Tandem devices combining perovskite and silicon solar cells are promising candidates to achieve power conversion efficiencies above 30% at reasonable costs. State-of-the-art monolithic two-terminal perovskite/silicon tandem devices have so far featured silicon bottom cells that are polished on their front side to be compatible with the perovskite fabrication process. This concession leads to higher potential production costs, higher reflection losses and non-ideal light trapping. To tackle this issue, we developed a top cell deposition process that achieves the conformal growth of multiple compounds with controlled optoelectronic properties directly on the micrometre-sized pyramids of textured monocrystalline silicon. Tandem devices featuring a silicon heterojunction cell and a nanocrystalline silicon recombination junction demonstrate a certified steady-state efficiency of 25.2%. Our optical design yields a current density of 19.5 mA cm2 thanks to the silicon pyramidal texture and suggests a path for the realization of 30% monolithic perovskite/silicon tandem devices.

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The authors thank F. Debrot and C. Allebé for SHJ wet-chemical processing, J. Geissbühler for help regarding the Arduino microcontroller and circuit design, G. Charitat for the bottom cell deposition and A. Walter, S.-J. Moon, T. C.-J. Yang, P. Fiala and F. Fu for help regarding perovskite top cell processes and fruitful discussions. This work was funded by the Nano-Tera.ch Synergy project, the Swiss Federal Office of Energy under grant SI/501072-01, the Swiss National Science Foundation via the Sinergia Episode (CRSII5_171000) and NRP70 Energy Turnaround PV2050 (407040) projects and the European Union’s Horizon 2020 research and innovation program under grant agreement no. 653296 (CHEOPS).

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  1. These authors contributed equally: Florent Sahli and Jérémie Werner.


  1. Ecole Polytechnique Fédérale de Lausanne (EPFL), Institute of Microengineering (IMT) Photovoltaics and Thin-Film Electronics Laboratory (PV-Lab), Neuchâtel, Switzerland

    • Florent Sahli
    • , Jérémie Werner
    • , Matthias Bräuninger
    • , Raphaël Monnard
    • , Mathieu Boccard
    • , Quentin Jeangros
    •  & Christophe Ballif
  2. CSEM, PV-Center, Neuchâtel, Switzerland

    • Brett A. Kamino
    • , Bertrand Paviet-Salomon
    • , Loris Barraud
    • , Laura Ding
    • , Juan J. Diaz Leon
    • , Davide Sacchetto
    • , Gianluca Cattaneo
    • , Matthieu Despeisse
    • , Sylvain Nicolay
    • , Bjoern Niesen
    •  & Christophe Ballif


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F.S. and J.W. contributed equally to this work. F.S and J.W designed the experiments and carried out the device fabrication. B.A.K. and M.Br. contributed to the development of the perovskite top cell. R.M., B.P.-S., L.B., M.Bo. and M.D. developed and fabricated the silicon heterojunction bottom cells. D.S., L.D. and J.J.D.L developed the ALD buffer layer. G.C. and B.N. carried out the encapsulation for stability tests. Q.J. performed the FIB and TEM characterization and, with J.W., the SEM analysis. M.Br. recorded the AFM data. F.S., J.W. and Q.J. carried out data analysis and prepared the figures. J.W. carried out the degradation stability tests and analysed the data. Q.J., B.N., M.Bo., M.D., S.N. and C.B. supervised different parts of the work. F.S. and Q.J. wrote the paper, and all authors commented on the manuscript.

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Correspondence to Florent Sahli or Quentin Jeangros.

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