Understanding and controlling the energy level alignment at interfaces with metal halide perovskites (MHPs) is essential for realizing the full potential of these materials for use in optoelectronic devices. To date, however, the basic electronic properties of MHPs are still under debate. Particularly, reported Fermi level positions in the energy gap vary from indicating strong n- to strong p-type character for nominally identical materials, raising serious questions about intrinsic and extrinsic defects as dopants. In this work, photoemission experiments demonstrate that thin films of the prototypical methylammonium lead triiodide (MAPbI3) behave like an intrinsic semiconductor in the absence of oxygen. Oxygen is then shown to be able to reversibly diffuse into and out of the MAPbI3 bulk, requiring rather long saturation timescales of ≈1 h (in: ambient air) and over 10 h (out: ultrahigh vacuum), for few 100 nm thick films. Oxygen in the bulk leads to pronounced p-doping, positioning the Fermi level universally ≈0.55 eV above the valence band maximum. The key doping mechanism is suggested to be molecular oxygen substitution of iodine vacancies, supported by density functional theory calculations. This insight rationalizes previous and future electronic property studies of MHPs and calls for meticulous oxygen exposure protocols.
|Publication status||Published - 2021 Jun 10|
Bibliographical noteFunding Information:
This work was funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation, Project numbers: 182087777‐SFB951 and 423749265‐SPP2196 “SURPRISE”). Work at the Weizmann Institute was supported by the Minerva Center for Self‐Healing Materials. L.K. holds the Aryeh and Mintzi Katzman Professorial Chair.
This work was funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation, Project numbers: 182087777-SFB951 and 423749265-SPP2196 ?SURPRISE?). Work at the Weizmann Institute was supported by the Minerva Center for Self-Healing Materials. L.K. holds the Aryeh and Mintzi Katzman Professorial Chair. Open access funding enabled and organized by Projekt DEAL.
© 2021 The Authors. Advanced Materials published by Wiley-VCH GmbH
All Science Journal Classification (ASJC) codes
- Materials Science(all)
- Mechanics of Materials
- Mechanical Engineering