Colloidal-quantum-dot photovoltaics using atomic-ligand passivation

Abstract

Colloidal-quantum-dot (CQD) optoelectronics offer a compelling combination of solution processing and spectral tunability through quantum size effects. So far, CQD solar cells have relied on the use of organic ligands to passivate the surface of the semiconductor nanoparticles. Although inorganic metal chalcogenide ligands have led to record electronic transport parameters in CQD films, no photovoltaic device has been reported based on such compounds. Here we establish an atomic ligand strategy that makes use of monovalent halide anions to enhance electronic transport and successfully passivate surface defects in PbS CQD films. Both time-resolved infrared spectroscopy and transient device characterization indicate that the scheme leads to a shallower trap state distribution than the best organic ligands. Solar cells fabricated following this strategy show up to 6% solar AM1.5G power-conversion efficiency. The CQD films are deposited at room temperature and under ambient atmosphere, rendering the process amenable to low-cost, roll-by-roll fabrication.

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Figure 1: Organic and atomic passivation strategies.
Figure 2: Materials characterization following halide anion treatment.
Figure 3: Photovoltaic device physics and performance.
Figure 4: TRIR characterization of Br-capped PbS CQD film.
Figure 5: Light-intensity-dependent photovoltaic performance and frequency dependent photodiode performance.

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Acknowledgements

This publication is based in part on work supported by Award No. KUS–11–009-21, made by King Abdullah University of Science and Technology (KAUST). We thank Angstrom Engineering and Innovative Technologies for useful discussions concerning material deposition methods and control of the glovebox environment, respectively. The authors thank H. Zhong, R. Li, L. Brzozowski, V. Sukhovatkin, A. Barkhouse, I. Kramer, G. Koleilat, E. Palmiano and R. Wolowiec for their help during the course of study. R.D. acknowledges the financial support of e8 scholarship. K.S.J. and J.B.A. gratefully acknowledge partial support from the Petroleum Research Fund (PRF #49639-ND6), the National Science Foundation (CHE 0846241), and the Office of Naval Research (N00014-11-1-0239).

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J.T. and E.H.S. designed and directed this study and analysed the experimental results. J.T. contributed to all the experimental work. K.W.K. and S.H. carried out the photodiode work and K.W.K. assisted in all the experimental work. K.S.J. and J.B.A. carried out the TRIR experiments and analysed the data. H.L. fabricated the TiO2 electrodes. L.L. synthesized the PbS CQDs. K.W.K., L.L. and R.D. contributed to the solution Cd treatment experiment. D.C, K.W.C. and A.A. carried out the GISAXS and TEM measurements and analysed the data. S.H., M.F., X.W., H.L., A.F. and R.D. assisted in device fabrication and characterization. J.T., J.B.A. and E.H.S. wrote the manuscript. All authors commented on the paper.

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Correspondence to Edward H. Sargent.

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Tang, J., Kemp, K., Hoogland, S. et al. Colloidal-quantum-dot photovoltaics using atomic-ligand passivation. Nature Mater 10, 765–771 (2011). https://doi.org/10.1038/nmat3118

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