Synergy between Ion Migration and Charge Carrier Recombination in Metal-Halide Perovskites

Tong, Chuan‐Jia; Li, Linqiu; Liu, Li Min; Prezhdo, Oleg V.

doi:10.1021/jacs.9b12391

Cited by 101 publications

(91 citation statements)

References 69 publications

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“…[ 27–28 ] Considering the halide ion migration is facilitated by lattice distortion and halide vacancy formation, the deformability (or rigidity) of the frameworks as a function of halide composition directly affects the halide ion mobility. [ 29 ] As Cl content in the mixed halide perovskite increases, the more rigid, thermodynamically stabilized [PbX 6 ] 4− framework is expected to make halide ion migration difficult.…”

Section: Resultsmentioning

confidence: 99%

Photoinduced Phase Segregation in Mixed Halide Perovskites: Thermodynamic and Kinetic Aspects of Cl–Br Segregation

Cho

Kamat

2020

Advanced Optical Materials

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Suppression of halide ion mobility remains a key issue in defining the device performances and stability of perovskite solar cells. The halide ion migration is facilitated by the lattice‐distortion‐mediated halide vacancy and hence dictated by the polarizability (or rigidity) of the halide sublattice and framework. Photoinduced halide ion segregation and dark recovery of MAPb(Cl0.5Br0.5)3 films are now probed. The temperature dependence of the rate constants of segregation and dark remixing allow to determine the activation energy barriers (Ea) for photosegregation (38 kJ mol−1) and dark recovery (42 kJ mol−1). A comparison of the segregation activation energy (Ea) and excitation intensity threshold between MAPb(Cl0.5Br0.5)3 and MAPb(Br0.5I0.5)3 films reflects that the presence of Cl stabilizes mixed halide composition. The thermodynamic stabilization is attributed to the formation of more rigid [PbX6]4− frameworks with an increased barrier for halide ion migration. The thermodynamic rationale behind the intriguing halide ion mobility offers a fundamental insight into the role of Cl and design principle of perovskite solar cells with improved efficiency and long‐term stability.

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Section: Resultsmentioning

confidence: 99%

Photoinduced Phase Segregation in Mixed Halide Perovskites: Thermodynamic and Kinetic Aspects of Cl–Br Segregation

Cho

Kamat

2020

Advanced Optical Materials

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“…[ 24,25 ] This can disintegrate the perovskite crystal structure and proliferate defects to significantly deteriorate the operational stability of the device. [ 11,26,27 ]…”

Section: Introductionmentioning

confidence: 99%

Green Perovskite Light‐Emitting Diodes with 200 Hours Stability and 16% Efficiency: Cross‐Linking Strategy and Mechanism

Han

Yuan

Cai

et al. 2021

Adv Funct Materials

105

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According to the thinner emitting layer and stronger electric field in perovskite light‐emitting diodes (PeLEDs) than those in perovskite solar cells, the strong electric‐field‐driven ion‐migration is a key issue for the operational stability of PeLEDs. Here, a methylene‐bis‐acrylamide cross‐linking strategy is proposed to both passivate defects and suppress ion‐migration with an emphasis on the suppressing mechanism via in situ investigations. As typical results, in addition to the enhanced external quantum efficiency (EQE, 16.8%), PeLEDs exhibit preferable operational stability with a half lifetime (T50) of 208 h under continuous operation with an initial luminance of 100 cd m−2. Moreover, the EQE of cross‐linked LEDs can maintain above 15% during 25 times scanning as the devices are measured every 4 days. To the authors’ knowledge, this is the highest stability published until now for high‐efficiency PeLEDs with EQE over 15%. The in situ/ex situ mechanism investigation demonstrates that such cross‐linking increases binding energy from 0.54 to 0.92 eV and activation energy from 0.21 to 0.5 eV. Hence, it suppresses ligands breaking away and ion migration, which prevents ions from moving inside and across crystals. The proposed cross‐linking passivation strategy thus provides an effective methodology to fabricate stable perovskites‐based photoelectric devices.

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“…While mobile ions are not always associated with less stable devices, they have been shown to impose constraints on cell performance and stability assessment 11 and can result in a lower efficiency with the same concentration of defects compared to the same device without ions 12 . Furthermore, vacancy migration accelerates non radiative charge recombination by inducing lattice distortions 13 and perovskite layers and their interfaces with transport layers are degraded by the strain in the perovskite lattice 14 .…”

Section: Introductionmentioning

confidence: 99%

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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Synergy between Ion Migration and Charge Carrier Recombination in Metal-Halide Perovskites

Cited by 101 publications

References 69 publications

Photoinduced Phase Segregation in Mixed Halide Perovskites: Thermodynamic and Kinetic Aspects of Cl–Br Segregation

Photoinduced Phase Segregation in Mixed Halide Perovskites: Thermodynamic and Kinetic Aspects of Cl–Br Segregation

Green Perovskite Light‐Emitting Diodes with 200 Hours Stability and 16% Efficiency: Cross‐Linking Strategy and Mechanism

Deducing transport properties of mobile vacancies from perovskite solar cell characteristics

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