Influence of Surface Ligands on Energetics at FASnI3/C60 Interfaces and Their Impact on Photovoltaic Performance

Alex M. Boehm, Tuo Liu, So Min Park, Ashkan Abtahi, Kenneth R. Graham

Research output: Contribution to journalArticlepeer-review

28 Scopus citations


Interfacial chemistry and energetics significantly impact the performance of photovoltaic devices. In the case of Pb-containing organic metal halide perovskites, photoelectron spectroscopy has been used to determine the energetic alignment of frontier electronic energy levels at various interfaces present in the photovoltaic device. For the Sn-containing analogues, which are less toxic, no such measurements have been made. Through a combination of ultraviolet, inverse, and X-ray photoelectron spectroscopy (UPS, IPES, and XPS, respectively) measurements taken at varying thickness increments during stepwise deposition of C60 on FASnI3, we present the first direct measurements of the frontier electronic energy levels across the FASnI3/C60 interface. The results show band bending in both materials and transport gap widening in FASnI3 at the interface with C60. The XPS results show that iodide diffuses into C60 and results in n-doping of C60. This iodide diffusion out of FASnI3 impacts the valence and conduction band energies of FASnI3 more than the core levels, with the core level shifts displaying a different trend than the valence and conduction bands. Surface treatment of FASnI3 with carboxylic acids and bulky ammonium substituted surface ligands results in slight alterations in the interfacial energetics, and all surface ligands result in similar or improved PV performance relative to the untreated devices. The greatest PV stability results from treatment with a fluorinated carboxylic acid derivative; however, iodide diffusion is still observed to occur with this surface ligand.

Original languageEnglish
Pages (from-to)5209-5218
Number of pages10
JournalACS Applied Materials and Interfaces
Issue number5
StatePublished - Feb 5 2020

Bibliographical note

Funding Information:
We gratefully acknowledge the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, and the EPSCoR program, under Award No. DE-SC0018208.

Publisher Copyright:
Copyright © 2019 American Chemical Society.


  • formamidinium tin iodide
  • interfacial energetics
  • inverse photoelectron spectroscopy
  • ion diffusion
  • perovskite solar cell
  • photoelectron spectroscopy
  • surface modification

ASJC Scopus subject areas

  • Materials Science (all)


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