Understanding charge transport in lead iodide perovskite thin-film field-effect transistors

2D Printed Plasmonic Nanoparticle Array Incorporated Formamidinium-Based High-Performance Self-Biased Perovskite Photodetector

Utilizing noble metal nanoparticles through novel technologies is a promising avenue for enhancing the performance of organic/inorganic photodetectors. This study investigates the performance enhancement of Formamidinium-based perovskite (Pe) photodetectors (PDs) through the incorporation of plasmonic silver nanoparticles (Ag NPs) arrays using a 2D printing technique. The incorporation of plasmonic Ag NPs leads to a major improvement in the performance of the planar PD device, which is attributed to increased light absorption, hot electron generation, and more efficient charge extraction and transport. The unique aspect of this study lies in the method of incorporating plasmonic NPs using a two-dimensional printing technology. This approach offers several advantages over traditional methods, including lower cost, nonvacuum operation, and compatibility with room temperature fabrication. The printed plasmon-enhanced optimized perovskite PD exhibits remarkable performance metrics, including a peak responsivity of 1.03 A/W at 5 V external bias, which is significantly high compared to the reported devices. Moreover, the PD demonstrates exceptional detectivity with a peak value of 3.7 × 1012 Jones at 5 V, highlighting its capability to detect ultralow light signals with high precision. The device can be reversibly switched between low and high conductance states, yielding a stable and repeatable Ilight/Idark ratio of 1.06 × 104. In addition, the integration of plasmonic nanoparticles imparts remarkable photovoltaic characteristics to the perovskite photodetector, enabling it to function as a self-biased device. The hybrid device demonstrates a peak responsivity of 15 mA/W, a high detectivity of 2.15 × 1011 Jones, and a significant on-off ratio of 2.23 × 103, all achieved at zero external bias. Overall, this study presents a significant advancement in the field of plasmon-enhanced Pe photodetection technology. By utilizing the benefits of printing technology to incorporate NPs, we have developed a high-performance PD that combines cost-effectiveness with exceptional performance. Thus, we believe that this study will pave the way for the development of a low-cost, high-performance plasmon-enhanced Pe-based PD.

Anisotropy of Anion Diffusion in All-Inorganic Perovskite Single Crystals

Ion diffusion is a fundamentally important process in understanding and manipulating the optoelectronic properties of semiconductors. Most current studies on ionic diffusion have been focusing on perovskite polycrystalline thin films and nanocrystals. However, the random orientation and grain boundaries can heavily interfere with the kinetics of ion diffusion, where the experimental results only reveal the average ion exchange kinetics and the actual ion diffusion mechanisms perpendicular to the direction of individual crystal facets remain unclear. Here, the anion (Cl, I) diffusion anisotropy on (111) and (100) facets of CsPbBr3 single crystals is demonstrated. The as-grown single crystals with (111) and (100) facets exhibit anisotropic growth with different halide incorporation, which lead to different resulting optoelectronic properties. Combined experimental characterizations and theoretical calculations reveal that the (111) CsPbBr3 shows a faster anion diffusion behavior compared with that of the (100) CsPbBr3, with a lower diffusion energy barrier, a larger built-in electric field, and lower inverse defect formation energy. The work highlights the anion diffusion anisotropic mechanisms perpendicular to the direction of individual crystal facets for optimizing and designing perovskite optoelectronic devices.

Surface heterojunction based on n-type low-dimensional perovskite film for highly efficient perovskite tandem solar cells

Enhancing the quality of junctions is crucial for optimizing carrier extraction and suppressing recombination in semiconductor devices. In recent years, metal halide perovskite has emerged as the most promising next-generation material for optoelectronic devices. However, the construction of high-quality perovskite junctions, as well as characterization and understanding of their carrier polarity and density, remains a challenge. In this study, using combined electrical and spectroscopic characterization techniques, we investigate the doping characteristics of perovskite films by remote molecules, which is corroborated by our theoretical simulations indicating Schottky defects consisting of double ions as effective charge dopants. Through a post-treatment process involving a combination of biammonium and monoammonium molecules, we create a surface layer of n-type low-dimensional perovskite. This surface layer forms a heterojunction with the underlying 3D perovskite film, resulting in a favorable doping profile that enhances carrier extraction. The fabricated device exhibits an outstanding open-circuit voltage (VOC) up to 1.34 V and achieves a certified efficiency of 19.31% for single-junction wide-bandgap (1.77 eV) perovskite solar cells, together with significantly enhanced operational stability, thanks to the improved separation of carriers. Furthermore, we demonstrate the potential of this wide-bandgap device by achieving a certified efficiency of 27.04% and a VOC of 2.12 V in a perovskite/perovskite tandem solar cell configuration.

Enhancing Stability and Performance in Tin-Based Perovskite Field-Effect Transistors Through Hydrogen Bond Suppression of Organic Cation Migration

Ion migration poses a substantial challenge in perovskite transistors, exerting detrimental effects on hysteresis and operational stability. This study focuses on elucidating the influence of ion migration on the performance of tin-based perovskite field-effect transistors (FETs). It is revealed that the high background carrier density in FASnI3 FETs arises not only from the oxidation of Sn2+ but also from the migration of FA+ ions. The formation of hydrogen bonding between FA+ and F- ions efficiently inhibits ion migration, leading to a reduction in background carrier density and an improvement in the operational stability of the transistors. The strategy of hydrogen bond is extended to fluorine-substituted additives to improve device performance. The incorporation of 4-fluorophenethylammonium iodide additives into FETs significantly minimizes the shift of turn-on voltage during cyclic measurements. Notably, an effective mobility of up to 30 cm2 V-1 s-1 with an Ion/off ratio of 107 is achieved. These findings hold promising potential for advancing tin-based perovskite technology in the field of electronics.

Unveiling the role of linear alkyl organic cations in 2D layered tin halide perovskite field-effect transistors

Two-dimensional (2D) tin halide perovskites are promising semiconductors for field-effect transistors (FETs) owing to their fascinating electronic properties. However, the correlation between the chemical nature of organic cations and charge carrier transport is still far from understanding. In this study, the influence of chain length of linear alkyl ammonium cations on film morphology, crystallinity, and charge transport in 2D tin halide perovskites is investigated. The carbon chain lengths of the organic spacers vary from propylammonium to heptanammonium. The increase of alkyl chain length leads to enhanced local charge carrier transport in the perovskite film with mobilities of up to 8 cm2 V-1 s-1, as confirmed by optical-pump terahertz spectroscopy. A similar improved macroscopic charge transport is also observed in FETs, only to the chain length of HA, due to the synergistic enhancement of film morphology and molecular organization. While the mobility increases with the temperature rise from 100 K to 200 K due to the thermally activated transport mechanism, the device performance decreases in the temperature range of 200 K to 295 K because of ion migration. These results provide guidelines on rational design principles of organic spacer cations for 2D tin halide perovskites and contribute to other optoelectronic applications.

Progress and Application of Halide Perovskite Materials for Solar Cells and Light Emitting Devices

Halide perovskite materials have attracted worldwide attention in the photovoltaic area due to the rapid improvement in efficiency, from less than 4% in 2009 to 26.1% in 2023 with only a nanometer lever photo-active layer. Meanwhile, this nova star found applications in many other areas, such as light emitting, sensor, etc. This review started with the fundamentals of physics and chemistry behind the excellent performance of halide perovskite materials for photovoltaic/light emitting and the methods for preparing them. Then, it described the basic principles for solar cells and light emitting devices. It summarized the strategies including nanotechnology to improve the performance and the application of halide perovskite materials in these two areas: from structure-property relation to how each component in the devices affects the overall performance. Moreover, this review listed the challenges for the future applications of halide perovskite materials.

Photoinduced Nonvolatile Memory Transistor Based on Lead-Free Perovskite Incorporating Fused π-Conjugated Organic Ligands

Perovskites field-effect transistors (PeFETs) have been intensively investigated for their application in detector and synapse. However, synapse based on PeFETs is still very difficult to integrate excellent charge carrier transporting ability, photosensitivity, and nonvolatile memory effects into one device, which is very important for developing bionic electronic devices and edge computing. Here, two-dimensional (2D) perovskites are synthesized by incorporating fused π-conjugated pyrene-O-ethyl-ammonium (POE) ligands and a systematic study is conducted to obtain enhanced performance and reliable PeFETs. The optimized (POE)2 SnI4 transistors display the hole mobility over 0.3 cm2  V-1  s-1 , high repeatability, and operational stability. Meanwhile, the derived photo memory devices show remarkable photoresponse, with a switching ratio higher than 105 , high visible light responsivity (>4 × 104  A W-1 ), and stable storage-erase cycles, as well as competitive retention performance (104  s). The photoinduced memory behavior can be benefiting from the insulating nature of quantum-well in 2D perovskite under dark and its excellent light sensitivity. The excellent photo memory behaviors have been maintained after 40 days in a N2 atmosphere. Finally, a 2D perovskite-only transistors with a multi-level memory behavior (16 distinct states) is described by controlling incident light pulse. This work provides broader attention toward 2D perovskite and optoelectronic application.

Inhibition of Ion Migration for Highly Efficient and Stable Perovskite Solar Cells

In recent years, organic-inorganic halide perovskites are now emerging as the most attractive alternatives for next-generation photovoltaic devices, due to their excellent optoelectronic characteristics and low manufacturing cost. However, the resultant perovskite solar cells (PVSCs) are intrinsically unstable owing to ion migration, which severely impedes performance enhancement, even with device encapsulation. There is no doubt that the investigation of ion migration and the summarization of recent advances in inhibition strategies are necessary to develop "state-of-the-art" PVSCs with high intrinsic stability for accelerated commercialization. This review systematically elaborates on the generation and fundamental mechanisms of ion migration in PVSCs, the impact of ion migration on hysteresis, phase segregation, and operational stability, and the characterizations for ion migration in PVSCs. Then, many related works on the strategies for inhibiting ion migration toward highly efficient and stable PVSCs are summarized. Finally, the perspectives on the current obstacles and prospective strategies for inhibition of ion migration in PVSCs to boost operational stability and meet all of the requirements for commercialization success are summarized.

Ambient-Stable 2D Dion-Jacobson Phase Tin Halide Perovskite Field-Effect Transistors with Mobility over 1.6 Cm2 V-1 s-1

Solution-processed metal halide perovskites hold immense potential for the advancement of next-generation field-effect transistors (FETs). However, the instability of perovskite-based transistors has impeded their progress and practical applications. Here, ambient-stable high-performance FETs based on 2D Dion-Jacobson phase tin halide perovskite BDASnI4 , which has high film quality and excellent electrical properties, are reported. The perovskite channels are established by engineering the film crystallization process via the employment of ammonium salt interlayers and the incorporation of NH4 SCN additives within the precursor solution. The refined FETs demonstrate field-effect hole mobilities up to 1.61 cm2 V-1 s-1 and an on/off ratio surpassing 106 . Moreover, the devices show impressive operational and environmental stability and retain their functional performance even after being exposed to ambient conditions with a temperature of 45 °C and humidity of 45% for over 150 h.

Direct Observation of Contact Reaction Induced Ion Migration and its Effect on Non-Ideal Charge Transport in Lead Triiodide Perovskite Field-Effect Transistors

The migration of ionic defects and electrochemical reactions with metal electrodes remains one of the most important research challenges for organometal halide perovskite optoelectronic devices. There is still a lack of understanding of how the formation of mobile ionic defects impact charge carrier transport and operational device stability, particularly in perovskite field-effect transistors (FETs), which tend to exhibit anomalous device characteristics. Here, the evolution of the n-type FET characteristics of one of the most widely studied materials, Cs0.05 FA0.17 MA0.78 PbI3, is investigated during repeated measurement cycles as a function of different metal source-drain contacts and precursor stoichiometry. The channel current increases for high work function metals and decreases for low work function metals when multiple cycles of transfer characteristics are measured. The cycling behavior is also sensitive to the precursor stoichiometry. These metal/stoichiometry-dependent device non-idealities are correlated with the quenching of photoluminescence near the positively biased electrode. Based on elemental analysis using electron microscopy the observations can be understood by an n-type doping effect of metallic ions that are created by an electrochemical interaction at the metal-semiconductor interface and migrate into the channel. The findings improve the understanding of ion migration, contact reactions, and the origin of non-idealities in lead triiodide perovskite FETs.

Optical Memory, Switching, and Neuromorphic Functionality in Metal Halide Perovskite Materials and Devices

Metal halide perovskite based materials have emerged over the past few decades as remarkable solution-processable optoelectronic materials with many intriguing properties and potential applications. These emerging materials have recently been considered for their promise in low-energy memory and information processing applications. In particular, their large optical cross-sections, high photoconductance contrast, large carrier-diffusion lengths, and mixed electronic/ionic transport mechanisms are attractive for enabling memory elements and neuromorphic devices that are written and/or read in the optical domain. Here, recent progress toward memory and neuromorphic functionality in metal halide perovskite materials and devices where photons are used as a critical degree of freedom for switching, memory, and neuromorphic functionality is reviewed.

Recent Progress of Layered Perovskite Solar Cells Incorporating Aromatic Spacers

Layered two dimensional (2D) or quasi-2D perovskites are emerging photovoltaic materials due to their superior environment and structure stability in comparison with their 3D counterparts. The typical 2D perovskites can be obtained by cutting 3D perovskites along  < 100 >  orientation by incorporation of bulky organic spacers, which play a key role in the performance of 2D perovskite solar cells (PSCs). Compared with aliphatic spacers, aromatic spacers with high dielectric constant have the potential to decrease the dielectric and quantum confinement effect of 2D perovskites, promote efficient charge transport and reduce the exciton binding energy, all of which are beneficial for the photovoltaic performance of 2D PSCs. In this review, we aim to provide useful guidelines for the design of aromatic spacers for 2D perovskites. We systematically reviewed the recent progress of aromatic spacers used in 2D PSCs. Finally, we propose the possible design strategies for aromatic spacers that may lead to more efficient and stable 2D PSCs.

Ferroelectric Wide-Bandgap Metal Halide Perovskite Field-Effect Transistors: Toward Transparent Electronics

Transparent field-effect transistors (FETs) are attacking intensive interest for constructing fancy "invisible" electronic products. Presently, the main technology for realizing transparent FETs is based on metal oxide semiconductors, which have wide-bandgap but generally demand sputtering technique or high-temperature (>350 °C) solution process for fabrication. Herein, a general device fabrication strategy for metal halide perovskite (MHP) FETs is shown, by which transparent perovskite FETs are successfully obtained using low-temperature (<150 °C) solution process. This strategy involves the employment of ferroelectric copolymer poly(vinylidene fluoride-co-trifluoroethylene) (PVDF-TrFE) as the dielectric, which conquers the challenging issue of gate-electric-field screening effect in MHP FETs. Additionally, an ultra-thin SnO₂ is inserted between the source/drain electrodes and MHPs to facilitate electron injection. Consequently, n-type semi-transparent MAPbBr₃ FETs and fully transparent MAPbCl₃ FETs which can operate well at room temperature with mobility over 10^-3  cm²  V^-1  s^-1 and on/off ratio >10³ are achieved for the first time. The low-temperature solution processability of these FETs makes them particularly attractive for applications in low-cost, large-area transparent electronics.

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.

Polarization-Tunable Perovskite Light-Emitting Metatransistor

Emerging immersive visual communication technologies require light sources with complex functionality for dynamic control of polarization, directivity, wavefront, spectrum, and intensity of light. Currently, this is mostly achieved by free space bulk optic elements, limiting the adoption of these technologies. Flat optics based on artificially structured metasurfaces that operate at the sub-wavelength scale are a viable solution, however, their integration into electrically driven devices remains challenging. Here, a radically new approach to monolithic integration of a dielectric metasurface into a perovskite light-emitting transistor is demonstrated. It is shown that nanogratings directly structured on top of the transistor channel yield an 8-fold increase of electroluminescence intensity and dynamic tunability of polarization. This new light-emitting metatransistor device concept opens unlimited opportunities for light management strategies based on metasurface design and integration.

Theoretical study on ferroelectric nitrides with super-wurtzite structures for solar energy conversion applications

Polarized structured nitride semiconductors are attractive due to their unique and environment-friendly electronic properties. The stability, ferroelectricity and photocatalytic and photovoltaic properties of super-wurtzite Mg₂XN₃ (X = Bi, Mo, Nb, Sb, Ta, Tc and W) were determined based on first principles calculations in this study. The calculated results indicate that Mg₂XN₃ (X = Sb, Ta, Bi and Nb) are stable polar nitrides by phonon frequencies, elastic coefficients and ferroelectric analysis. Mg₂XN₃ (X = Sb, Ta and Nb) with large ferroelectric polarization strength could absorb ultraviolet light to promote photocatalytic water splitting for hydrogen production. Mg₂BiN₃ is a new excellent photovoltaic candidate due to its ideal energy band, high electron mobility, high absorption coefficient and large ferroelectric polarization strength.

A Review of Perovskite-Based Photodetectors and Their Applications

Perovskite photodetectors have attracted much research and attention because of their outstanding photoelectric characteristics, such as good light harvesting capability, excellent carrier migration behavior, tunable band gap, and so on. Recently, the reported studies mainly focus on materials synthesis, device structure design, interface engineering and physical mechanism analysis to improve the device characteristics, including stability, sensitivity, response speed, device noise, etc. This paper systematically summarizes the application fields and device structures of several perovskite photodetectors, including perovskite photoconductors, perovskite photodiodes, and perovskite phototransistors. Moreover, based on their molecular structure, 3D, 2D, 1D, and 0D perovskite photodetectors are introduced in detail. The research achievements and applications of perovskite photodetectors are summarized. Eventually, the future research directions and main challenges of perovskite photodetectors are prospected, and some possible solutions are proposed. The aim of the work is to provide a new thinking direction for further improving the performance of perovskite photodetectors.

Stable and efficient soft perovskite crystalline film based solar cells prepared with a facile encapsulation method

The quasi Fermi level for electrons in a soft perovskite crystalline thin film and the contact qualities at the PCBM/perovskite and perovskite/P3CT-Na interfaces can be increased using a facile encapsulation method, which improves the device performance and stability of the resultant perovskite solar cells. In the encapsulated perovskite solar cells, the averaged open-circuit voltage (V_OC) largely increases from 0.981 V to 1.090 V after 9 days mainly due to the increased quasi Fermi levels. Besides, the reflectance and photoluminescence (PL) spectra show improved contact qualities at the PCBM/perovskite and perovskite/P3CT-Na interfaces, which can be used to explain the increase in the short-circuit current density (J_SC) from 21.68 mA cm^-2 to 23.48 mA cm^-2 after the encapsulation process. Besides, nanosecond time-resolved PL and temperature-dependent PL spectra can be used to explain the increased V_OC, which is mainly due to the increased shallow defect density and thereby increasing the exciton binding energy of the encapsulated perovskite sample. It is noted that the averaged power conversion efficiency (PCE) slowly decreases from 18.24% to 16.52% within 45 days.

Metal Halide Perovskite/Electrode Contacts in Charge-Transporting-Layer-Free Devices

Metal halide perovskites have drawn substantial interest in optoelectronic devices in the past decade. Perovskite/electrode contacts are crucial for constructing high-performance charge-transporting-layer-free perovskite devices, such as solar cells, field-effect transistors, artificial synapses, memories, etc. Many studies have evidenced that the perovskite layer can directly contact the electrodes, showing abundant physicochemical, electronic, and photoelectric properties in charge-transporting-layer-free perovskite devices. Meanwhile, for perovskite/metal contacts, some critical interfacial physical and chemical processes are reported, including band bending, interface dipoles, metal halogenation, and perovskite decomposition induced by metal electrodes. Thus, a systematic summary of the role of metal halide perovskite/electrode contacts on device performance is essential. This review summarizes and discusses charge carrier dynamics, electronic band engineering, electrode corrosion, electrochemical metallization and dissolution, perovskite decomposition, and interface engineering in perovskite/electrode contacts-based electronic devices for a comprehensive understanding of the contacts. The physicochemical, electronic, and morphological properties of various perovskite/electrode contacts, as well as relevant engineering techniques, are presented. Finally, the current challenges are analyzed, and appropriate recommendations are put forward. It can be expected that further research will lead to significant breakthroughs in their application and promote reforms and innovations in future solid-state physics and materials science.

A general one-step plug-and-probe approach to top-gated transistors for rapidly probing delicate electronic materials

The miniaturization of silicon-based electronics has motivated considerable efforts in exploring new electronic materials, including two-dimensional semiconductors and halide perovskites, which are usually too delicate to maintain their intrinsic properties during the harsh device fabrication steps. Here we report a convenient plug-and-probe approach for one-step simultaneous van der Waals integration of high-k dielectrics and contacts to enable top-gated transistors with atomically clean and electronically sharp dielectric and contact interfaces. By applying the plug-and-probe top-gate transistor stacks on two-dimensional semiconductors, we demonstrate an ideal subthreshold swing of 60 mV per decade. Using this approach on delicate lead halide perovskite, we realize a high-k top-gate CsPbBr₃ transistor with a low operating voltage and a very high two-terminal field-effect mobility of 32 cm² V^-1 s^-1. This approach can be extended to centimetre-scale MoS₂ and perovskite and generate top-gated transistor arrays, offering a rapid and convenient way of accessing intrinsic properties of delicate emerging materials.

Grain engineering for improved charge carrier transport in two-dimensional lead-free perovskite field-effect transistors

Controlling crystal growth and reducing the number of grain boundaries are crucial to maximize the charge carrier transport in organic-inorganic perovskite field-effect transistors (FETs). Herein, the crystallization and growth kinetics of a Sn(II)-based 2D perovskite, using 2-thiopheneethylammonium (TEA) as the organic cation spacer, were effectively regulated by the hot-casting method. With increasing crystalline grain size, the local charge carrier mobility is found to increase moderately from 13 cm² V^-1 s^-1 to 16 cm² V^-1 s^-1, as inferred from terahertz (THz) spectroscopy. In contrast, the FET operation parameters, including mobility, threshold voltage, hysteresis, and subthreshold swing, improve substantially with larger grain size. The optimized 2D (TEA)₂SnI₄ transistor exhibits hole mobility of up to 0.34 cm² V^-1 s^-1 at 295 K and a higher value of 1.8 cm² V^-1 s^-1 at 100 K. Our work provides an important insight into the grain engineering of 2D perovskites for high-performance FETs.

Intensity modulated photocurrent spectroscopy to investigate hidden kinetics at hybrid perovskite–electrolyte interface

The numerous assorted accounts of the fundamental questions of ion migration in hybrid perovskites are making the picture further intricate. The review of photo-induced ion migration using small perturbation frequency domain techniques other than impedance spectroscopy is more crucial now. Herein, we probe into this by investigating perovskite–electrolyte (Pe–E) and polymer-aqueous electrolyte (Po–aqE) interface using intensity modulated photocurrent spectroscopy (IMPS) in addition to photoelectrochemical impedance spectroscopy (PEIS). We reported that the electronic-ionic interaction in hybrid perovskites including the low-frequency ion/charge transfer and recombination kinetics at the interface leads to the spiral feature in IMPS Nyquist plot of perovskite-based devices. This spiral trajectory for the perovskite-electrolyte interface depicts three distinct ion kinetics going on at the different time scales which can be more easily unveiled by IMPS rather than PEIS. Hence, IMPS is a promising alternative to PEIS. We used Peter’s method of interpretation of IMPS plot in photoelectrochemistry to estimate charge transfer efficiency \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$({Q}_{ste})$$\end{document}(Qste) from the Rate Constant Model. The \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${Q}_{ste}$$\end{document}Qste at low-frequency for Pe–E interface exceeds unity due to ion migration induced modified potential across the perovskite active layer. Hence, ion migration and mixed electronic-ionic conductivity of hybrid perovskites are responsible for the extraordinary properties of this material.

Doping Mn2+in hybrid Ruddlesden-Popper phase of layered double perovskite (BA)4AgBiBr8

The layered hybrid double perovskites emerged as excellent semiconductor materials owing to their environment compatibility and stability. However, these materials are weakly luminescent, and their photoluminescence (PL) properties can be modulated via doping. While Mn²⁺doping in perovskites is well known, but to the best of our knowledge the doping of Mn²⁺in layered double perovskites (LDPs) is yet to be explored. Herein, for the first time, we demonstrate the doping of Mn²⁺in hybrid inorganic-organic two-dimensional (2D) LDPs, (BA)₄AgBiBr₈(BA = n-butyl amine) via a simple solid-state mechanochemical route. The powder x-ray diffraction pattern, and electron paramagnetic resonance analysis confirm the successful incorporation of Mn²⁺ions inside (BA)₄AgBiBr₈lattice. The Mn²⁺doped 2D LDP shows energy transfer from host excitons to d-electrons of Mn²⁺ions, which results in red-shifted broad Mn²⁺emission band centered at 625 nm, attributed to thespin-forbidden⁴T₁to⁶A₁internal transition. This work opens up new possibilities to dope metal ions in 2D LDPs to tune the optical as well as magnetic properties.

Review on Perovskite Semiconductor Field-Effect Transistors and Their Applications

Perovskite materials are considered as the most alluring successor to the conventional semiconductor materials to fabricate solar cells, light emitting diodes and electronic displays. However, the use of the perovskite semiconductors as a channel material in field effect transistors (FET) are much lower than expected due to the poor performance of the devices. Despite low attention, the perovskite FETs are used in widespread applications on account of their unique opto-electrical properties. This review focuses on the previous works on perovskite FETs which are summarized into tables based on their structures and electrical properties. Further, this review focuses on the applications of perovskite FETs in photodetectors, phototransistors, light emitting FETs and memory devices. Moreover, this review highlights the challenges faced by the perovskite FETs to meet the current standards along with the future directions of these FETs. Overall, the review summarizes all the available information on existing perovskite FET works and their applications reported so far.

Thermally-induced drift of A-site cations at solid-solid interface in physically paired lead halide perovskites

The promise of hybrid organic-inorganic halide perovskite solar cells rests on their exceptional power conversion efficiency routinely exceeding 25% in laboratory scale devices. While the migration of halide ions in perovskite thin films has been extensively investigated, the understanding of cation diffusion remains elusive. In this study, a thermal migration of A‑site cations at the solid-solid interface, formed by two physically paired MAPbI₃ and FAPbI₃ perovskite thin films casted on FTO, is demonstrated through continuous annealing at comparably low temperature (100 °C). Diffusion of methylammonium (CH₃NH₃⁺, MA⁺) cations into the low‑symmetry yellow δ‑FAPbI₃ phase triggers a transition from the yellow (δ) to black (α) phase evident in the distinctive color change and verified by shifts in absorption bands and X‑ray diffraction patterns. Intermixing of the A‑site cations MA⁺ and FA⁺ (CH(NH₂)₂⁺) occurred for both systems, α‑MAPbI₃/δ‑FAPbI₃ and α‑MAPbI₃/α‑FAPbI₃. The structural and compositional changes in both cases support a thermally activated ion drift unambiguously demonstrated through changes in the absorption and X-ray photoelectron spectra. Moreover, the physical contact annealing (PCA) leads to healing of defects and pinholes in α‑MAPbI₃ thin films, which was correlated to longer recombination lifetimes in mixed MA_xFA_1-xPbI₃ thin films obtained after PCA and probed by ultrafast transient absorption spectroscopy.

High-Throughput Evaluation of Emission and Structure in Reduced-Dimensional Perovskites

High-throughput experimentation (HTE) seeks to accelerate the exploration of materials space by uniting robotics, combinatorial methods, and parallel processing. HTE is particularly relevant to metal halide perovskites (MHPs), a diverse class of optoelectronic materials with a large chemical space. Here we develop an HTE workflow to synthesize and characterize light-emitting MHP single crystals, allowing us to generate the first reported data set of experimentally derived photoluminescence spectra for low-dimensional MHPs. We leverage the accelerated workflow to optimize the synthesis and emission of a new MHP, methoxy-phenethylammonium lead iodide ((4-MeO-PEAI)₂-PbI₂). We then synthesize 16 000 MHP single crystals and measure their photoluminescence to study the effects of synthesis parameters and compositional engineering on the emission intensity of 54 distinct MHPs: we achieve an acceleration factor of more than 100 times over previously reported HTE MHP synthesis and characterization methods. Using insights derived from this analysis, we screen an existing database for new, potentially emissive MHPs. On the basis of the Tanimoto similarity of the bright available emitters, we present our top candidates for future exploration. As a proof of concept, we use one of these (3,4-difluorophenylmethanamine) to synthesize an MHP which we find has a photoluminescence quantum yield of 10%.

Electrode Engineering in Halide Perovskite Electronics: Plenty of Room at the Interfaces

Contact engineering is a prerequisite for achieving desirable functionality and performance of semiconductor electronics, which is particularly critical for organic-inorganic hybrid halide perovskites due to their ionic nature and highly reactive interfaces. Although the interfaces between perovskites and charge-transporting layers have attracted lots of attention due to the photovoltaic and light-emitting diode applications, achieving reliable perovskite/electrode contacts for electronic devices, such as transistors and memories, remains as a bottleneck. Herein, a critical review on the elusive nature of perovskite/electrode interfaces with a focus on the interfacial electrochemistry effects is presented. The basic guidelines of electrode selection are given for establishing non-polarized interfaces and optimal energy level alignment for perovskite materials. Furthermore, state-of-the-art strategies on interface-related electrode engineering are reviewed and discussed, which aim at achieving ohmic transport and eliminating hysteresis in perovskite devices. The role and multiple functionalities of self-assembled monolayers that offer a unique approach toward improving perovskite/electrode contacts are also discussed. The insights on electrode engineering pave the way to advancing stable and reliable perovskite devices in diverse electronic applications.

Doping of Sn-based two-dimensional perovskite semiconductor for high-performance field-effect transistors and thermoelectric devices

Doping is an important technique for semiconductor materials and devices, yet effective and controllable doping of organic-inorganic halide perovskites is still a challenge. Here, we demonstrate a facile way to dope two-dimensional Sn-based perovskite (PEA)2SnI4 by incorporating SnI4 in the precursor solutions. It is observed that Sn4+ produces p-doping effect on the perovskite, which increases the electrical conductivity by 105 times. The dopant SnI4 is also found to improve the film morphology of (PEA)2SnI4, leading to reduced trap states. This doping technique allows us to improve the room temperature mobility of (PEA)2SnI4 field-effect transistors from 0.25 to 0.68 cm2 V-1 s-1 thanks to reduced trapping effects in the doped devices. Moreover, the doping technique enables the characterization and improvement of the thermoelectric performance of (PEA)2SnI4 films, which show a high power factor of 3.92 μW m-1 K-2 at doping ratio of 5 mol %.

Greatly improved photoresponse in the MAPbBr3/Si heterojunction by introducing an ITO layer and optimizing MAPbBr3 layer thickness

In this paper, a CH₃NH₃(MA)PbBr₃/Si heterojunction photodetector (PD) is prepared, and a simple method is proposed to improve the performance by introducing an ITO conductive layer and modulating thickness of the MAPbBr₃ layer. The results indicate that the MAPbBr₃/Si heterojunction PD exhibits an ultra-broadband photoresponse ranging from 405 to 1064 nm, and excellent performances with the responsivity (R) of 0.394 mA/W, detectivity (D) of 0.11×10¹⁰ Jones, and response times of ∼2176/∼257 ms. When adding the ITO layer, the R and D are greatly improved to 0.426 A/W and 5.17×10¹⁰ Jones, which gets an increment of 1.08×10⁵% and 4.7×10³%, respectively. Meanwhile, the response times are reduced to ∼130/∼125 ms, and a good environmental stability is obtained. Moreover, it is found that the photoresponse is strongly dependent on the thickness of the MAPbBr₃ layer. By modulating the MAPbBr₃ layer thickness from ∼85 to ∼590 nm, the performances are further improved with the best R of ∼0.87 A/W, D of ∼1.92×10¹¹ Jones, and response times of ∼129/∼130 ms achieved in the ∼215 nm-thick PD.

Air processed Cs2AgBiBr6 lead-free double perovskite high-mobility thin-film field-effect transistors

This study focuses on the fabrication and characterization of Cs2AgBiBr6 double perovskite thin film for field-effect transistor (FET) applications. The Cs2AgBiBr6 thin films were fabricated using a solution process technique and the observed XRD patterns demonstrate no diffraction peaks of secondary phases, which confirm the phase-pure crystalline nature. The average grain sizes of the spin-deposited film were also calculated by analysing the statistics of grain size in the SEM image and was found to be around 412 (± 44) nm, and larger grain size was also confirmed by the XRD measurements. FETs with different channel lengths of Cs2AgBiBr6 thin films were fabricated, under ambient conditions, on heavily doped p-type Si substrate with a 300 nm thermally grown SiO2 dielectric. The fabricated Cs2AgBiBr6 FETs showed a p-type nature with a positive threshold voltage. The on-current, threshold voltage and hole-mobility of the FETs decreased with increasing channel length. A high average hole mobility of 0.29 cm2 s-1 V-1 was obtained for the FETs with a channel length of 30 µm, and the hole-mobility was reduced by an order of magnitude (0.012 cm2 s-1 V-1) when the channel length was doubled. The on-current and hole-mobility of Cs2AgBiBr6 FETs followed a power fit, which confirmed the dominance of channel length in electrostatic gating in Cs2AgBiBr6 FETs. A very high-hole mobility observed in FET could be attributed to the much larger grain size of the Cs2AgBiBr6 film made in this work.

Single Crystal Halide Perovskite Film for Nonlinear Resistive Memory with Ultrahigh Switching Ratio

Morre's law is coming to an end only if the memory industry can keep stuffing the devices with new functionality. Halide perovskite acts as a promising candidate for application in next-generation nonvolatile memory. As is well known, the switching ratio is the key device requirement of resistive memory to improve recognition accuracy. Here, the authors introduce an all-inorganic halide perovskite CsPbBr₃ single crystal film (SCF) into resistive memory as an active layer. The Ag/CsPbBr₃ /Ag memory cells exhibit reproducible resistive switching with an ultrahigh switching ratio (over 10⁹ ) and a fast switching speed (1.8 µs). It is studied that the Schottky barrier of metal/CsPbBr₃ SCF contact follows the tendency of Schottky-Mott theory, and the Fermi level pinning effect is effectively reduced. The interface S parameter of metal/CsPbBr₃ SCF contact is 0.50, suggesting a great interface contact is formed. The great interface contact contributes to the steady high resistance state (HRS), and then the steady HRS leads to an ultrahigh resistive switching ratio. This work demonstrates high performance from halide perovskite SCF-based memory. The introduction of halide perovskite SCF in resistive random access memory provides great potential as an alternative in future computing systems.

First-Principles Molecular Dynamics in Metal-Halide Perovskites: Contrasting Generalized Gradient Approximation and Hybrid Functionals

First-principles molecular dynamics (FPMD) represents a valuable tool to probe dynamical properties of metal-halide perovskites (MHPs) which are key to their success in optoelectronic devices. Most FPMD studies rely on generalized gradient approximation (GGA) functionals for computational efficiency matters, while hybrid functionals, although computationally demanding, are usually needed to accurately describe structural and electronic properties of MHPs. This Letter reports FPMD simulations on CsPbI₃ based on the hybrid PBE0 functional. Our results demonstrate that PBE0 leads to lattice parameters and phonon modes in excellent agreement with experimental data, while GGA results overestimate the lattice parameter and the electronic band gap and underestimate the phonon energies. Our FPMD results also shed light on anharmonic effects and double-well instabilities in the octahedral tilting, highlighting a lowered free energy barrier for PBE0 and farther separated potential wells. Our results suggest that hybrid functionals are required to accurately describe crystal structure, lattice dynamics, and anharmonicity in MHPs.

Moisture Stability of Perovskite Solar Cells Processed in Supercritical Carbon Dioxide

Performance degradation under environmental conditions currently limits the practical utility of perovskite-based solar cells. The moisture stability of CH3NH3PbI3 perovskite films and solar cells was measured during exposure to three different levels of relative humidity. The films were crystallized at two different temperatures with and without simultaneous exposure to supercritical carbon dioxide. The film crystallinity, optical absorption, and device photoconversion efficiency was measured over time for three relative humidity levels and both crystallization methods. It was determined that film crystallization in supercritical CO2 resulted in significant improvement in moisture stability for films processed at 50 °C, but negligible improvement in stability for films processed at 100 °C.

Proton irradiation effects on mechanochemically synthesized and flash-evaporated hybrid organic-inorganic lead halide perovskites

A hybrid organic-inorganic halide perovskite is a promising material for developing efficient solar cell devices, with potential applications in space science. In this study, we synthesized methylammonium lead iodide (MAPbI₃) perovskites via two methods: mechanochemical synthesis and flash evaporation. We irradiated these perovskites with highly energetic 10 MeV proton-beam doses of 10¹¹, 10¹², 10¹³, and 4 × 10¹³protons cm^-2and examined the proton irradiation effects on the physical properties of MAPbI₃perovskites. The physical properties of the mechanochemically synthesized MAPbI₃perovskites were not considerably affected after proton irradiation. However, the flash-evaporated MAPbI₃perovskites showed a new peak in x-ray diffraction and an increased fluorescence lifetime in time-resolved photoluminescence under high-dose conditions, indicating considerable changes in their physical properties. This difference in behavior between MAPbI₃perovskites synthesized via the abovementioned two methods may be attributed to differences in radiation hardness associated with the bonding strength of the constituents, particularly Pb-I bonds. Our study will help to understand the radiation effect of proton beams on organometallic halide perovskite materials.

Printed Memtransistor Utilizing a Hybrid Perovskite/Organic Heterojunction Channel

Neuromorphic computing has the potential to address the inherent limitations of conventional integrated circuit technology, ranging from perception, pattern recognition, to memory and decision-making ( Acc. Chem. Res. 2019, 52 (4), 964-974) ( Nature 2004, 431 (7010), 796-803) ( Nat. Nanotechnol. 2013, 8 (1), 13-24). Despite their low power consumption ( Nano Lett. 2016, 16 (11), 6724-6732), traditional two-terminal memristors can perform only a single function while lacking heterosynaptic plasticity ( Nanotechnology 2013, 24 (38), 382001). Inspired by the unconditioned reflex, multiterminal memristive transistors (memtransistor) were developed to realize complex functions, such as multiterminal modulation and heterosynaptic plasticity ( Nature 2018, 554, (7693), 500-504). Here we combine a hybrid metal halide perovskite with an organic conjugated polymer to form heterojunction transistors that are responsive to both electrical and optical stimuli. We show that the synergistic effects of photoinduced ion migration in the perovskite and electronic transport in the polymer layers can be exploited to realize memristive functions. The device combines reversible, nonvolatile conductance modulation with large switching current ratios, high endurance, and long retention times. Using in situ scanning Kelvin probe microscopy and variable-temperature charge transport measurement, we correlate the collective effects of bias-induced and photoinduced ion migration with the heterosynaptic behavior observed in this hybrid memtransistor. The hybrid heterojunction channel concept is expected to be applicable to other material combinations making it a promising platform for deployment in innovative neuromorphic devices of the future.

Time-Dependent Field Effect in Three-Dimensional Lead-Halide Perovskite Semiconductor Thin Films

Charge transport in three-dimensional metal-halide perovskite semiconductors is due to a complex combination of ionic and electronic contributions, and its study is particularly relevant in light of their successful applications in photovoltaics as well as other opto- and microelectronic applications. Interestingly, the observation of field effect at room temperature in transistors based on solution-processed, polycrystalline, three-dimensional perovskite thin films has been elusive. In this work, we study the time-dependent electrical characteristics of field-effect transistors based on the model methylammonium lead iodide semiconductor and observe the drastic variations in output current, and therefore of apparent charge carrier mobility, as a function of the applied gate pulse duration. We infer this behavior to the accumulation of ions at the grain boundaries, which hamper the transport of carriers across the FET channel. This study reveals the dynamic nature of the field effect in solution-processed metal-halide perovskites and offers an investigation methodology useful to characterize charge carrier transport in such emerging semiconductors.

Emerging perovskite monolayers

The library of two-dimensional (2D) materials has been enriched over recent years with novel crystal architectures endowed with diverse exciting functionalities. Bulk perovskites, including metal-halide and oxide systems, provide access to a myriad of properties through molecular engineering. Their tunable electronic structure offers remarkable features from long carrier-diffusion lengths and high absorption coefficients in metal-halide perovskites to high-temperature superconductivity, magnetoresistance and ferroelectricity in oxide perovskites. Emboldened by the 2D materials research, perovskites down to the monolayer limit have recently emerged. Like other 2D species, perovskites with reduced dimensionality are expected to exhibit new physics and to herald next-generation multifunctional devices. In this Review, we critically assess the preliminary studies on the synthetic routes and inherent properties of monolayer perovskite materials. We also discuss how to exploit them for widespread applications and provide an outlook on the challenges and opportunities that lie ahead for this enticing class of 2D materials.

Advances of Nonlinear Photonics in Low-Dimensional Halide Perovskites

Hybrid halide perovskites emerging as a highly promising class of functional materials for semiconductor optoelectronic applications have drawn great attention from worldwide researchers. In the past few years, prominent nonlinear optical properties have been demonstrated in perovskite bulk structures indicating their bright prospect in the field of nonlinear optics (NLO). Following the surge of 3D perovskites, more recently, the low-dimensional perovskites (LDPs) materials ranging from two-, one-, to zero-dimension such as quantum-wells or colloidal nanostructures have displayed unexpectedly attractive NLO response due to the strong quantum confinement, remarkable exciton effect, and structural diversity. In this perspective, the current state of the art is reviewed in the field of NLO for LDP materials. The relationship between confinement effect and NLO is analyzed systematically to give a comprehensive understanding of the function of dimension reduction. Furthermore, future directions and challenges toward the improvement of the NLO in LDP materials are discussed to provide an outlook in this rapidly developing field.

Room-Temperature Halide Perovskite Field-Effect Transistors by Ion Transport Mitigation

Solution-processed halide perovskites have emerged as excellent optoelectronic materials for applications in photovoltaic solar cells and light-emitting diodes. However, the presence of mobile ions in the material hinders the development of perovskite field-effect transistors (FETs) due to screening of the gate potential in the nearby perovskite channel, and the resulting impediment to achieving gate modulation of an electronic current at room temperature. Here, room-temperature operation is demonstrated in cesium lead tribromide (CsPbBr3 ) perovskite-based FETs using an auxiliary ferroelectric gate of poly(vinylidenefluoride-co-trifluoroethylene) [P(VDF-TrFE)], to electrostatically fixate the mobile ions. The large interfacial polarization of the ferroelectric gate attracts the mobile ions away from the main nonferroelectric gate interface, thereby enabling modulation of the electronic current through the channel by the main gate. This strategy allows for realization of the p-type CsPbBr3 channel and revealing the thermally activated nature of the hole charge transport. The proposed strategy is generic and can be applied for regulating ions in a variety of ionic-electronic mixed semiconductors.

Ligand-Driven Grain Engineering of High Mobility Two-Dimensional Perovskite Thin-Film Transistors

Controlling grain growth is of great importance in maximizing the charge carrier transport for polycrystalline thin-film electronic devices. The thin-film growth of halide perovskite materials has been manipulated via a number of approaches including solvent engineering, composition engineering, and post-treatment processes. However, none of these methods lead to large-scale atomically flat thin films with extremely large grain size and high charge carrier mobility. Here, we demonstrate a novel π-conjugated ligand design approach for controlling the thin-film nucleation and growth kinetics in two-dimensional (2D) halide perovskites. By extending the π-conjugation and increasing the planarity of the semiconducting ligand, nucleation density can be decreased by more than 5 orders of magnitude. As a result, wafer-scale 2D perovskite thin films with highly ordered crystalline structures and extremely large grain size are readily obtained. We demonstrate high-performance field-effect transistors with hole mobility approaching 10 cm² V^-1 s^-1 with ON/OFF current ratios of ∼10⁶ and excellent stability and reproducibility. Our modeling analysis further confirms the origin of enhanced charge transport and field and temperature dependence of the observed mobility, which allows for clear deciphering of the structure-property relationships in these nascent 2D semiconductor systems.

Superior photo-carrier diffusion dynamics in organic-inorganic hybrid perovskites revealed by spatiotemporal conductivity imaging

The outstanding performance of organic-inorganic metal trihalide solar cells benefits from the exceptional photo-physical properties of both electrons and holes in the material. Here, we directly probe the free-carrier dynamics in Cs-doped FAPbI₃ thin films by spatiotemporal photoconductivity imaging. Using charge transport layers to selectively quench one type of carriers, we show that the two relaxation times on the order of 1 μs and 10 μs correspond to the lifetimes of electrons and holes in FACsPbI₃, respectively. Strikingly, the diffusion mapping indicates that the difference in electron/hole lifetimes is largely compensated by their disparate mobility. Consequently, the long diffusion lengths (3~5 μm) of both carriers are comparable to each other, a feature closely related to the unique charge trapping and de-trapping processes in hybrid trihalide perovskites. Our results unveil the origin of superior diffusion dynamics in this material, crucially important for solar-cell applications.

Mobile ions determine the luminescence yield of perovskite light-emitting diodes under pulsed operation

The external quantum efficiency of perovskite light-emitting diodes (PeLEDs) has advanced quickly during the past few years. However, under pulsed operation, an operation mode which is important for display and visible light communication, the performance of PeLEDs changes a lot and requires in-depth understanding to facilitate these applications. Here, we report the response of PeLEDs under pulsed operation in the range of 10 Hz to 20 kHz. Beyond transient effects in the low frequencies, we find that for higher frequencies (>500 Hz) the transient electroluminescence intensity depends strongly on the duty cycle. This feature is much more pronounced and of different origin than that in conventional LEDs. We rationalise our experimental observations using a mathematical model and assign these features to the effect of mobile ionic charges in the perovskite. Our work also provides important implications for the operation of PeLEDs under the steady state, where accumulation of mobile ions at the interfaces could be beneficial for high electroluminescence yields but harmful for the long-term stability.

Solution Epitaxy of Halide Perovskite Thin Single Crystals for Stable Transistors

Halide perovskites hold promise for energy and optoelectronic applications due to their fascinating photophysical properties and facile processing. Among various forms, epitaxial thin single crystals (TSCs) are highly desirable due to their high crystallinity, reduced defects, and easy epitaxial integration with other materials. However, a cost-effective method for obtaining TSCs with perfect epitaxial features remains elusive. Here, we demonstrate a direct epitaxial growth of high-quality all-inorganic perovskite CsPbBr₃ TSCs on various substrates through a facile solution process under near-ambient conditions. Structural characterizations reveal a high-quality epitaxy between the obtained perovskite TSCs and substrates, thus leading to efficiently reduced defects. The resultant TSCs display a low trap density (∼10¹¹ cm^-3) and a long carrier lifetime (∼10.16 ns). Top-gate/top-contact transistors based on these TSCs exhibit high on/off ratios of over 10⁵, an optimal hole mobility of 3.9 cm² V^-1 s^-1, almost hysteresis-free operation, and high stability at room temperature. Such a facile approach for the high-yield production of perovskite epitaxial TSCs will enable a broad range of high-performance electronic applications.

Asymmetric Bipolar Resistive Switching of Halide Perovskite Film in Contact with TiO2 Layer

Halide perovskite materials such as methylammonium lead iodide (CH₃NH₃PbI₃) have attracted considerable interest for the resistive random-access memory applications, which exploit a dramatic change in the resistance by an external electric bias. In many semiconductor films, the drift, accumulation, and chain formation of defects explain the change in the resistance by an external bias. This study demonstrates that the interface of CH₃NH₃PbI₃ with TiO₂ has a significant impact on the formation and rupture of defect chains and causes the asymmetric bipolar resistive switching in the Au/CH₃NH₃PbI₃/TiO₂/FTO device (FTO = fluorine-doped tin oxide). When a negative bias is applied to the Au electrode, iodine interstitials with the lowest migration activation energy move toward TiO₂ in the CH₃NH₃PbI₃ layer and pile up at the CH₃NH₃PbI₃-TiO₂ interface. Under the same condition, oxygen vacancies in the TiO₂ layer also travel to the CH₃NH₃PbI₃-TiO₂ interface and strongly attract iodine interstitials. As a result, a Schottky barrier appears at the CH₃NH₃PbI₃-TiO₂ interface, and the resistance of Au/CH₃NH₃PbI₃/TiO₂/FTO becomes much larger than that of Au/CH₃NH₃PbI₃/FTO in the high resistance state. The frequency dependence of the capacitance confirms the asymmetric appearance of a large space charge polarization at the CH₃NH₃PbI₃-TiO₂ interface, which causes the unique bipolar resistive switching behavior with the on/off ratio (10³) and retention time (>10⁴ seconds) at -0.85 V in Au/CH₃NH₃PbI₃/TiO₂/FTO film.

Variational hysteresis and photoresponse behavior of MAPbX3(X= I, Br, Cl) perovskite single crystals

High-quality MAPbX₃(X= I, Br, Cl) single crystals with a desirable size were grown through an inverse temperature crystallization method. Systematically measurements of current-voltage (I-V) hysteresis show that the hysteresis is strongly dependent on the measuring protocol, including scan rate and light illumination condition, which reveals the competition of three main factors that influence the charge dynamics in different regimes, defect trap, MA⁺dipoles rotation, and ion migration. In the dark, defect trapping is the dominant charge transport dynamics at low bias in the MAPbI₃, while the MA⁺dipole rotation is significant in MAPbBr₃, and ion migration occurs in MAPbCl₃. However, as bias increases, MA⁺dipole rotation plays a crucial role in the conductivity either in the dark or under light illumination. The time-dependent photoresponse exhibits different tendencies under various biases. The slow rising dynamics of photoresponse in MAPbX₃is attributed to the slow rotation of MA⁺dipoles, while an immediate overshoot followed by a decay suggests significant ion migration contribution at high external bias. The results serve as comprehensive experimental support to understand the hysteresis behaviors and slow photoresponse in MAPbX₃, particularly in MAPbCl₃, and provide a guide for future work in MAPbX₃based optoelectronic devices.

Improved efficiency and air stability of two-dimensional p-i-n inverted perovskite solar cells by Cs doping

Two-dimensional perovskite solar cells (2-D PSCs) have attracted much research attention in recent years because they are more stable in a regular environment than three-dimensional (3-D) ones are. In this study, we doped Cs into 2D perovskite (BA2(MA)2Pb3I10) films as the absorbing layers of the 2-D p-i-n inverted PSCs to investigate the influence of the Cs doping concentration on the properties of the 2-D perovskite films and the fabricated solar cells. Cs doping clearly improves the power conversion efficiency (PCE) and air stability of the PSCs. Doping perovskite with 10% Cs (the best doping concentration in this study) can increase the PSC efficiency from 7.98% to 10.11%. Scanning electron microscopy indicates the improved surface quality and crystallinity by Cs doping. However, excess Cs doping degrades the PCE of the PSCs. Furthermore, 10% Cs doped PSCs show air stability superior to that of undoped ones in unpackaged humidity environments. After exposure to 55% relative humidity (RH) in 19 °C air for 300 h, the PCE of the PSC decreased by only 39%, in contrast to 84% for the undoped PSC.

Halide Perovskites: A New Era of Solution-Processed Electronics

Organic-inorganic mixed halide perovskites have emerged as an excellent class of materials with a unique combination of optoelectronic properties, suitable for a plethora of applications ranging from solar cells to light-emitting diodes and photoelectrochemical devices. Recent works have showcased hybrid perovskites for electronic applications through improvements in materials design, processing, and device stability. Herein, a comprehensive up-to-date review is presented on hybrid perovskite electronics with a focus on transistors and memories. These applications are supported by the fundamental material properties of hybrid perovskite semiconductors such as tunable bandgap, ambipolar charge transport, reasonable mobility, defect characteristics, and solution processability, which are highlighted first. Then, recent progresses on perovskite-based transistors are reviewed, covering aspects of fabrication process, patterning techniques, contact engineering, 2D versus 3D material selection, and device performance. Furthermore, applications of perovskites in nonvolatile memories and artificial synaptic devices are presented. The ambient instability of hybrid perovskites and the strategies to tackle this bottleneck are also discussed. Finally, an outlook and opportunities to develop perovskite-based electronics as a competitive and feasible technology are highlighted.