Hybrid organic–inorganic inks flatten the energy landscape in colloidal quantum dot solids

Abstract

Bandtail states in disordered semiconductor materials result in losses in open-circuit voltage (Voc) and inhibit carrier transport in photovoltaics. For colloidal quantum dot (CQD) films that promise low-cost, large-area, air-stable photovoltaics, bandtails are determined by CQD synthetic polydispersity and inhomogeneous aggregation during the ligand-exchange process. Here we introduce a new method for the synthesis of solution-phase ligand-exchanged CQD inks that enable a flat energy landscape and an advantageously high packing density. In the solid state, these materials exhibit a sharper bandtail and reduced energy funnelling compared with the previous best CQD thin films for photovoltaics. Consequently, we demonstrate solar cells with higher Voc and more efficient charge injection into the electron acceptor, allowing the use of a closer-to-optimum bandgap to absorb more light. These enable the fabrication of CQD solar cells made via a solution-phase ligand exchange, with a certified power conversion efficiency of 11.28%. The devices are stable when stored in air, unencapsulated, for over 1,000 h.

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Figure 1: Solution-phase ligand exchange with metal halide precursors and ammonium acetate.
Figure 2: PbS CQDs exchanged by lead halide with the aid of ammonium acetate suggest improved CQD packing density and sharper bandtail.
Figure 3: Energy funnelling in the exchanged CQD films.
Figure 4: The effect of flat energy landscape on CQD solar cell performance.
Figure 5: Certified solar cell performance.

References

  1. 1

    McDonald, S. A. et al. Solution-processed PbS quantum dot infrared photodetectors and photovoltaics. Nat. Mater. 4, 138–142 (2005).

    CAS  Google Scholar 

  2. 2

    Kamat, P. V. Quantum dot solar cells. Semiconductor nanocrystals as light harvesters. J. Phys. Chem. C 112, 18737–18753 (2008).

    CAS  Google Scholar 

  3. 3

    Luther, J. M. et al. Schottky solar cells based on colloidal nanocrystal films. Nano Lett. 8, 3488–3492 (2008).

    CAS  Google Scholar 

  4. 4

    Nozik, A. J. et al. Semiconductor quantum dots and quantum dot arrays and applications of multiple exciton generation to third-generation photovoltaic solar cells. Chem. Rev. 110, 6873–6890 (2010).

    CAS  Google Scholar 

  5. 5

    Konstantatos, G. et al. Ultrasensitive solution-cast quantum dot photodetectors. Nature 442, 180–183 (2006).

    CAS  Google Scholar 

  6. 6

    Lee, J.-S., Kovalenko, M. V., Huang, J., Chung, D. S. & Talapin, D. V. Band-like transport, high electron mobility and high photoconductivity in all-inorganic nanocrystal arrays. Nat. Nanotech. 6, 348–352 (2011).

    CAS  Google Scholar 

  7. 7

    Sun, Q. J. et al. Bright, multicoloured light-emitting diodes based on quantum dots. Nat. Photon. 1, 717–722 (2007).

    CAS  Google Scholar 

  8. 8

    Hoogland, S. et al. A solution-processed 1.53 μm quantum dot laser with temperature-invariant emission wavelength. Opt. Express 14, 3273–3281 (2006).

    CAS  Google Scholar 

  9. 9

    Chuang, C.-H. M., Brown, P. R., Bulović, V. & Bawendi, M. G. Improved performance and stability in quantum dot solar cells through band alignment engineering. Nat. Mater. 13, 796–801 (2014).

    CAS  Google Scholar 

  10. 10

    Lan, X. et al. Passivation using molecular halides increases quantum dot solar cell performance. Adv. Mater. 28, 299–304 (2016).

    CAS  Google Scholar 

  11. 11

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

    CAS  Google Scholar 

  12. 12

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

    CAS  Google Scholar 

  13. 13

    Ning, Z. et al. All-inorganic colloidal quantum dot photovoltaics employing solution-phase halide passivation. Adv. Mater. 24, 6295–6299 (2012).

    CAS  Google Scholar 

  14. 14

    Ning, Z. et al. Air-stable n-type colloidal quantum dot solids. Nat. Mater. 13, 822–828 (2014).

    CAS  Google Scholar 

  15. 15

    Lan, X. et al. 10.6% certified colloidal quantum dot solar cells via solvent-polarity-engineered halide passivation. Nano Lett. 16, 4630–4634 (2016).

    CAS  Google Scholar 

  16. 16

    Ip, A. H. et al. Infrared colloidal quantum dot photovoltaics via coupling enhancement and agglomeration suppression. ACS Nano 9, 8833–8842 (2015).

    CAS  Google Scholar 

  17. 17

    Carey, G. H., Levina, L., Comin, R., Voznyy, O. & Sargent, E. H. Record charge carrier diffusion length in colloidal quantum dot solids via mutual dot-to-dot surface passivation. Adv. Mater. 27, 3325–3330 (2015).

    CAS  Google Scholar 

  18. 18

    Yang, Z. et al. Colloidal quantum dot photovoltaics enhanced by perovskite shelling. Nano Lett. 15, 7539–7543 (2015).

    CAS  Google Scholar 

  19. 19

    Pejova, B. & Abay, B. Nanostructured CdSe films in low size-quantization regime: temperature dependence of the band gap energy and sub-band gap absorption tails. J. Phys. Chem. C 115, 23241–23255 (2011).

    CAS  Google Scholar 

  20. 20

    Pejova, B., Abay, B. & Bineva, I. Temperature dependence of the band-gap energy and sub-band-gap absorption tails in strongly quantized ZnSe nanocrystals deposited as thin films. J. Phys. Chem. C 114, 15280–15291 (2010).

    CAS  Google Scholar 

  21. 21

    Zhitomirsky, D. et al. Colloidal quantum dot photovoltaics: the effect of polydispersity. Nano Lett. 12, 1007–1012 (2012).

    CAS  Google Scholar 

  22. 22

    Guyot-Sionnest, P. Electrical transport in colloidal quantum dot films. J. Phys. Chem. Lett. 3, 1169–1175 (2012).

    CAS  Google Scholar 

  23. 23

    Sa-Yakanit, V. & Glyde, H. R. Urbach tails and disorder. Comments Condens. Matter Phys. 13, 35–48 (1987).

    CAS  Google Scholar 

  24. 24

    Erslev, P. T. et al. Sharp exponential band tails in highly disordered lead sulfide quantum dot arrays. Phys. Rev. B. 86, 155313–155316 (2012).

    Google Scholar 

  25. 25

    Kagan, C. R. & Murray, C. B. Charge transport in strongly coupled quantum dot solids. Nat. Nanotech. 10, 1013–1026 (2015).

    CAS  Google Scholar 

  26. 26

    Hess, K., Leburton, J. P. & Ravaioli, U. Hot Carriers in Semiconductors Ch. 3 (Plenum Press, 1996).

    Google Scholar 

  27. 27

    Gao, Y. et al. Enhanced hot-carrier cooling and ultrafast spectral diffusion in strongly coupled PbSe quantum-dot solids. Nano Lett. 11, 5471–5476 (2011).

    CAS  Google Scholar 

  28. 28

    Chuang, C.-H. M. et al. Open-circuit voltage deficit, radiative sub-bandgap states, and prospects in quantum dot solar cells. Nano Lett. 15, 3286–3294 (2015).

    CAS  Google Scholar 

  29. 29

    Gao, J. & Johnson, J. C. Charge trapping in bright and dark states of coupled PbS quantum dot films. ACS Nano 6, 3292–3303 (2012).

    CAS  Google Scholar 

  30. 30

    Weidman, M. C., Beck, M. E., Hoffman, R. S., Prins, F. & Tisdale, W. A. Monodisperse, air-stable PbS nanocrystals via precursor stoichiometry control. ACS Nano 8, 6363–6371 (2014).

    CAS  Google Scholar 

  31. 31

    Zhang, H., Jang, J., Liu, W. & Talapin, D. V. Colloidal nanocrystals with inorganic halide, pseudohalide, and halometallate ligands. ACS Nano 8, 7359–7369 (2014).

    CAS  Google Scholar 

  32. 32

    Nag, A., Zhang, H., Janke, E. & Talapin, D. V. Inorganic surface ligands for colloidal nanomaterials. Z. Phys. Chem. 229, 85–107 (2015).

    CAS  Google Scholar 

  33. 33

    Dirin, D. N. et al. Lead halide perovskites and other metal halide complexes as inorganic capping ligands for colloidal nanocrystals. J. Am. Chem. Soc. 136, 6550–6553 (2014).

    CAS  Google Scholar 

  34. 34

    Ning, Z., Dong, H., Zhang, Q., Voznyy, O. & Sargent, E. H. Solar cells based on inks of n-type colloidal quantum dots. ACS Nano 8, 10321–10327 (2014).

    CAS  Google Scholar 

  35. 35

    Balazs, D. M. et al. Counterion-mediated ligand exchange for PbS colloidal quantum dot superlattices. ACS Nano 9, 11951–11959 (2015).

    CAS  Google Scholar 

  36. 36

    Tang, J. et al. Quantum dot photovoltaics in the extreme quantum confinement regime: the surface-chemical origins of exceptional air-and light-stability. ACS Nano 4, 869–878 (2010).

    CAS  Google Scholar 

  37. 37

    Bian, K. et al. Shape-anisotropy driven symmetry transformations in nanocrystal superlattice polymorphs. ACS Nano 5, 2815–2823 (2011).

    CAS  Google Scholar 

  38. 38

    John, S. Theory of electron band tails and Urbach optical-absorption edge. Pyhs. Rev. Lett. 57, 1777–1780 (1986).

    CAS  Google Scholar 

  39. 39

    Peterson, J. J. & Krauss, T. D. Fluorescence spectroscopy of single lead sulfide quantum dots. Nano Lett. 6, 510–514 (2006).

    CAS  Google Scholar 

  40. 40

    Venkateshvaran, D. et al. Approaching disorder-free transport in high-mobility conjugated polymers. Nature 515, 384–388 (2014).

    CAS  Google Scholar 

  41. 41

    Moreels, I. et al. Size-dependent optical properties of colloidal PbS quantum dots. ACS Nano 3, 3023–3030 (2009).

    CAS  Google Scholar 

  42. 42

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

    CAS  Google Scholar 

  43. 43

    Zhitomirsky, D., Voznyy, O., Hoogland, S. & Sargent, E. H. Measuring charge carrier diffusion in coupled colloidal quantum dot solids. ACS Nano 7, 5282–5290 (2013).

    CAS  Google Scholar 

  44. 44

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

    CAS  Google Scholar 

  45. 45

    Kunneman, L. T. et al. Nature and decay pathways of photoexcited states in CdSe and CdSe/CdS nanoplatelets. Nano Lett. 14, 7039–7045 (2014).

    CAS  Google Scholar 

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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. F.P.G.d.A. acknowledges financial support from the Connaught fund. A.H.B. and F.L. thank K. Vandewal for his contribution to the photothermal deflection spectroscopy set-up and M. Baier for help with the experiments. The authors thank E. Palmiano, L. Levina, R. Wolowiec, D. Kopilovic, G. Kim and F. Fan for their help during the course of study.

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M.L. conceived the idea and contributed to most experimental work. O.V., S.H. and E.H.S. supervised the project. O.V. carried out XPS measurements. R.S. performed transient absorption spectroscopy measurements. F.P.G.d.A. assisted in EQE measurements. R.M., A.R.K. and A.A. performed GISAXS measurements. A.H.B. and F.L. performed photothermal deflection spectroscopy measurements. X.L. assisted in device fabrication. F.F. performed TEM measurements. G.W. carried out PL studies. M.L., O.V. and E.H.S. wrote the manuscript. All the authors provided comments on the text.

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Correspondence to Edward H. Sargent.

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Liu, M., Voznyy, O., Sabatini, R. et al. Hybrid organic–inorganic inks flatten the energy landscape in colloidal quantum dot solids. Nature Mater 16, 258–263 (2017). https://doi.org/10.1038/nmat4800

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