Probing the ionic defect landscape in halide perovskite solar cells

Reichert, Sebastian; An, Qingzhi; Woo, Young Won; Walsh, Aron; Vaynzof, Yana; Deibel, Carsten

doi:10.1038/s41467-020-19769-8

Cited by 89 publications

(100 citation statements)

References 94 publications

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“…At room temperature, the V + I concentration N 0 = 0.4% = 1.6×10 19 cm −3 for a cubic unit cell with lattice constant a = 0.628 nm, 22,23 . Eames et al 22 estimated E A for V + I as 0.58 eV for cubic MAPI (similar to the more recent value of 0.55 eV 24 ). They find a much higher E A of 0.84 eV for V − MA migration, given that its path is through the unit cell face or through a bottleneck comprising four I − ions, and E A of 2.31 eV for V − Pb , suggesting an immobile Pb sublattice.…”

Section: Introductionsupporting

confidence: 60%

Deducing transport properties of mobile vacancies from perovskite solar cell characteristics

Cave

Courtier

Blakborn

et al. 2020

Journal of Applied Physics

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The absorber layers in perovskite solar cells possess a high concentration of mobile ion vacancies. These vacancies undertake thermally activated hops between neighbouring lattice sites. The mobile vacancy concentration N 0 is much higher and the activation energy E A for ion hops is much lower than is seen in most other semiconductors due to the inherent softness of perovskite materials. The timescale at which the internal electric field changes due to ion motion is determined by the vacancy diffusion coefficient D v and is similar to the timescale on which the external bias changes by a significant fraction of the open circuit voltage at typical scan rates. Therefore hysteresis is often observed in which the shape of the current-voltage, J-V, characteristic depends on the direction of the voltage sweep. There is also evidence that this defect motion plays a role in degradation. By employing a charge transport model of coupled ion-electron conduction in a perovskite solar cell, we show that E A for the ion species responsible for hysteresis can be obtained directly from measurements of the temperature variation of the scan-rate dependence of short-circuit current and of the hysteresis factor H. This argument is validated by comparing E A deduced from measured J-V curves for four solar cell structures with density functional theory calculations. In two of these structures the perovskite is MAPbI 3 (MAPI) where MA is methylammonium, CH 3 NH 3 , the hole transport layer (HTL) is spiro (spiro-OMeTAD, 2,2',7,7'tetrakis[N,N-di(4-methoxyphenyl) amino]-9,9'-spirobifluorene) and the electron transport layer (ETL) is TiO 2 or SnO 2 . For the third and fourth structures, the perovskite layer is FAPbI 3 (FAPI) where FA is formamidinium, HC(NH 2 ) 2 , or MAPbBr 3 (MAPBr) and in both cases the HTL is spiro and the ETL is SnO 2 . For all four structures, the hole and electron extracting electrodes are Au and FTO (fluorine doped tin oxide) respectively. We also use our model to predict how the scan rate dependence of the power conversion efficiency varies with E A , N 0 and parameters determining free charge recombination.

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Section: Introductionsupporting

confidence: 60%

Deducing transport properties of mobile vacancies from perovskite solar cell characteristics

Cave

Courtier

Blakborn

et al. 2020

Journal of Applied Physics

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“…Nevertheless, it is generally accepted that the halide ions are the fastest mobile ion species. Measured diffusion coefficients for halide ions in MAPbI 3 range from 10 -6 to 10 -9 cm 2 /s at room temperature and the spread in values was shown to follow the Mayer-Nudel rule (Reichert et al, 2020a). This is much faster than mobile MA + ions, with typical diffusion coefficients between 10 -10 to and 10 -12 cm 2 /s (Yuan et al, 2015;Futscher et al, 2019).…”

Section: Phenomenologymentioning

confidence: 88%

Mixed Conductivity of Hybrid Halide Perovskites: Emerging Opportunities and Challenges

Futscher

Milić

2021

Front. Energy Res.

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Hybrid halide perovskites feature mixed ionic-electronic conductivities that are enhanced under device operating conditions. This has been extensively investigated over the past years by a wide range of techniques. In particular, the suppression of ionic motion by means of material and device engineering has been of increasing interest, such as through compositional engineering, using molecular modulators as passivation agents, and low-dimensional perovskite materials in conjunction with alternative device architectures to increase the stabilities under ambient and operating conditions of voltage bias and light. While this remains an ongoing challenge for photovoltaics and light-emitting diodes, mixed conductivities offer opportunities for hybrid perovskites to be used in other technologies, such as rechargeable batteries and resistive switches for neuromorphic memory elements. This article provides an overview of the recent developments with a perspective on the emerging utility in the future.

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“…The TID method can detect both moving cations and anions, which is a unique advantage in investigating the ion migration process compared with TDC [21][22][23][24] and IS [25][26][27] measurements. The TID method is well established in PSCs by Futscher et al [28][29][30][31] and Reichert et al [32,33] The TID method was conducted on mixed-composition perovskite (PEABr 0.2 Cs 0.4 MA 0.6 PbBr 3 ) by Futscher et al [29] However, as PEABr 0.2 Cs 0.4 MA 0.6 PbBr 3 is typically used for light-emitting diodes (LEDs), the influence of ion migration on mixed-composition PSCs has not been further studied. [29] Because of the unique advantage of the TID method, it provides a great platform for investigating the influence of the migration of both cations and anions on mixed-composition PSCs.…”

mentioning

confidence: 99%

Understanding the Influence of Cation and Anion Migration on Mixed‐Composition Perovskite Solar Cells via Transient Ion Drift

Kan

Hang

et al. 2021

Physica Rapid Research Ltrs

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In just a decade, the power conversion efficiency (PCE) of perovskite solar cells (PSCs) has increased from 3.8 [1] to 25.5%. [2] However, the most critical challenge preventing PSCs from being the next generation of solar cells is their poor longterm stability. [3,4] Ion migration has been identified as one of the most important causes of this poor stability. [5][6][7] It has been hypothesized by some researchers that ion migration in light-harvesting layers screens the built-in potential, leading to the anomalous hysteresis phenomenon [8,9] and the accumulation of ions at the interface between perovskite and transporting layers, thus modifying the band diagram of the devices and leading to degradation of the PSCs. [9,10] Furthermore, if mobile ions (MA þ , I À ) out-diffuse to transporting layers, or even to metal electrodes, it will result in a deterioration of the cell performance either by generating deep-level trap states in transporting layers or by an enhanced chemical reaction with transporting materials or electrodes. [11][12][13] MAPbI 3 is a prototype perovskite material used to fabricate PSCs. However, it suffers from ion migration and poor stability. [14,15] To overcome these problems, researchers have used a composition modulation strategy to alleviate ion migration in PSCs, attempting to achieve PSC devices with better performance and better long-term stability. Typically, perovskite compositions with a combination of mixed cations (FA þ , MA þ ) and mixed anions (Br À , I À ) were used to produce PSC devices with reduced hysteresis and better stability. [16] In addition, a small amount of Cs þ ions were added to the perovskite layers to improve the reproducibility and stability of PSCs because Cs þ ions are suggested to stabilize the crystal structure of perovskite. [17,18] Hence, mixed-composition perovskites with mixed cations and anions have been extensively studied and applied in the scope of PSCs, resulting in state-of-the-art PSCs. [19,20] Different methods, such as temperature-dependent conductivity (TDC) measurements [21][22][23][24] and impedance spectroscopy (IS) measurements, [25][26][27] are used to investigate the ion migration process in PSCs. Kim et al. [25] carried out IS measurements on both (FAPbI 3 ) 0.875 (CsPbBr 3 ) 0.125 and MAPbI 3 films.

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Probing the ionic defect landscape in halide perovskite solar cells

Cited by 89 publications

References 94 publications

Deducing transport properties of mobile vacancies from perovskite solar cell characteristics

Deducing transport properties of mobile vacancies from perovskite solar cell characteristics

Mixed Conductivity of Hybrid Halide Perovskites: Emerging Opportunities and Challenges

Understanding the Influence of Cation and Anion Migration on Mixed‐Composition Perovskite Solar Cells via Transient Ion Drift

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