Perovskite-based Devices Research Articles

Idealizing Air-Processed Perovskite Film Competitive by Surface Lattice Etching-Reconstruction for High-Efficiency Solar Cells.

Air-processed perovskite solar cells are desirable for the large-scale manufacturing application in the future, yet the presence of moisture and oxygen goes against perovskite crystallization and deteriorates phase stabilization, leading to the formation of substantial defective nano-impurities, especially on the vulnerable surface. Here, we propose a strategy to simultaneously remove superficial defect layer and solidify the surface by soaking air-fabricated perovskite film into low-polar organic esters at elevated temperature to trigger an in-situ dynamic surface lattice disassemble and reconstruction process. Molecular dynamics simulations and experimental results indicate that the inorganic CsPbI2Br perovskite is first dissolved and then the Br-rich phase is recrystallized at solid-liquid interface owing to the balance between weak solubility and high-temperature induced annealing process, thus hardening the soft surface and releasing the lattice tensile stress, which benefits the minimization of interfacial recombination and improvement of the structural stability. As a result, we prepare a carbon-based CsPbI2Br device in complete air without precise control on humidity, achieving a champion efficiency of 15.37% with excellent resistance to harsh attackers. This method offers a promising avenue for overcoming the limit of processing conditions on advancing perovskite-based optoelectronic devices.

Melt Alloying of Two-Dimensional Hybrid Perovskites: Composition-Dependence of Thermal and Optical Properties.

Melt alloying, the process of melting a physical powder blend to create a homogeneous alloy, is widely used in materials processing. By carefully selecting the materials and their proportions, the physical properties of the resulting alloy can be precisely controlled. In this study, we investigate the possibility of utilizing melt alloying principles for meltable two-dimensional hybrid organic-inorganic perovskites (2D-HOIPs). We blend and melt mixtures of two selected 2D-HOIPs: the glass-forming (S-NEA)2PbBr4 (S-NEA = (S)-(-)-1-(1-naphthyl)ethylammonium) and the liquid-forming (1-MHA)2PbI4 (1-MHA = 1-methylhexylammonium). Upon melting and cooling, 1-MHA-poor blends (X1-MHA ≤ 50% mol, where X1-MHA corresponds to the relative molar concentration of (1-MHA)2PbI4 in the blend) form a hybrid glass, while 1-MHA-rich blends (X1-MHA ≥ 70% mol) crystallize. The melting temperature of all blends, as well as the glass transition temperature of the glass-forming blends, change according to blend composition. In all cases, melting produces a homogeneous structure, either glassy or crystalline, which remains such after the glassy samples are recrystallized upon a second heat treatment. This method enables band gap tuning of the blends, given that it varies with composition and crystallinity. Overall, this work demonstrates the applicability of classical melt processing to binary-component functional hybrid systems, and paves the way to solvent-free perovskite-based device fabrication.

Atomic Layer Deposition of ZnO on CsPbBr3 Perovskite Nanocrystals: Surface-Dependent Mechanistic Insights.

In this study, we investigate the atomic layer deposition (ALD) process on all-inorganic CsPbBr3 perovskite nanocrystals (PNCs) to introduce an inorganic electron transport layer (ETL) in light-emitting diode (LED) devices. Two types of CsPbBr3 PNCs were synthesized with oleate (OA) and oleylammonium (OLA) ligands on the surface. We found that CsPbBr3 PNCs with Cs oleate surfaces experienced severe photoluminescence (PL) quenching after the ALD process, while those with oleylammonium bromide surfaces did not show any significant PL drop. Transmission electron microscopy and X-ray photoelectron spectroscopy revealed that significant Pb metal formation and Ruddlesden-Popper planar faults, linked to uncoordinated Pb2+ ion defects, were generated in CsPbBr3 PNCs terminated with Cs oleate after ALD ZnO. Finally, we fabricated LEDs using PNCs with an ALD ZnO process to introduce inorganic ZnMgO nanoparticles as the ETL. The devices processed with ALD exhibited superior luminance and external quantum efficiency compared to those without the ALD process. This research provides crucial insights into the surface-dependent chemistry of PNCs and the surface-dependent performance of perovskite-based optoelectronic devices.

Ionic liquid additive induced holistic trap-passivation for enhanced charge transport in lead-halide perovskite-based transistors

Incorporating ionic liquid additives into perovskite-based electronic devices has been considerably demonstrated to improve device performance and stability via synergistic passivation effects. However, the advantages and understanding of ionic additives in perovskite field-effect transistors (FETs) have been explored far less. Herein, holistic trap-passivation is reported in a poly(3-hexylthiophene)-functionalized electrolyte-gated perovskite FETs with a solid-state ionic liquid (ss-IL) additive. The optimized ss-IL-incorporated methylammonium lead iodide (MAPbI3/ss-IL) FETs exhibited remarkable hole mobility of over 30 cm2 V−1 s−1 at an operating voltage of –1.5 V, attributed to suppressed lead/iodine vacancies and related traps and exhibiting excellent operational stability under ambient conditions with recoverable complex hysteresis behavior. These results demonstrate the promising synergistic impacts of the proposed trap engineering and provide a fundamental understanding of charge transport physics in doped perovskite semiconductors, essential for advancing their application as transistor-based devices.

Nonstoichiometry Promoted Solventless Recrystallization of a Thick and Compact CsPbBr3 Film for Real-Time Dynamic X-Ray Imaging.

Inorganic CsPbBr3 perovskite emerges as a promising material for the development of next-generation X-ray detectors. However, the formation of a high-quality thick film of CsPbBr3 has been challenging due to the low solubility of its precursor and its high melting point. To address this limitation, a nonstoichiometry approach is taken that allows lower-temperature crystallization of the target perovskite under the solventless condition. This approach capitalizes on the presence of excess volatile PbBr2 within the CsPbBr3 film, which induces melting point depression and promotes recrystallization of CsPbBr3 at a temperature much lower than its melting point concomitant with the escape of PbBr2. Consequently, thick and compact films of CsPbBr3 are formed with grains ten times larger than those in the pristine films. The resulting X-ray detector exhibits a remarkable sensitivity of 4.2 × 104 µC Gyair -1 cm-2 and a low detection limit of 136 nGyair s-1, along with exceptional operational stability. Notably, the CsPbBr3-based flat-panel detector achieves a high resolution of 0.65 lp pix-1 and the first demonstration of real-time dynamic X-ray imaging for perovskite-based devices.

Achieving vertical orientation films with superior environmental stability in quasi-2D lead iodide perovskites

The incorporation of a spacer cation to improve the stability of lead halide perovskites entails a trade-off, notably compromising film quality and device performance, particularly in quais-2D variants employing a higher proportion of hydrophobic, larger spacer cations. Addressing this challenge in quasi-2D perovskite-based devices requires enhancement in film morphology, crystallinity, and vertical orientation to optimize charge transport. Herein, we present a simple one step spin coating synthesis approach for producing PEA2MAn-1PbnI3n+1 (n = 5–2) thin films from a single precursor solution. Notably, our method operates at room temperature without the need of usually toxic anti-solvent or specialized additives, resulting in high quality crystalline films that are vertically oriented and smooth. We systematically investigate the impact of annealing processes on crystal structure, including gradient annealing (GA) as well as thermal annealing at 100℃ for durations of 10 and 15 minutes. Our findings indicate that the films with n = 4 exhibits superior crystallinity and vertical crystallographic orientation, alongside reduced roughness, and minimal contamination of the lower n mixtures. Gradient annealing notably enhances the crystallinity of n = 3 films. While the surface of all the films appears smooth with flake-like structure, the n = 2 sample notably exhibits pitting.

Fabrication Strategies for 2D Halide Perovskite Towards Next-Generation Optoelectronic Applications

AbstractHalide perovskites have emerged as promising materials in high-performance optoelectronics due to their exceptional optoelectrical properties, such as long carrier lifetime and tunable bandgap. Despite the promising capabilities of three-dimensional (3D) halide perovskites in applications like solar cells and light-emitting diodes, their operational stability remains a critical challenge. This review focuses on quasi-two-dimensional (2D) halide perovskites, which offer enhanced stability through their reduced dimensionality. We discuss the unique properties of these materials, including the ability to modify optical and electronic characteristics by altering the organic cations and the layer number in the perovskite structure. Additionally, we review various fabrication techniques, highlighting the shift from traditional low-temperature solution processes to more advanced solid, liquid, and vapor-phase methods, which address the limitations of conventional fabrication and enhance material quality. This comprehensive review aims to provide insights into the development of stable and efficient 2D halide perovskite-based optoelectronic devices, paving the way for their integration into next-generation optoelectronic applications.

Phase Distribution Dictates Charge Transfer and Transport Dynamics in Layered Quasi-2D Perovskite.

Strategic manipulation of spatiotemporal evolution of charge carriers is critical for optimizing performance of quasi-two-dimensional (2D) perovskite-based optoelectronic devices. Nonetheless, the inhomogeneous phase distribution and band alignment engender intricate energy landscapes, complicating internal charge and energy funneling processes. Herein, we integrate high spatiotemporal resolution transient absorption microscopy with multiple time-resolved spectroscopy and find that asynchronous electron and hole transfers rather than direct energy transfer govern the funneling mechanisms. Notably, the charge funneling pathways and transport behaviors can be modifiable by phase manipulation. The accumulation of small-n phases suppresses the electron funneling toward large-n phases and doubles the carrier diffusion rate from 0.085 to 0.20 cm2/s, yielding a 1.5-fold enhancement in diffusion length. Phase order engineering is further corroborated for facilitating charge separation. Our investigation underscores the prospects of manipulating the phase distribution to control internal charge funneling and transport, thereby substantiating the theoretical foundations for optimizing optoelectronic devices.

Diurnal Changes and Machine Learning Analysis of Perovskite Modules Based on Two Years of Outdoor Monitoring.

Long-term stability is the primary challenge for the commercialization of perovskite photovoltaics, exacerbated by limited outdoor data and unclear correlations between indoor and outdoor tests. In this study, we report on the outdoor stability testing of perovskite mini-modules conducted over a two-year period. We conducted a detailed analysis of the changes in performance across the day, quantifying both the diurnal degradation and the overnight recovery. Additionally, we employed the XGBoost regression model to forecast the power output. Our statistical analysis of extensive aging data showed that all perovskite configurations tested exhibited diurnal degradation and recovery, maintaining a linear relationship between these phases across all environmental conditions. Our predictive model, focusing on essential environmental parameters, accurately forecasted the power output of mini-modules with a 6.76% nRMSE, indicating its potential to predict the lifetime of perovskite-based devices.

Recent Advances in Perovskite-Based Flexible Electroluminescent Devices.

Perovskite-based flexible electroluminescent (EL) devices are emerging as promising candidates in the display field due to their exceptional optoelectronic properties and potential for cost-effective production. However, simultaneously achieving high EL performance, excellent flexibility and stretchability, robust mechanical strength, and diverse applications remains a significant challenge. In this review, we provide a comprehensive overview of the latest developments in perovskite-based flexible EL devices, covering both direct-current (DC) and alternating-current (AC) electroluminescent formats. Our discussion encompasses the materials, working principles, device architectures, failure mechanisms, optimization strategies, and practical applications. Through this review, we aim to deepen our understanding of the current challenges and future directions of perovskite-based flexible light-emitting technologies, hoping to facilitate their potential commercial applications.

Application of Metal Halide Perovskite in Internet of Things.

The Internet of Things (IoT) technology connects the real and network worlds by integrating sensors and internet technology, which has greatly changed people's lifestyles, showing its broad application prospects. However, traditional materials for the sensors and power components used in the IoT limit its development for high-precision detection, long-term endurance, and multi-scenario applications. Metal halide perovskite, with unique advantages such as excellent photoelectric properties, an adjustable bandgap, flexibility, and a mild process, exhibits enormous potential to meet the requirements for IoT development. This paper provides a comprehensive review of metal halide perovskite's application in sensors and energy supply modules within IoT systems. Advances in perovskite-based sensors, such as for gas, humidity, photoelectric, and optical sensors, are discussed. The application of indoor photovoltaics based on perovskite in IoT systems is also discussed. Lastly, the application prospects and challenges of perovskite-based devices in the IoT are summarized.

Bipolar-resistive switching characteristics in lead-free inorganic double-halide perovskite-based memory devices

Bipolar-resistive switching characteristics in lead-free inorganic double-halide perovskite-based memory devices

Numerical analysis of hybrid perovskite solar cells with NiOx and TiO2 as the charge transport layer

ABSTRACT This work exposits a hybrid perovskite-based solar cell consisting of NiOx as an electron-blocking material and TiO2 as a hole-blocking material to enhance its performance. Because the EBL material is critical to increasing efficiency and stability in a perovskite-based photovoltaic device, NiOx is being taken as a blocking material for improved reliability. It is also cost-effective and shows less hysteresis in contrast with alternative EBL materials. In addition, a wide band gap material like TiO2 as HBL is considered for enhancing carrier transportation phenomena that improve device performance. The efficiency of the suggested photovoltaic device is assessed in terms of solar parameters using the TCAD numerical simulation tool, accounting for the impacts of the thickness of the perovskite material, the density of defects, and the blocking material doping concentration. Also, the temperature reliability study is thoroughly investigated, considering all the optimised thicknesses of different layers and their optimised doping level.

Orthogonal Electrochemical Stability of Bulk and Surface in Lead Halide Perovskite Thin Films and Nanocrystals.

Lead halide perovskites have attracted significant attention for their wide-ranging applications in optoelectronic devices. A ubiquitous element in these applications is that charging of the perovskite is involved, which can trigger electrochemical degradation reactions. Understanding the underlying factors governing these degradation processes is crucial for improving the stability of perovskite-based devices. For bulk semiconductors, the electrochemical decomposition potentials depend on the stabilization of atoms in the lattice-a parameter linked to the material's solubility. For perovskite nanocrystals (NCs), electrochemical surface reactions are strongly influenced by the binding equilibrium of passivating ligands. Here, we report a spectro-electrochemical study on CsPbBr3 NCs and bulk thin films in contact with various electrolytes, aimed at understanding the factors that control cathodic degradation. These measurements reveal that the cathodic decomposition of NCs is primarily determined by the solubility of surface ligands, with diminished cathodic degradation for NCs in high-polarity electrolyte solvents where ligand solubilities are lower. However, the solubility of the surface ligands and bulk lattice of NCs are orthogonal, such that no electrolyte could be identified where both the surface and bulk are stabilized against cathodic decomposition. This poses inherent challenges for electrochemical applications: (i) The electrochemical stability window of CsPbBr3 NCs is constrained by the reduction potential of dissolved Pb2+ complexes, and (ii) cathodic decomposition occurs well before the conduction band can be populated with electrons. Our findings provide insights to enhance the electrochemical stability of perovskite thin films and NCs, emphasizing the importance of a combined selection of surface passivation and electrolyte.

Synchrotron Radiation-Based In Situ GIWAXS for Metal Halide Perovskite Solution Spin-Coating Fabrication.

Solution-processable perovskite-based devices are potentially very interesting because of their relatively cheap fabrication cost but outstanding optoelectronic performance. However, the solution spin-coating process involves complicated processes, including perovskite solution droplets, nucleation of perovskite, and formation of intermediate perovskite films, resulting in complicated crystallization pathways for perovskite films under annealing. Understanding and therefore controlling the fabrication process of perovskites is difficult. Recently, synchrotron radiation-based in situ grazing-incidence wide-angle X-ray scattering (GIWAXS) techniques, which possess the advantages of high collimation, high resolution, and high brightness, have enabled to bridge complicated perovskite structure information with device performance by revealing the real-time crystallization pathways of perovskites during the spin-coating process. Herein, the developments of synchrotron radiation-based in situ GIWAXS are discussed in the study of the crystallization process of perovskites, especially revealing the important crystallization mechanisms of state-of-the-art perovskite optoelectronic devices with high performance. At the end, several potential applications and challenges associated with in situ GIWAXS techniques for perovskite-based devices are highlighted.

Energy-band gradient structure originated from longitudinal phase segregation of mixed halide perovskite single crystal

Energy-band gradient halide perovskites are highly desired candidates for fabricating high performance optoelectronic devices. Here, we demonstrate that a mixed halide perovskite single crystal undergoes phase segregation in the longitudinal direction under above-bandgap light illumination. As a result, a micron thick layer with vertically gradient halide composition and thus graded valence band edge is generated at the crystal surface. The resultant gradient structure can facilitate the hole extraction at its interface with a hole transport layer. The longitudinal phase segregation of mixed halide perovskite single crystal is likely driven by abundant defects at the surface. Moreover, the segregation rate is increased in air compared to nitrogen probably due to the combined effect of oxygen and moisture. These findings not only deepen the understanding of phase segregation mechanism in mixed halide perovskite, but also indicate a promising avenue of fabricating vertically energy-band gradient perovskite and enhancing the perovskite-based optoelectronic device performance.

Nitrogen-rich carbon dots as the antisolvent additive for perovskite-based photovoltaic devices

Solution-processed perovskite solar cells (PSCs) have demonstrated a tremendous growth in power conversion efficiency (PCE). A high-quality, defect-free perovskite-based active layer is a key point to enhance PSC performance. Introduction of additives and interlayers have proved to be an effective tool to passivate surface defects, control crystal growth, and improve PSC stability. Antisolvent engineering has emerged recently as a new approach, which aims to adjust perovskite layer properties and enhance the PCE and stability of PSC devices. Here, we demonstrate that carbon dots (CDs) may serve as a prospective additive for antisolvent engineering. Nitrogen-rich amphiphilic CDs were synthesized from amines by a solvothermal method and used as an additive to chlorobenzene for a perovskite layer fabrication. The interaction between perovskite and functional groups in CDs promotes improved crystallization of an active perovskite layer and defects passivation, bringing higher PSCs efficiency, stability, and suppressed hysteresis. Under optimized CD concentration, the maximum PCE increased by 34% due to the improved short-circuit current and fill factor, and the device maintains 87% of its initial efficiency after 6 d of storage under ambient conditions.

Temperature-Dependent Structural and Optoelectronic Properties of the Layered Perovskite 2-Thiophenemethylammonium Lead Iodide.

Improved knowledge of the influence of temperature upon layered perovskites is essential to enable perovskite-based devices to operate over a broad temperature range and to elucidate the impact of structural changes upon the optoelectronic properties. We examined the Ruddlesden-Popper layered perovskite 2-thiophenemethylammonium lead iodide (ThMA2PbI4) and observed a structural phase transition between a high- and a low-temperature phase at 220 K using temperature-dependent X-ray diffraction, UV-visible absorption, and photoluminescence (PL) spectroscopy. The structural phase transition altered the tilt pattern of the inorganic octahedra layer, modifying the absorption and PL spectra. Further, we found a narrow and intense additional PL peak in the low-temperature phase, which we assigned to radiative emission from a defect-bound exciton state. In both phases we determined the thermal expansion coefficient and found values similar to those of cubic 3D perovskites, i.e., larger than those of typical substrates such as glass. These results demonstrate that the organic spacer plays a critical role in controlling the temperature-dependent structural and optoelectronic properties of layered perovskites and suggests more widely that strain management strategies may be needed to fully utilize layered perovskites in device applications.

Light-induced multilevel resistive switching in cesium-doped lead-free halide double perovskite memory device

A series of (CH3NH3)2-xCsxAgBiBr6 films (x=0, 0.1, 0.2, 0.3, 0.4) were fabricated on ITO/glass substrates through the sol-gel method. 15 % Cs doping (x=0.3) was the optimal condition for enhancing the film quality and achieving nonvolatile bipolar resistive switching (BRS) performance in the devices. The on/off ratio in the (CH3NH3)1.7Cs0.3AgBiBr6 (Cs-MAABB-3)-based RS device reached 7.7×104, high and low resistance states were maintained for over 104 s. Under different light intensities with a wavelength of 430 nm, six distinct resistance states were recorded at −0.3 V in the Au/Cs-MAABB-3/ITO/glass device. These multilevel states remained after 5000 s and 650 cycles, indicating the excellent retention and endurance of multilevel RS memory in the Au/Cs-MAABB-3/ITO/glass device. The RS behavior in this device followed the trap-controlled space charge-limited current and conductive filament models. Cs-doping increased the concentration of intrinsic vacancies appropriately, leading to a more prominent RS effect. With varying intensities of illumination, the change of Schottky-like barrier at the Au/Cs-MAABB-3 interface, modulated by the photo-induced carriers, affected the multilevel resistance states in the device. The excellent multilevel RS performance was observed for the first time in the Cs-MAABB-3-based device. It presents broad possibilities for improving high-density memory in lead-free halide double perovskite-based devices.

Real-time detection of aging status of methylammonium lead iodide perovskite thin films by using terahertz time-domain spectroscopy

The inadequate stability of organic–inorganic hybrid perovskites remains a significant barrier to their widespread commercial application in optoelectronic devices. Aging phenomena profoundly affect the optoelectronic performance of perovskite-based devices. In addition to enhancing perovskite stability, the real-time detection of aging status, aimed at monitoring the aging progression, holds paramount importance for both fundamental research and the commercialization of organic–inorganic hybrid perovskites. In this study, the aging status of perovskite was real-time investigated by using terahertz time-domain spectroscopy. Our analysis consistently revealed a gradual decline in the intensity of the absorption peak at 0.968 THz with increasing perovskite aging. Furthermore, a systematic discussion was conducted on the variations in intensity and position of the terahertz absorption peaks as the perovskite aged. These findings facilitate the real-time assessment of perovskite aging, providing a promising method to expedite the commercialization of perovskite-based optoelectronic devices.Graphical