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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McDonald, S. A. et al. Solution-processed PbS quantum dot infrared photodetectors and photovoltaics. Nat. Mater. 4, 138–142 (2005).
Kamat, P. V. Quantum dot solar cells. Semiconductor nanocrystals as light harvesters. J. Phys. Chem. C 112, 18737–18753 (2008).
Luther, J. M. et al. Schottky solar cells based on colloidal nanocrystal films. Nano Lett. 8, 3488–3492 (2008).
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).
Konstantatos, G. et al. Ultrasensitive solution-cast quantum dot photodetectors. Nature 442, 180–183 (2006).
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).
Sun, Q. J. et al. Bright, multicoloured light-emitting diodes based on quantum dots. Nat. Photon. 1, 717–722 (2007).
Hoogland, S. et al. A solution-processed 1.53 μm quantum dot laser with temperature-invariant emission wavelength. Opt. Express 14, 3273–3281 (2006).
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).
Lan, X. et al. Passivation using molecular halides increases quantum dot solar cell performance. Adv. Mater. 28, 299–304 (2016).
Ip, A. H. et al. Hybrid passivated colloidal quantum dot solids. Nat. Nanotech. 7, 577–582 (2012).
Tang, J. et al. Colloidal-quantum-dot photovoltaics using atomic-ligand passivation. Nat. Mater. 10, 765–771 (2011).
Ning, Z. et al. All-inorganic colloidal quantum dot photovoltaics employing solution-phase halide passivation. Adv. Mater. 24, 6295–6299 (2012).
Ning, Z. et al. Air-stable n-type colloidal quantum dot solids. Nat. Mater. 13, 822–828 (2014).
Lan, X. et al. 10.6% certified colloidal quantum dot solar cells via solvent-polarity-engineered halide passivation. Nano Lett. 16, 4630–4634 (2016).
Ip, A. H. et al. Infrared colloidal quantum dot photovoltaics via coupling enhancement and agglomeration suppression. ACS Nano 9, 8833–8842 (2015).
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).
Yang, Z. et al. Colloidal quantum dot photovoltaics enhanced by perovskite shelling. Nano Lett. 15, 7539–7543 (2015).
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).
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).
Zhitomirsky, D. et al. Colloidal quantum dot photovoltaics: the effect of polydispersity. Nano Lett. 12, 1007–1012 (2012).
Guyot-Sionnest, P. Electrical transport in colloidal quantum dot films. J. Phys. Chem. Lett. 3, 1169–1175 (2012).
Sa-Yakanit, V. & Glyde, H. R. Urbach tails and disorder. Comments Condens. Matter Phys. 13, 35–48 (1987).
Erslev, P. T. et al. Sharp exponential band tails in highly disordered lead sulfide quantum dot arrays. Phys. Rev. B. 86, 155313–155316 (2012).
Kagan, C. R. & Murray, C. B. Charge transport in strongly coupled quantum dot solids. Nat. Nanotech. 10, 1013–1026 (2015).
Hess, K., Leburton, J. P. & Ravaioli, U. Hot Carriers in Semiconductors Ch. 3 (Plenum Press, 1996).
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).
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).
Gao, J. & Johnson, J. C. Charge trapping in bright and dark states of coupled PbS quantum dot films. ACS Nano 6, 3292–3303 (2012).
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).
Zhang, H., Jang, J., Liu, W. & Talapin, D. V. Colloidal nanocrystals with inorganic halide, pseudohalide, and halometallate ligands. ACS Nano 8, 7359–7369 (2014).
Nag, A., Zhang, H., Janke, E. & Talapin, D. V. Inorganic surface ligands for colloidal nanomaterials. Z. Phys. Chem. 229, 85–107 (2015).
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).
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).
Balazs, D. M. et al. Counterion-mediated ligand exchange for PbS colloidal quantum dot superlattices. ACS Nano 9, 11951–11959 (2015).
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).
Bian, K. et al. Shape-anisotropy driven symmetry transformations in nanocrystal superlattice polymorphs. ACS Nano 5, 2815–2823 (2011).
John, S. Theory of electron band tails and Urbach optical-absorption edge. Pyhs. Rev. Lett. 57, 1777–1780 (1986).
Peterson, J. J. & Krauss, T. D. Fluorescence spectroscopy of single lead sulfide quantum dots. Nano Lett. 6, 510–514 (2006).
Venkateshvaran, D. et al. Approaching disorder-free transport in high-mobility conjugated polymers. Nature 515, 384–388 (2014).
Moreels, I. et al. Size-dependent optical properties of colloidal PbS quantum dots. ACS Nano 3, 3023–3030 (2009).
Pattantyus-Abraham, A. G. et al. Depleted-heterojunction colloidal quantum dot solar cells. ACS Nano 4, 3374–3380 (2010).
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).
Ning, Z. et al. Graded doping for enhanced colloidal quantum dot photovoltaics. Adv. Mater. 25, 1719–1723 (2013).
Kunneman, L. T. et al. Nature and decay pathways of photoexcited states in CdSe and CdSe/CdS nanoplatelets. Nano Lett. 14, 7039–7045 (2014).
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.
The authors declare no competing financial interests.
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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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