Ion Migration Effects Research Articles

Enhanced Electric Field Minimizing Quasi-Fermi Level Splitting Deficit for High-Performance Tin-Lead Perovskite Solar Cells.

The quasi-Fermi level splitting (QFLS) deficit caused by the non-radiative recombination at the interface of perovskite/electron transport layer (ETL) can lead to severe open-circuit voltage (VOC) loss and thus decreases the efficiency of perovskite solar cells (PSCs), however, has received limited attention in inverted tin-lead PSCs. Herein, the strategy of constructing an extra-electric field is presented by introducing ferroelectric polymer dipoles (FPD)-β-poly(1,1-difluoroethylene)-to suppress the QFLS deficit. The directional polarization of FPD can enhance the built-in electric field (BEF) and thus promote the charge transfer at the perovskite/ETL interface, which effectively suppresses non-radiative recombination. Furthermore, the incorporation of FPD facilitates high-quality crystallization of perovskite and reduces the surface energetic disorder. Therefore, the QFLS deficit in the perovskite/ETL half-stacked device is reduced from 62 to 27 meV after incorporating FPD, and the optimized device achieves an efficiency of 23.44% with a high VOC of 0.88V. Additionally, the addition of FPD increases the activation energy for ion migration, which can reduce the effect of ion migration on the long-term stability of the device. Consequently, the FPD-incorporated device retains 88% of the initial efficiency after 1100h of continuous illumination at the maximum power point (MPP).

Ion migration effects during hydro-fracturing of deep high salinity coal seam

Hydraulic fracturing enables effective exploitation of deep coalbed methane. During the hydraulic fracturing process, high salinity flowback fluid is generated, and this poses a significant challenge for water treatment. Therefore, we investigate the effect of hydraulic fracturing on ion migration in deep coal seams and its underlying mechanisms. In this study, nuclear magnetic resonance, inductively coupled plasma mass spectrometry, scanning electron microscopy, and energy dispersive x-ray spectroscopy were utilized to systematically study the diffusion behavior of ions and its correlation with water imbibition. Our results show that imbibition equilibrium was reached before ion diffusion finished. Ion diffusion displays three linear stages followed by a plateau part, and the second segment is the fastest one. The water–coal interactions result in the diffusion of ions into solution, with the most significant increases in Ca2+, Mg2+, Na+, K+, Li+, Cu2+, V5+, Hg2+, Pb2+, B3+, Mo6+, Cr3+, Sn4+, Cd2+, Cs+, Sr2+, and Ba2+. The dissolution of calcite, sodium feldspar, and kaolinite are the main contributions for ion migration. In addition, these reactions not only cause the release of ions into the solution but also lead to the formation of secondary pore-fractures and secondary precipitation. The results of this work help to understand better the ion migration induced by the water–coal interaction and to evaluate the fluid properties in deep coal formations.

Exploring various Integration Methods of carbon quantum dots in CsPbCl3 perovskite solar cells for enhanced power conversion efficiency

In this study, we explore the integration of carbon quantum dots (QDs) in cesium lead halide perovskite solar cells (PSCs) across the electron transport layer (ETL), hole transport layer (HTL), and the perovskite absorber to enhance power conversion efficiency (PCE). We conduct a comprehensive investigation from thin film analysis to complete device characterization, encompassing eight different device topologies. Our results reveal that the integration of QDs in various layers significantly impacts the performance of the PSCs. Notably, adding QDs in the HTL and ETL improves charge transport and reduces recombination, enhancing device efficiency. Furthermore, introducing QDs in the perovskite layer leads to modifications in the energy landscape, reducing charge trapping and enhancing stability. We observe a trade-off between short-circuit current and overall PCE, with different QD integration strategies yielding distinct performance outcomes. Additionally, incorporating QDs in the ETL layer reduces hysteresis, attributed to mitigated ion migration and charge-trapping effects. Overall, the addition of QDs in these layers demonstrates improved charge transport, reduced recombination, and enhanced stability, ultimately contributing to the enhanced performance and efficiency of perovskite solar cells, reaching 22.5%. This study paves the way for future investigations into the potential of QDs in PSC technology and their impact on device forecasting and operational stability.

Charge transport and ion migration in perovskite-incorporated conjugated polymer semiconductor

The migration of intrinsic ions in metal halide perovskites and their interfaces has been shown to contribute to hysteresis and performance degradation in perovskite-based electronic devices, particularly in photovoltaics and transistors. Accordingly, controlling the film morphology, microstructure, and ionic defects in perovskite semiconductors is essential for advancing and achieving high-performance perovskite field-effect transistors (FETs). In this study, we demonstrate a well-controlled method to systematically probe the structure-property relationships, origin of hysteresis, and intrinsic ion migration effects in formamidinium iodide and lead iodide (FAI + PbI2)-based perovskite by incorporating it in a semicrystalline conjugated poly(3-hexylthiophene) (P3HT) polymer. Optimized FETs exhibited over 100% hole mobility enhancement owing to unperturbed edge-on crystalline orientation of the P3HT chains caused by the incorporated perovskite, P3HT-(FAI + PbI2) interactions, and better charge injection properties. However, the optimized devices exhibited improved current modulation with dual-sweep hysteresis, which was attributed to the ion migration effect contributed by the polarization of the lead/iodine-related ions and defects. Furthermore, operational stability investigation of the P3HT-(FAI + PbI2) FETs in the air revealed gradual current decay owing to charge trapping in contrast to the control P3HT FETs. This work provides a fundamental understanding of the origin of hysteresis and instabilities in metal perovskite materials and their transistor-based devices.

How temperature impacts material properties and photovoltaic performance of mixed-halide perovskite via light-induced ion migration

This paper analyzes the effects of thermal and light-induced ion migration for halide perovskite. In situ measurements show that ion migration forms phase segregation and formation of iodide-rich domains, with increased carrier recombination.

Substitution of lead with tin suppresses ionic transport in halide perovskite optoelectronics.

Despite the rapid rise in the performance of a variety of perovskite optoelectronic devices with vertical charge transport, the effects of ion migration remain a common and longstanding Achilles' heel limiting the long-term operational stability of lead halide perovskite devices. However, there is still limited understanding of the impact of tin (Sn) substitution on the ion dynamics of lead (Pb) halide perovskites. Here, we employ scan-rate-dependent current-voltage measurements on Pb and mixed Pb-Sn perovskite solar cells to show that short circuit current losses at lower scan rates, which can be traced to the presence of mobile ions, are present in both kinds of perovskites. To understand the kinetics of ion migration, we carry out scan-rate-dependent hysteresis analyses and temperature-dependent impedance spectroscopy measurements, which demonstrate suppressed ion migration in Pb-Sn devices compared to their Pb-only analogues. By linking these experimental observations to first-principles calculations on mixed Pb-Sn perovskites, we reveal the key role played by Sn vacancies in increasing the iodide ion migration barrier due to local structural distortions. These results highlight the beneficial effect of Sn substitution in mitigating undesirable ion migration in halide perovskites, with potential implications for future device development.

Enhanced LED Performance by Ion Migration in Multiple Quantum Well Perovskite.

Here we study the effect of ion migration on the performance of perovskite light emitting diodes (PeLEDs). We compared aromatic and linear barrier molecules in Ruddlesden-Popper and Dion-Jacobson two-dimensional perovskites having multiple quantum well (MQW) structures. PeLED devices were fabricated by using the same conditions and architecture, while their electroluminescence properties and ion migration behavior were investigated. Impedance spectroscopy measurements were used to analyze the PeLEDs, which found a direct link between the barrier molecule type, the device efficiency, and ion migration. The best performing LEDs were based on the aromatic barriers, which present dominant inductive impedance, indicating an earlier onset voltage of radiative recombination. These findings present an approach of how to control radiative emission in perovskite LEDs which opens the way for further improvement in PeLEDs and memristors.

Effect of ion migration on lead halide perovskite on visible light communication system

Benefiting from the high modulation bandwidth (BW), low energy consumption and excellent optical performance, lead halide perovskite has attracted wide attention in visible light communication (VLC). However, the ion migration which results in mobile point defects in perovskite structures is recognized as a crucial key factor inducing the performance degradation. Here, the influence of ion migration in perovskite devices on the performance of VLC was systematically studied. The ion migration process is realized by mixing CsPbBr3 and CsPbI3 quantum dots, during which, the performance of the VLC system is reduced, but it can return to its initial state after stabilization. The on-off keying (OOK) modulation scheme of the perovskite light-emitting diode (LED) device was carried out, achieving a data rate of 90 Mbps.

Temperature-dependent ion migration and mobile-ion-induced degradation of perovskite solar cells under illumination

Effects of temperature-dependent ion migration on power reduction of perovskite solar cells (PSCs) under illumination were investigated at temperatures between 15 °C and 45 °C. Mobile-ion concentrations increased with temperature and the power reduction under illumination became faster at high temperatures due to an increase in the number of slow mobile ions and a decrease in the number of fast mobile ions, which was confirmed through ion migration currents. This indicates formation of deep-level defects with low mobility from the fast mobile ions (halide vacancies). Moreover, the transient power responses during maximum-power-point tracking (MPPT) became slower at high temperatures upon illumination, reflecting an increase in the number of slow mobile ions. Furthermore, the light–dark cycling test clarified that the energy yield during 8 h of illumination was reduced by ∼10 rel% per light–dark cycle at 45 °C, which was accompanied by an increase in the concentration of, particularly slow, mobile ions. These results indicate that transient ion-migration analysis for evaluating the concentration of mobile ions (mobile defects) can be effective in understanding the mobile-ion-induced degradation of PSCs.

Electrochemical CO2 reduction on few-atomic-layer bismuth nanosheets

This work reports on few-atomic-layer thin bismuth nanosheets (BiNSs) prepared via two-step electrodeposition method with Br-as structure-inducing-agent for electrochemical CO2 reduction towards formate. The BiNSs exhibit an impressive CO2 reduction reaction performance of large current density and high Faradic efficiency to produce formate. We further examine the effect of bicarbonate ion migration in CO2 electrochemical reduction process. The magneto-current density and thus the formate yield can be significantly increased in the presence of magnetic field. The CO2 reduction reaction on BiNSs electrodes in magnetic field processes with a high Faradic efficiency over 90% in a wide potential range from −0.68 V to −1.13 V (vs. RHE). Detailed investigation including in-situ spectroscopic analysis, isotopic labeling characterization and ultramicroelectrode voltammetric measurement reveal the total enhancement in electrochemical CO2 reduction capability on BiNSs could be mainly attributed to the magnetic field facilitated spin evolution process along with the magnetohydrodynamic effect. The contribution of spin evolution process and mass transport to the current enhancement indicates the CO2 reduction reaction process can be modulated by kinetic in the further.

Operando Characterizations of Light-Induced Junction Evolution in Perovskite Solar Cells.

Light-induced performance changes in metal halide perovskite solar cells (PSCs) have been studied intensively over the last decade, but little is known about the variation in microscopic optoelectronic properties of the perovskite heterojunctions in a completed device during operation. Here, we combine Kelvin probe force microscopy and transient reflection spectroscopy techniques to spatially resolve the evolution of junction properties during the operation of metal-halide PSCs and study the light-soaking effect. Our analysis showed a rise of an electric field at the hole-transport layer side, convoluted with a more reduced interfacial recombination rate at the electron-transport layer side in the PSCs with an n-i-p structure. The junction evolution is attributed to the effects of ion migration and self-poling by built-in voltage. Device performances are correlated with the changes of electrostatic potential distribution and interfacial carrier dynamics. Our results demonstrate a new route for studying the complex operation mechanism in PSCs.

Ion Migration and Accumulation in Halide Perovskite Solar Cells†

Comprehensive SummaryThe halide perovskite semiconductors‐based solar cells (PVSCs) show great promise as next‐generation renewable energy sources, with the merits of low cost, high performance, good flexibility, etc. A major difference distinguishing the perovskite semiconductors from others lies in their ionic feature. This intrinsic property induces “freely‐moving” ions to migrate and accumulate in the perovskite films and devices under different external stresses. As a charge carrier, these processes will strongly couple with the electronic process, and dramatically affect the performance and stability of PVSCs. This review summarizes and discusses the recent progresses and fundamental understandings of ion migration and accumulation behaviors in PVSCs. First, the basic principles of the general ion migration are reviewed. Second, following the fundamental understandings, the critical factors, e.g., ion migration activation energy, ion density, ion diffusion coefficient, etc., are extracted to understand the ion migration and accumulation in perovskite film. Third, the principles governing ion accumulation behaviors under different external stresses are discussed. Finally, the effect of ion migration and accumulation on band bending, and device performance is presented. Therefore, we hope this review provides a tutorial and insightful perspective regarding the most prominent ionic feature of perovskite semiconductors and their application for photovoltaics.

Charge transport in mixed metal halide perovskite semiconductors.

Investigation of the inherent field-driven charge transport behaviour of three-dimensional lead halide perovskites has largely remained challenging, owing to undesirable ionic migration effects near room temperature and dipolar disorder instabilities prevalent specifically in methylammonium-and-lead-based high-performing three-dimensional perovskite compositions. Here, we address both these challenges and demonstrate that field-effect transistors based on methylammonium-free, mixed metal (Pb/Sn) perovskite compositions do not suffer from ion migration effects as notably as their pure-Pb counterparts and reliably exhibit hysteresis-free p-type transport with a mobility reaching 5.4 cm2 V-1 s-1. The reduced ion migration is visualized through photoluminescence microscopy under bias and is manifested as an activated temperature dependence of the field-effect mobility with a low activation energy (~48 meV) consistent with the presence of the shallow defects present in these materials. An understanding of the long-range electronic charge transport in these inherently doped mixed metal halide perovskites will contribute immensely towards high-performance optoelectronic devices.

A Theoretical Investigation of Transport Layer‐Free Homojunction Perovskite Solar Cells via a Detailed Photoelectric Simulation

AbstractAlthough the conventional n‐i‐p or p‐i‐n perovskite solar cells (PSCs) can produce ultrahigh efficiency (>25%), complex synthesis/deposition processes together with strict requirements for preparing the hole‐ and electron‐transport layers (HTLs and ETLs) pose a challenge to accessing low‐cost perovskite devices. To address this issue, a simple strategy of employing a self‐doped perovskite homojunction to replace the HTLs and ETLs has been widely proposed. However, this type of TL‐free homojunction PSCs is usually endowed with poor efficiency. Here, the design principles and working mechanisms of the TL‐free homojunction PSCs are clarified via a rigorous photoelectric simulation. The potential of this type of device is unlocked by optimizing the structural/electrical parameters including thickness, doping concentration, bulk/interface defect concentration, contact barrier, and mobility of n‐perovskite and p‐perovskite. To further uncover the intrinsic physical behavior, ion migration, and photon recycling effects on this type of TL‐free homojunction PSCs are also studied. In addition, devices with different types of structures including TL‐free inverted, ETL‐free, and HTL‐free designs are briefly discussed. Finally, a clear roadmap for the promotion of device efficiency is proposed, providing valuable guidance for designing high‐efficient TL‐free homojunction PSCs.

Ion Migration Induced Unusual Charge Transport in Tin Halide Perovskites

Metal halide perovskites are considered next-generation semiconductors for various optoelectronic devices owing to their low-cost processability and superior optoelectronic properties. However, the performance and reliability of perovskite-based devices depend on electric-field-driven ion migration, whose mechanism remains unclear. Tin (Sn2+)-based perovskites are attracting particular interest owing to their unique charge-transport properties and eco-friendly characteristics. Here, we explore the effect of ion migration on the charge-transport properties of the Sn2+ perovskite using the transistor as the test platform. To supply mobile ions, we added copper iodide to the Sn2+ perovskite film. The ion migration and accumulation-induced electrochemical doping of the perovskite channel resulted in abnormal transitions in the electrical characteristics with the abnormally high transient field-effect mobility. We expect this study provides a hint for the decipherment of ion migration effect on the charge-transport properties of Sn2+ perovskites and the design of novel perovskite-based electronics.

Analysis of geological glasses by electron probe microanalysis under low beam current density conditions

An electron probe microanalysis method was developed to mitigate alkali ion migration effects under low beam current density conditions with a time-saving mode to collect alkali-ion X-ray signals. The method is suitable for estimating H2O content in H2O-rich geological glasses as a substitute technique for SIMS and FTIR.

Detour-phased perovskite ultrathin planar lens using direct femtosecond laser writing

Perovskite-enabled optical devices have drawn intensive interest and have been considered promising candidates for integrated optoelectronic systems. As one of the important photonic functions, optical phase modulation previously was demonstrated with perovskite substrate and complex refractive index engineering with laser scribing. Here we report on the new scheme of achieving efficient phase modulation by combining detour phase design with 40 nm ultrathin perovskite films composed of nanosized crystalline particles. Phase modulation was realized by binary amplitude patterning, which significantly simplifies the fabrication process. Perovskite nanocrystal films exhibit significantly weak ion migration effects under femtosecond laser writing, resulting in smooth edges along the laser ablated area and high diffractive optical quality. Fabrication of a detour-phased perovskite ultrathin planar lens with a diameter of 150 μm using femtosecond laser scribing was experimentally demonstrated. A high-performance 3D focus was observed, and the fabrication showed a high tolerance with different laser writing powers. Furthermore, the high-quality imaging capability of perovskite ultrathin planar lenses with a suppressed background was also demonstrated.

Perfluoroarenes: A Versatile Platform for Hybrid Perovskite Photovoltaics.

The instability of hybrid organic-inorganic halide perovskites presents one of the pressing challenges for their application. This is associated with the sensitivity to moisture as well as mixed ionic-electronic conductivity that leads to enhanced ion migration under conditions of voltage and light bias. Some of the most effective strategies to stabilize hybrid perovskite materials during operation involve the use of interfacial molecular assemblies and low-dimensional perovskite architectures based on hydrophobic organic moieties that could suppress the effects of moisture or ion migration. For this purpose, perfluoroarenes have provided a versatile platform due to their enhanced hydrophobicity as well as the capacity to engage in various noncovalent interactions that affect the characteristics of the resulting assemblies as well as ion migration. This Perspective discusses the emerging role of perfluoroarenes in stabilizing hybrid perovskite materials and their photovoltaic devices through different modes of action, offering insights for the design of advanced materials.

Ion Migration in the All-Inorganic Perovskite CsPbBr3 and Its Impacts on Photodetection

Ion migration has been widely investigated in the lead halide perovskites, which severely deteriorates the performance of solar cells. However, the impacts of ion migration on photodetection have been rarely studied so far. In the current work, ion migration in the all-inorganic perovskite CsPbBr3 and its impacts on photodetection have been investigated in detail. Electrical property studies showed that ion migration has occurred under an external electric field poling, which led to the formation of a pn-junction within the CsPbBr3 single crystals. Density function theory calculations have shown that vacancy-assisted Br-ion migration dominated the ion transportation processes. Accordingly, the Au/CsPbBr3/Au metal–semiconductor–metal structured photodetectors showed a decreased performance in terms of a decreased on–off ratio and decreased detectivity through a long-term operation under a bias voltage, although the photoresponsivity slightly increased simultaneously. The results provided in this work verify the negative effects of ion migration in the all-inorganic perovskite CsPbBr3, which may account for the instability of CsPbBr3-based optoelectronic devices reported in the literature.

Ion Migration in Perovskite Light-Emitting Diodes: Mechanism, Characterizations, and Material and Device Engineering.

In recent years, perovskite light-emitting diodes (PeLEDs) have emerged as a promising new lighting technology with high external quantum efficiency, color purity, and wavelength tunability, as well as, low-temperature processability. However, the operational stability of PeLEDs is still insufficient for their commercialization. The generation and migration of ionic species in metal halide perovskites has been widely acknowledged as the primary factor causing the performance degradation of PeLEDs. Herein, this topic is systematically discussed by considering the fundamental and engineering aspects of ion-related issues in PeLEDs, including the material and processing origins of ion generation, the mechanisms driving ion migration, characterization approaches for probing ion distributions, the effects of ion migration on device performance and stability, and strategies for ion management in PeLEDs. Finally, perspectives on remaining challenges and future opportunities are highlighted.