Self‐Regulation Mechanism for Charged Point Defects in Hybrid Halide Perovskites

Walsh, Aron; Scanlon, David O.; Chen, Shiyou; Gong, X. G.; Wei, Su‐Huai

doi:10.1002/ange.201409740

Cited by 172 publications

(149 citation statements)

References 28 publications

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“…In principle this can then be used to estimate the ion density, although presently a large range of ionic diffusion constants (1 × 10 −8 cm 2 s −1 to 1 × 10 −12 cm 2 s −1 for the iodide vacancy in MAPbI 3 ) [72,73] hinders the accuracy of this step. Observations of a loop feature at approximately 1 kHz [43] in this sense suggest ion densities between 1 × 10 17 cm −3 to 1 × 10 21 cm −3 , which is at least in approximately the expected range [33]. Fig 3a shows a simulated impedance spectrum featuring an "inductive loop" at intermediate frequencies, produced by including a net acceptor doping density at a significant fraction of the mean ion density (N A = 4 × 10 17 cm −3 with N ion = 1 × 10 18 cm −3 ).…”

Section: Loop Features and Negative Capacitancementioning

confidence: 72%

The two faces of capacitance: New interpretations for electrical impedance measurements of perovskite solar cells and their relation to hysteresis

Jacobs

Shen

Pfeffer

et al. 2018

Journal of Applied Physics

127

137

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Perovskite solar cells are notorious for exhibiting transient behaviour not seen in conventional inorganic semiconductor devices. Significant inroads have been made into understanding this fact in terms of rapid ion migration, now a well-established property of the prototype photovoltaic perovskite MAPbI3 and strongly implicated in the newer mixed compositions. Here we study the manifestations of ion migration in frequency-domain small-signal measurements, focusing on the popular technique of Electrical Impedance Spectroscopy (EIS). We provide new interpretations for a variety of previously puzzling features, including giant photo-induced low-frequency capacitance and negative capacitance in a variety of forms. We show that these apparently strange measurements can be rationalized by the splitting of AC current into two components, one associated with charge-storage, and the other with the quasi-steady-state recombination current of electrons and holes. The latter contribution to the capacitance can take either a positive or a negative sign, and is potentially very large when slow, voltage-sensitive processes such as ion migration are at play. Using numerical drift-diffusion semiconductor models, we show that giant photo-induced capacitance, inductive loop features, and low-frequency negative capacitance all emerge naturally as consequences of ion migration via its coupling to quasi-steady-state electron and hole currents. In doing so, we unify the understanding of EIS measurements with the comparably well-developed theory of rate dependent current-voltage (I-V) measurements in perovskite cells. Comparing the two techniques, we argue that EIS is more suitable for quantifying I-V hysteresis than conventional methods based on I-V sweeps, and demonstrate this application on a variety of cell types.

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Section: Loop Features and Negative Capacitancementioning

confidence: 72%

The two faces of capacitance: New interpretations for electrical impedance measurements of perovskite solar cells and their relation to hysteresis

Jacobs

Shen

Pfeffer

et al. 2018

Journal of Applied Physics

127

137

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“…Our calculations are based on VASP's implementation [21] of density functional theory with the projector augmented waves method [22] parameterization was used to describe the exchange-correlation, which is more suited to describe solids' properties [20,[24][25][26][27]. Plane waves with kinetic energy cutoff of 500 eV were used to expand the wavefunctions, with larger cutoff of 600 eV leading to changes of ~ 0.05 eV in the formation energies.…”

Section: Methodsmentioning

confidence: 99%

Sc and Nb dopants in SrCoO3 modulate electronic and vacancy structures for improved water splitting and SOFC cathodes

Tahini

Tan

Zhou

et al. 2017

Energy Storage Materials

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SrCoO 3 is a promising material in the field of electrocatalysis. Difficulties in synthesising the material in its cubic phase have been overcome by doping it with Sc and Nb ions [Mater. Horiz. 2015, 2, 495-501]. Using ab initio calculations and special quasi random structures we undertake a systematic study of these dopants in order to elucidate the effect of doping on electronic structure of the SrCoO 3 host and the formation of oxygen vacancies. We find that while the overall electronic structure of SrCoO 3 is preserved, increasing the Sc fraction leads to a decrease of electrical conductivity, in agreement with earlier experimental work. For low Sc and Nb doping fractions we find that the oxygen vacancy formation increases relative to undoped SrCoO 3 . However, as the dopants concentration is increased the vacancy formation energy drops significantly, indicating a strong tendency to accommodate high concentration of oxygen vacancies and hence non-stoichiometry. This is explained based on the electronic instabilities caused by the presence of Sc ions which weakens the B-O interactions as well as the increased degree of electron delocalization on the oxygen sublattice. Sc dopants also shift the p-band centre closer to the Fermi level, which can be associated with experimentally reported improvements in oxygen evolution reactions. These findings provide crucial baseline information for the design of better electrocatalysts for oxygen evolution reactions as well as fuel-cell cathode materials.

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“…[ 25,[51][52][53] These perovskite materials with tuned band gap possess varied Fermi Energy, which affects the selection of the carrier extraction materials. [ 28,[64][65][66][67] In the following section, a thorough review is provided focusing on the carrier behavior across the interfaces and the resultant electric fi eld distribution within different device Adv. It is worthy to mention that although the Sn-based perovskite seems to be appealing low band-gap lead free light harvesters, they are limited due to the intrinsic defects, high background carrier density and poor stability.…”

Section: Working Mechanismmentioning

confidence: 99%

The Progress of Interface Design in Perovskite‐Based Solar Cells

Fan

Huang

Wang

et al. 2016

Advanced Energy Materials

144

117

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Figure 20. a) Modeled J − V characteristics of a perovskite device comprising ions but no traps. b) Modeled I -V characteristics of perovskite devices comprising ions and no traps for varying ion densities. c) Modeled J − V characteristics of perovskite device comprising ions and traps with varying ion mobility as indicated in the legend at a sweep rate of 100 kV s −1 . d) Modeled J -V characteristics of a perovskite device comprising ions and bulk traps. [ 211 ] 2015, American Chemical Society. e) Flow directions of the charged ion species in a Pb|MAPbI 3 |AgI |Ag cell under electrical bias. f) Images for surfaces A and B and g) a scanning electron microscope (SEM) image of surface B on the Pb pellet. h) The same cell confi guration to Figure 23 e. i) Images of each pellets after aging at 50 °C for a week in Ar atmosphere (no current stressing). Reproduced with permission. [ 212 ]

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Self‐Regulation Mechanism for Charged Point Defects in Hybrid Halide Perovskites

Cited by 172 publications

References 28 publications

The two faces of capacitance: New interpretations for electrical impedance measurements of perovskite solar cells and their relation to hysteresis

The two faces of capacitance: New interpretations for electrical impedance measurements of perovskite solar cells and their relation to hysteresis

Sc and Nb dopants in SrCoO3 modulate electronic and vacancy structures for improved water splitting and SOFC cathodes

The Progress of Interface Design in Perovskite‐Based Solar Cells

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