Overcoming Redox Reactions at Perovskite-Nickel Oxide Interfaces to Boost Voltages in Perovskite Solar Cells

Caleb C. Boyd, R. Clayton Shallcross, Taylor Moot, Ross Kerner, Luca Bertoluzzi, Arthur Onno, Shalinee Kavadiya, Cullen Chosy, Eli J. Wolf, Jérémie Werner, James A. Raiford, Camila de Paula, Axel F. Palmstrom, Zhengshan J. Yu, Joseph J. Berry, Stacey F. Bent, Zachary C. Holman, Joseph M. Luther, Erin L. Ratcliff, Neal R. ArmstrongMichael D. McGehee

Research output: Contribution to journalArticlepeer-review

101 Scopus citations


Nickel oxide (NiOx) hole transport layers (HTLs) are desirable contacts for perovskite photovoltaics because they are low cost, stable, and readily scalable; however, they deliver lower open-circuit voltages (VOCs) compared to organic HTLs. Here, we characterize and mitigate electron transfer-proton transfer reactions between NiOx HTLs and perovskite precursors. Using XPS and UPS characterization, we identify that Ni≥3+ metal cation sites in NiOx thin films act both as Brønsted proton acceptors and Lewis electron acceptors, deprotonating cationic amines and oxidizing iodide species, forming PbI2−xBrx-rich hole extraction barriers at the perovskite-NiOx interface. Titrating reactive Ni≥3+ surface states with excess A-site cation salts during perovskite active layer deposition yielded an increase in VOC values to 1.15 V and power conversion efficiencies of ∼20%. This may be a general finding for metal oxide contacts that act as Brønsted and Lewis acid-base reactants toward perovskite precursors, an observation that has also been made recently for TiO2 and SnO2 contacts.

Original languageEnglish (US)
Pages (from-to)1759-1775
Number of pages17
Issue number8
StatePublished - Aug 19 2020


  • chemical reaction
  • nickel oxide
  • open-circuit voltage
  • oxidation
  • oxide
  • perovskite solar cell
  • reduction
  • stability
  • ultraviolet photoelectron spectroscopy
  • x-ray photoelectron spectroscopy

ASJC Scopus subject areas

  • Energy(all)


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