the glovebox environment, respectively. Computations were performed using the BlueGene/Q supercomputer at the SciNet HPC Consortium provided through the Southern Ontario Smart Computing Innovation Platform (SOSCIP). The SOSCIP consortium is funded by the Ontario Government and the Federal Economic Development Agency for Southern Ontario. H.D. would like to acknowledge financial support from the China Scholarship Council (CSC). The authors thank Larissa Levina for the assistance with CQDs synthesis, S. M. Thon, A. H. Ip and M. Adachi for helpful discussions, S. Masala and J. McDowell for measurement assistance, and E. Palmiano, R. Wolowiec and D. Kopilovic for their help during the course of study. We thank L. Goncharova for assistance with RBS measurements.

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Z.N., O.V., O.M.B. and E.H.S. designed and directed this study, analysed the results, and co-wrote the manuscript. Z.N. contributed to all experimental work. O.V. carried out the density functional theory simulations and XPS measurements. J.P, J.X. and H.D. assisted in device fabrication. S.H. and J.M. performed transient photovoltage experiments. V.A carried out optoelectronic simulations. M.L., H.L. and J.T. performed NO2 gas sensing measurements. K.W.K., L.R., A.L., G.C. and B.S. carried out fabrication and device characterization of specific devices. A.R.K. and A.A. performed UPS measurement. J-P.S. and I.H. carried out the Kelvin probe study.

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Correspondence to Edward H. Sargent.

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Ning, Z., Voznyy, O., Pan, J. et al. Air-stable n-type colloidal quantum dot solids. Nature Mater 13, 822–828 (2014). https://doi.org/10.1038/nmat4007

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