Electrochemical Doping of Halide Perovskites by Noble Metal Interstitial Cations

Abstract

Metal halide perovskites are an attractive class of semiconductors, but it has proven difficult to control their electronic doping by conventional strategies due to screening and compensation by mobile ions or ionic defects. Noble-metal interstitials represent an under-studied class of extrinsic defects that plausibly influence many perovskite-based devices. In this work, doping of metal halide perovskites is studied by electrochemically formed Au + interstitial ions, combining experimental data on devices with a computational analysis of Au + interstitial defects based on density functional theory (DFT). Analysis suggests that Au + cations can be easily formed and migrate through the perovskite bulk via the same sites as iodine interstitials (I i + ). However, whereas I i + compensates n-type doping by electron capture, the noble-metal interstitials act as quasi-stable n-dopants. Experimentally, voltage-dependent, dynamic doping by current density-time (J-t), electrochemical impedance, and photoluminescence measurements are characterized. These results provide deeper insight into the potential beneficial and detrimental impacts of metal electrode reactions on long-term performance of perovskite photovoltaic and light-emitting diodes, as well as offer an alternative doping explanation for the valence switching mechanism of halide-perovskite-based neuromorphic and memristive devices.

Electric Field Effects in Hybrid Perovskites Studied via Picosecond Kerr Microscopy

“…One recent study also showed Rashba effects from local symmetry-breaking properties of mixed-halide mixed-cation HOIPs . Other studies show that oxidation and reduction potentials of the involved halide species dictate the specifics of this migration behavior under applied voltage. − We could assign the MA + cation to this characteristic behavior as a simple postulate. However, we do not know if the Kerr spectrum is influenced more by the MA + ions or the I – ions, as we cannot distinguish between a surplus of MA + vs an absence of I – in our measurement.…”

Direct Observation of Contact Reaction Induced Ion Migration and its Effect on Non‐Ideal Charge Transport in Lead Triiodide Perovskite Field‐Effect Transistors

“…Kerner et al have very recently observed a similar migration of Au + interstitials from an Au anode in a MAPbI 3 perovskite diode, which enhances n-type doping of the perovskite layer. [10] Pospisil et al also observed improved charge carrier injection in a two-terminal MAPbBr 3 device with AuI-modified Au electrode. [59] This proposed model can also explain the observed dependence of the current build-up effect on stoichiometry.…”

“…It has been shown that at positive potentials Au can be oxidized in the presence of iodide species leading to the electromigration of Au into the perovskite layer. [7,10] Interstitial Au + i as n-type dopant or the formation of antisite Au Pb as trap states [8] are likely to trap the photogenerated holes and result in the PL quenching. In contrast, the expected high diffusion barrier for n-type dopant Cr 2+ i may hinder its diffusion into the perovskite lattice [8] thereby causing less PL quenching.…”

“…When MAPbI 3 is in direct contact with metal surfaces, it can react with the metal to produce various products such as Pb 0 , CH 3 NH 2 , I 2 , [5] and metal ions (e.g., Au + ). [6][7][8][9][10] These reactions can occur under the influence of an electrical field and can contribute to the transformation of ions in MAPbI 3 into redox and decomposition products such as I 0 i , I + i , [11,12] CH 3 NH 2 , [7] CH 3 + and NH 3 + . [13] The complexity of these ion migration and electrochemical processes presents a challenge to the operational stability in perovskite-based optoelectronic devices.…”

Aqueous synthesis of perovskite precursors for highly efficient perovskite solar cells

“…Although perovskite solar cells (PSCs) offer the potential for low-cost fabrication and high power conversion efficiency (PCE) of 26.1% ( 1 ), defects in the perovskite layer have been a major challenge to achieve high PCEs ( 2 , 3 ), and previous studies have primarily focused on passivating these defects through additives ( 4 – 6 ) or interfacial modifications ( 7 – 9 ). In addition to defect passivation, impurities in commercial lead iodide (PbI 2 ) reagents can catalyze perovskite solution degradation and the formation of harmful by-products ( 10 ).…”