CaltechAUTHORS
Published September 17, 2025 | Version Supplemental material
Journal Article Open

A chemically bonded monolayer interface enables enhanced thermal stability and efficiency in Pb-Sn perovskite solar cells

Creators

  • 1. ROR icon Northwestern University
  • 2. ROR icon California Institute of Technology
  • 3. ROR icon University of Toronto
  • 4. ROR icon University of Queensland
  • 5. ROR icon ALBA Synchrotron (Spain)
  • 6. ROR icon Linköping University
  • 7. ROR icon École Polytechnique Fédérale de Lausanne
  • 8. ROR icon University of Ioannina
  • 9. ROR icon Arizona State University
  • 10. ROR icon King Abdullah University of Science and Technology

Abstract

Advances in narrow-band-gap (NBG) mixed lead-tin (Pb-Sn) perovskites have enabled increasingly efficient all-perovskite tandem solar cells, yet device stability remains limited by acidic poly(3,4-ethylenedioxythiophene) polystyrenesulfonate (PEDOT:PSS) hole transport materials (HTMs). Although carbazole-based self-assembled monolayers (SAMs) were considered as alternatives, they also degrade rapidly (T80 < 200 h) under external stresses. We identified weak chemical interaction at the transparent conductive oxide:SAM:perovskite interface and hypothesized that stronger binding could enhance stability. Introducing bifunctional SAMs with thiol groups established robust S-Pb chemical coordination, improving fracture energy by 30%. Replacing acidic phosphonic groups with milder carboxylic groups and optimizing SAM chain length led to selecting 16-mercaptohexadecanoic acid (16-MHDA), balancing coverage, energy alignment, and series resistance. This approach doubled photocarrier lifetime and increased thermal degradation resistance by 1.3×. Single-junction Pb-Sn cells achieved 24% power conversion efficiency (PCE) and encapsulated devices retained 80% efficiency after 680 h under 1-sun illumination at a heatsink temperature of 50°C.

Copyright and License

© 2025 Elsevier Inc. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

Acknowledgement

This work was supported by the Trienens Institute for Sustainability and Energy at Northwestern University. This work is partially supported by award 70NANB19H005 from US Department of Commerce, National Institute of Standards and Technology as part of the Center for Hierarchical Materials Design (CHiMaD). This work made use of the NUFAB facility of Northwestern University’s NUANCE Center, which has received support from the SHyNE Resource (NSF ECCS-2025633), the IIN, and Northwestern’s MRSEC program (NSF DMR-2308691). A.S.R.B. acknowledges support from King Abdullah University of Science and Technology (KAUST) through the Ibn Rushd Postdoctoral Fellowship Award. Part of the research described in this paper was performed at the CLS, a national research facility of the University of Saskatchewan, which is supported by the Canada Foundation for Innovation (CFI), the Natural Sciences and Engineering Research Council (NSERC), the National Research Council (NRC), the Canadian Institutes of Health Research (CIHR), the Government of Saskatchewan, and the University of Saskatchewan. DFT calculations were conducted in the Resnick High Performance Computing Center, a facility supported by Resnick Sustainability Institute at the California Institute of Technology. DFT calculations were also supported through computational resources and staff contributions provided for the Quest high-performance computing facility at Northwestern University which is jointly supported by the Office of the Provost, the Office of Research, and Northwestern University Information Technology. J.A.S. acknowledges financial support from the Australian Research Council (DE230100173). The in situ GIWAXS data were collected at NCD-SWEET beamline at ALBA synchrotron (Spain) with the collaboration of ALBA staff. C.B.M. and W.A.G. acknowledge support from the Liquid Sunlight Alliance, which is supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, Fuels from Sunlight Hub under award number DE-SC0021266. U.R. acknowledges funding from the SNSF under grant no. 200020_219440 and computational resources from the Swiss National Computing Center CSCS. N.R. acknowledges support from the National Science Foundation under grant no. 2339233. The authors thank Selina Olthof for useful discussions.

Contributions

A.S.R.B. conceived the idea and designed the project. A.S.R.B. fabricated, tested, and characterized the solar cells. C.L. assisted with device characterization. I.W.G. assisted with energy level measurements. A.M. carried out PLQY and TRPL measurements. J.A.S., E.S., R.Z., and L.W. performed GIWAXS measurements and analysis. Y.Y., H.C., and D.C. assisted with performing and analysis of XRD and PL. H.W. and L.Z. helped with contact angle measurements and film fabrication. J.X., C.B.M., and W.A.G. conducted the DFT calculations. C.H. performed KPFM measurements. B.R. and A.M. conducted the TA measurements. L.G. carried out the GISAXS measurements and corresponding data analysis. A.S.R.B. wrote the first draft of the manuscript. N.L., V.C., V.S., and A.V. performed the MD simulations and analysis under the supervision of U.R. C.L. offered feedback on the structure of the manuscript. C.L. and A.M. helped with writing – review and editing. M.G.K. assisted with revising the manuscript. B.C., O.M.B., and E.H.S. supervised the work. All authors discussed and commented on the manuscript.

Conflict of Interest

A.S.R.B., B.C., and E.H.S. are filing a patent based on this work.

Supplemental Material

Document S1. Figures S1–S26, Tables S1–S4, and supplemental notes

Data S1. Standardized data reporting for photovoltaic cells

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1-s2.0-S2542435125002284-mmc1.pdf

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Additional details

Funding

Northwestern University
United States Department of Commerce
70NANB19H005
National Institute of Standards and Technology
Center for Hierarchical Materials Design
National Science Foundation
ECCS-2025633
National Science Foundation
DMR-2308691
King Abdullah University of Science and Technology
University of Saskatchewan
Canada Foundation for Innovation
Natural Sciences and Engineering Research Council
National Research Council Canada
Canadian Institutes of Health Research
Government of Saskatchewan
Resnick Sustainability Institute
Australian Research Council
DE230100173
United States Department of Energy
DE-SC0021266
Swiss National Science Foundation
200020_219440
National Science Foundation
2339233

Dates

Submitted
2025-02-06
Accepted
2025-06-23
Available
2025-07-15
Available online
Available
2025-09-17
Version of record

Caltech Custom Metadata

Caltech groups
Division of Chemistry and Chemical Engineering (CCE) , Liquid Sunlight Alliance , Materials and Process Simulation Center , Resnick Sustainability Institute
Publication Status
Published