Effective Ion Mobility and Long‐Term Dark Current of Metal Halide Perovskites with Different Crystallinities and Compositions

Abstract

Perovskites have been explored in almost all fields of material science. [1,2] Considerable efforts have been made on examining the causes of hysteresis in the current-voltage curves, [3][4][5] the nature of charge traps, defects, [6,7] grain boundaries, [8] origins of ion migration, [9][10][11] not only in the field of solar cells and light emitters devices, [12] but also as key materials in fuel cells [13] and electrodes for water electrolyzers. [14] By tailoring the composition of the perovskite compounds, a variety of physical properties appears, such as ferroelectric, [15] dielectric, piezoelectric, magnetic, [16] catalytic, [17] photovoltaic, electronic-ionic-conduction, [18] and superconducting properties. [19] Recently, metal halide perovskite (HP) materials have been successfully used in X-ray imaging and ionizing radiation detectors. [20,21] The chemical formula APbX 3 (where A is a cation and X is the halide anion) comprises reasonably high Z elements, which are helpful to stop high-energy radiation photons. HPs exhibit the so-called defect tolerance which is connected to the transport properties allowing to maximize the product of the charge mobility and carrier lifetime by minimizing the bulk/surface defect density. [22][23][24] Furthermore, direct semiconductor radiation detectors based on Pb-HPs can be grown and processed in solution at relatively low temperatures and from low-cost basic raw materials. [25,26] Fast and efficient detection of hard X-and γ-ray with high energy resolution is critical for medical and industrial applications. [27] The direct conversion X-ray detectors transform the incident X-ray photons directly into electrical signals, and present an advantage in terms of high spatial resolution in comparison to indirect detectors such as CsI. [28] Besides optimization in material composition and device architecture, the conventional direct detectors, such as amorphous selenium (α-Se), [29] suffer from their low mobility-lifetime (μτ) product and small atomic number which limit their sensitivity. [24,30] In contrast, HPs exhibit large μτ-product and strong stopping power. However, the persistent drawback of ion migration results in deleterious and unstable dark current. [31][32][33] In fact, induced dark current and also

Long‐Term Field Screening by Mobile Ions in Thick Metal Halide Perovskites: Understanding Saturation Currents

“…The simplest experiment to test the long-term current response of PXDs is the measurement of chronoamperometries at different polarizations, i.e., repeating the protocol schemed in Figure 1b for different long-term voltage pulses, as in our previous works. [10][11][12]14] The corresponding simulations can be found in Figure 2a and S2a, Supporting Information, for different ranges of mobile ion concentration (N ion ) and mobility (μ ion ). Similarly, the effect of changing N ion and μ ion is presented in Figure 2b,c, respectively.…”

“…[9][10][11] Interestingly, such a behavior includes several regimes. Figure 1a shows a representative experimental chronoamperometry from our previous work [12] and Figure 1b schemes the corresponding three main current domains. First, upon application of bias voltage there is i) the electronic charge carrier response in a time scale up to the order of microseconds.…”

“…Furthermore, the shape of each regime has been found to depend on the voltage bias and nearly linear trends ( J ∝ V n , n % 1) have been reported for the saturation current. [10][11][12]14] The drift-diffusion numerical simulations are arguably the most exhaustive parameterization approach to understand the macroscopic electrical response of semiconductor devices. For decades, the numerical tools for the mostly stationary solutions of the transport equations have been well developed for devices composed by classic inorganic semiconductors [15][16][17][18] and organic materials.…”

“…Furthermore, the shape of each regime has been found to depend on the voltage bias and nearly linear trends ( J V n , n ≈ 1) have been reported for the saturation current. [ 10–12,14 ]…”

“…Adapted with permission. [ 12 ] Copyright 2022, Wiley‐VCH. b) Schemed regimes of long‐term dark reverse bias current response to polarization: i) fast electronic response, ii) ionic–electronic current activation, and iii) saturation toward steady‐state electronic current.…”