As the record single-junction efficiencies of perovskite solar cells now rival those of copper indium gallium selenide, cadmium telluride and multicrystalline silicon, they are becoming increasingly attractive for use in tandem solar cells due to their wide, tunable bandgap and solution processability. Previously, perovskite/silicon tandems were limited by significant parasitic absorption and poor environmental stability. Here, we improve the efficiency of monolithic, two-terminal, 1-cm2 perovskite/silicon tandems to 23.6% by combining an infrared-tuned silicon heterojunction bottom cell with the recently developed caesium formamidinium lead halide perovskite. This more-stable perovskite tolerates deposition of a tin oxide buffer layer via atomic layer deposition that prevents shunts, has negligible parasitic absorption, and allows for the sputter deposition of a transparent top electrode. Furthermore, the window layer doubles as a diffusion barrier, increasing the thermal and environmental stability to enable perovskite devices that withstand a 1,000-hour damp heat test at 85 C and 85% relative humidity.

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The authors thank M. Leilaeioun and K. Fisher for assistance with silicon cell fabrication and simulation. The information, data and work presentedherein were funded in part by the US Department of Energy (DOE) Sunshot NextGen III program under award number DE-EE0006707, the National Science Foundation (NSF) and Department of Energy under NSF Cooperative Agreement No. EEC-1041895, the Research Corporation for Science Advancement through Scialog Collaborative Innovation Award Number 23460, and the National Research Foundation Singapore through the Singapore MIT Alliance for Research and Technology’s Low Energy Electronic Systems research programme. K.A.B. is supported by the NSF Graduate Research Fellowship Program under Grant No. DGE-114747. The optical measurements were performed in part at the Stanford Nanofabrication Facility’s nSiL laboratory, which is funded by NSF award ARI-0963061. AFM and SEM were performed at the Stanford Nano Shared Facilities (SNSF). We appreciate those who provided supplies for device encapsulation: J. Kapur (Dupont) for Surlyn, L. Postak (Quanex) for Solargain edge tape, T. Orfley (Corning) for eagle glass, and S. Ebers and S. Lee (Ulbrich Solar Technologies) for bus ribbon.

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Author notes

    • Kevin A. Bush
    • , Axel F. Palmstrom
    •  & Zhengshan J. Yu

    These authors contributed equally to this work.


  1. Stanford University, Stanford 94305, USA

    • Kevin A. Bush
    • , Axel F. Palmstrom
    • , Rongrong Cheacharoen
    • , Colin D. Bailie
    • , Tomas Leijtens
    • , Maxmillian C. Minichetti
    • , Nicholas Rolston
    • , Rohit Prasanna
    • , Stacey F. Bent
    •  & Michael D. McGehee
  2. Arizona State University, Tempe 85281, USA

    • Zhengshan J. Yu
    • , Mathieu Boccard
    •  & Zachary C. Holman
  3. Massachusetts Institute of Technology, Cambridge 02139, USA

    • Jonathan P. Mailoa
    • , Robert L. Z. Hoye
    • , Ian Marius Peters
    • , Sarah Sofia
    •  & Tonio Buonassisi
  4. University of Oxford, Oxford OX1 3PU, UK

    • David P. McMeekin
    •  & Henry J. Snaith
  5. D2 Solar LLC, San Jose 95131, USA

    • Duncan Harwood
  6. Sunpreme, Sunnyvale 94085, USA

    • Wen Ma
    •  & Farhad Moghadam


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K.A.B. led the fabrication of the perovskite solar cell; A.F.P. performed the ALD process for the window layer on the perovskite solar cell; Z.J.Y. led the fabrication of the silicon heterojunction solar cell; M.B. assisted with the fabrication of the silicon nanoparticle rear reflector. R.C. packaged devices. D.P.M. initiated the perovskite development. R.L.Z.H. developed the NiOx layer. C.D.B., J.P.M., T.L. and I.M.P. aided in project ideation and planning. M.C.M. assisted in semi-transparent-perovskite fabrication. N.R. performed AFM measurements. R.P. performed transfer-matrix optical modelling. S.S. assisted in ALD work. D.H. assisted in packaging and stability testing. W.M. and F.M. assisted in ITO deposition. K.A.B., A.F.P., Z.J.Y., Z.C.H. and M.D.M. wrote the manuscript, and all the rest discussed and reviewed the manuscript. Z.C.H. and M.D.M. led the entire project.

Competing interests

The authors declare no competing financial interests.

Corresponding authors

Correspondence to Zachary C. Holman or Michael D. McGehee.

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