Letter | Published:

2D matrix engineering for homogeneous quantum dot coupling in photovoltaic solids

Abstract

Colloidal quantum dots (CQDs) are promising photovoltaic (PV) materials because of their widely tunable absorption spectrum controlled by nanocrystal size1,2. Their bandgap tunability allows not only the optimization of single-junction cells, but also the fabrication of multijunction cells that complement perovskites and silicon3. Advances in surface passivation2,4,5,6,7, combined with advances in device structures8, have contributed to certified power conversion efficiencies (PCEs) that rose to 11% in 20169. Further gains in performance are available if the thickness of the devices can be increased to maximize the light harvesting at a high fill factor (FF). However, at present the active layer thickness is limited to ~300 nm by the concomitant photocarrier diffusion length. To date, CQD devices thicker than this typically exhibit decreases in short-circuit current (JSC) and open-circuit voltage (VOC), as seen in previous reports3,9,10,11. Here, we report a matrix engineering strategy for CQD solids that significantly enhances the photocarrier diffusion length. We find that a hybrid inorganic–amine coordinating complex enables us to generate a high-quality two-dimensionally (2D) confined inorganic matrix that programmes internanoparticle spacing at the atomic scale. This strategy enables the reduction of structural and energetic disorder in the solid and concurrent improvements in the CQD packing density and uniformity. Consequently, planar devices with a nearly doubled active layer thicknesses (~600 nm) and record values of JSC (32 mA cm−2) are fabricated. The VOC improved as the current was increased. We demonstrate CQD solar cells with a certified record efficiency of 12%.

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Acknowledgements

This publication is based in part on work supported by the Natural Sciences and Engineering Research Council of Canada, by the Ontario Research Fund Research Excellence Program and by Award OSR-2017-CPF-3321-03 made by King Abdullah University of Science and Technology (KAUST). Some of the GIWAXS/GISAXS measurements were performed at the Cornell High Energy Synchrotron Source (CHESS), supported by the NSF Award DMR-1332208. This work also made use of the South Carolina SAXS Collaborative using a SAXSLab Ganesha for the GISAXS/GIWAXS measurements, supported by the NSF Major Research Instrumentation program (award no. DMR-1428620). We thank U. Jeng for the GIWAXS tested at the National Synchrotron Radiation Research Center, Taiwan, China. We thank L. Goncharova for assistance with RBS measurements. We thank D. Kopilovic, E. Palmiano, L. Levina and R. Wolowiec for the technical support.

Author information

J.X. conceived the idea and contributed to most experimental work. E.H.S. supervised the project. O.V., A.A. and S.O.K. co-supervised the project. Mengxia Liu assisted in the device fabrication and experiment design. S.H. assisted in the devices certificate and experiment design. A.R.K., M.A. and A.A. performed the in situ measurements of film formation. R.M., M.S., A.S. and R.Q.B. carried out the GISAXS/WAXS measurements. G.W. and M.W. performed the AFM and PL measurements. A.H.P. performed the TA measurements. B.S. carried out the FET measurements. O.V. and O.O. carried out the device simulations. Min Liu carried out microscopic studies. O.V. facilitated the RBS analysis. J.X., O.V. and E.H.S. wrote the manuscript. All the authors assisted in the experiments and provided comments on the text.

Competing interests

The authors declare no competing interests.

Correspondence to Aram Amassian or Edward H. Sargent.

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Further reading

  • Lattice anchoring stabilizes solution-processed semiconductors

    • Mengxia Liu
    • , Yuelang Chen
    • , Chih-Shan Tan
    • , Rafael Quintero-Bermudez
    • , Andrew H. Proppe
    • , Rahim Munir
    • , Hairen Tan
    • , Oleksandr Voznyy
    • , Benjamin Scheffel
    • , Grant Walters
    • , Andrew Pak Tao Kam
    • , Bin Sun
    • , Min-Jae Choi
    • , Sjoerd Hoogland
    • , Aram Amassian
    • , Shana O. Kelley
    • , F. Pelayo García de Arquer
    •  & Edward H. Sargent

    Nature (2019)

Fig. 1: Engineering the microscopic nature of the matrix to increase the ordering and photocarrier diffusion length in CQD solids for solar cells.
Fig. 2: Enhanced 2D confinement in the matrix of CQD solids.
Fig. 3: Enhanced packing density and uniformity, and reduced structural disorder in CQD solids for solar cells.
Fig. 4: Reduced energetic disorder and enhanced electronic transport in CQD solids.
Fig. 5: Enhanced solar cell performance in thick CQD absorbers that result from increased photocarrier diffusion lengths.