What is the Mechanism of MAPbI3 p-Doping by I2? Insights from Optoelectronic Properties

Arava Zohar, Igal Levine, Satyajit Gupta, Omri Davidson, Doron Azulay, Oded Millo, Isaac Balberg, Gary Hodes, David Cahen

Research output: Contribution to journalArticlepeer-review

72 Scopus citations

Abstract

Obtaining insight into, and ultimately control over, electronic doping of halide perovskites may improve tuning of their remarkable optoelectronic properties, reflected in what appear to be low defect densities and as expressed in various charge transport and optical parameters. Doping is important for charge transport because it determines the electrical field within the semiconducting photoabsorber, which strongly affects collection efficiency of photogenerated charges. Here we report on intrinsic doping of methylammonium lead tri-iodide, MAPbI3, as thin films of the types used for solar cells and LEDs, by I2 vapor at a level that does not affect the optical absorption and leads to a small (<20 meV, ∼9 nm) red shift in the photoluminescence peak. This I2 vapor treatment makes the films 10× more electronically conductive in the dark. We show that this change is due to p-type doping because we find their work function to increase by 150 mV with respect to the ionization energy (valence band maximum), which does not change upon I2 exposure. The majority carrier (hole) diffusion length increases upon doping, making the material less ambipolar. Our results are well-explained by I2 exposure decreasing the density of donor defects, likely iodide vacancies (VI) or defect complexes, containing VI. Invoking iodide interstitials, which are acceptor defects, seems less likely based on calculations of the formation energies of such defects and is in agreement with a recent report on pressed pellets.

Original languageEnglish
Pages (from-to)2408-2414
Number of pages7
JournalACS Energy Letters
Volume2
Issue number10
DOIs
StatePublished - 13 Oct 2017
Externally publishedYes

Bibliographical note

Publisher Copyright:
© 2017 American Chemical Society.

Funding

We thank Gabriel Man, L. Loo, and A. Kahn (Princeton Univ.) for the PEYS measurements, T. Bendikov (WIS) for the UPS and XPS measurements and analyses, Dan Oron (WIS) for advice and guidance to establish our TRPL system, and S. Garosi, N. Kedem, and I Schahar for advice and help with building the I2 exposure system. We are grateful to Dana and Yossie Hollander via the Weizmann Institute’s Sustainabilty and Energy Research Initiative; the Israel Ministry of Science’s Tashtiot, Israel−China, and India−Israel programs, and to the Israel National Nano-initiative for partial support and acknowledge the US−Israel Binational Science foundation for the Princeton Univ. connection; we acknowledge the historic generosity of the Harold Perlman family. D.C. holds the Sylvia and Rowland Schaefer Chair in Energy Research.

FundersFunder number
Israel National Nano-Initiative
Ministry of Science’s
Princeton University
United States-Israel Binational Science Foundation
Ministry of science and technology, Israel

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