High-Quality Ruddlesden-Popper Perovskite Film Formation for High-Performance Perovskite Solar Cells

High-Entropy Perovskite Oxides as a Family of Electrocatalysts for Efficient and Selective Nitrogen Oxidation

Electrocatalytic nitrogen oxidation reaction (NOR) can convert nitrogen (N2) into nitrate (NO3-) under ambient conditions, providing an attractive approach for synthesis of NO3-, alternative to the current approach involving the harsh Haber-Bosch and Ostwald oxidation processes that necessitate high temperature, high pressure, and substantial carbon emission. Developing efficient NOR catalysts is a prerequisite, which remains a formidable challenge, owing to the weak activation/dissociation of N2. A variety of NOR electrocatalysts have been developed, but their NOR kinetics are still extremely sluggish, resulting in inferior Faradaic Efficiencies. Here, we report a high-entropy Ru-based perovskite oxide (denoted as Ru-HEP) that can function as a high-performance NOR catalyst and exhibit a high NO3- yield rate of 39.0 μmol mg-1 h-1 with a Faradaic Efficiency of 32.8%. Both our experimental results and theoretical calculations suggest that the high-entropy configuration of Ru-HEP perovskite oxide can markedly enhance the oxygen-vacancy concentration, where the Ru sites and their neighboring oxygen vacancies can serve as unsaturated centers and decrease the overall energy barrier for N2 electrooxidation, thereby leading to promoted NOR kinetics. This work presents an alternative avenue for promoting NOR catalysis on perovskite oxides through the high-entropy engineering strategy.

Complex Metal Oxides as Emerging Inorganic Hole-Transporting Materials for Perovskite Solar Cells

Perovskite solar cells (PSCs) have achieved revolutionary progress during the past decades with a rapidly boosting rate in power conversion efficiencies from 3.8% to 26.1%. However, high-efficiency PSCs with organic hole-transporting materials (HTMs) suffer from inferior long-term stability and high costs. The replacement of organic HTMs with inorganic counterparts such as metal oxides can solve the above-mentioned problems to realize highly robust and cost-effective PSCs. Nevertheless, the widely used simple metal oxide-based HTMs are limited by the low conductivity and poor light transmittance due to the fixed atomic environment. As an emerging family of inorganic HTMs, complex metal oxides with superior structural/compositional flexibility have attracted rapidly increasing interest recently, showing superior carrier conductivity/mobility and superb light transmittance. Herein, the recent advancements in the design and development of complex metal oxide-based HTMs for high-performance PSCs are summarized by emphasizing the superiority of complex metal oxides as HTMs over simple metal oxide-based counterparts. Consequently, several distinct strategies for the design of complex metal oxide-based HTMs are proposed. Last, the future directions and remaining challenges of inorganic complex metal oxide-based HTMs for PSCs are also presented. This review aims to provide valuable guidelines for the further advancements of robust, high-efficiency, and low-cost PSCs.

Hot-Injection Synthesis of Cesium Lead Halide Perovskite Nanowires with Tunable Optical Properties

Metal halide perovskite semiconductors have emerged as promising materials for various optoelectronic applications due to their unique crystal structure and outstanding properties. Among different forms, perovskite nanowires (NWs) offer distinct advantages, including a high aspect ratio, superior crystallinity, excellent light absorption, and carrier transport properties, as well as unique anisotropic luminescence properties. Understanding the formation mechanism and structure-property relationship of perovskite NWs is crucial for exploring their potential in optoelectronic devices. In this study, we successfully synthesized all-inorganic halide perovskite NWs with high aspect ratios and an orthorhombic crystal phase using the hot-injection method with controlled reaction conditions and surface ligands. These NWs exhibit excellent optical and electrical properties. Moreover, precise control over the halogen composition through a simple anion exchange process enables the tuning of the bandgap, leading to fluorescence emission, covering a wide range of colors across the visible spectrum. Consequently, these perovskite NWs hold great potential for efficient energy conversion and catalytic applications in photoelectrocatalysis.

Microencapsulated Perovskite Crystals via In Situ Permeation Growth from Polymer Microencapsulation-Expansion-Contraction Strategy: Advancing a Record Long-Term Stability beyond 10 000 h for Perovskite Solar Cells

Organic metal halide perovskite solar cells (PSCs) bearing both high efficiency and durability are predominantly challenged by inadequate crystallinity of perovskite. Herein, a polymer microencapsulation-expansion-contraction strategy is proposed for the first time to optimize the crystallization behavior of perovskite, typically by adeptly harnessing the swelling and deswelling characteristics of poly(4-acryloylmorpholine) (poly(4-AcM)) network on PbI2 surface. It can effectively retard the crystallization rate of perovskite, permitting meliorative crystallinity featured by increased grain size from 0.74 to 1.32 µm and reduced trap density from 1.12 × 1016 to 2.56 × 1015 cm-3. Moreover, profiting from the protection of poly(4-AcM) microencapsulation layer, the degradation of the perovskite is markedly suppressed. Resultant PSCs gain a robust power conversion efficiency (PCE) of 24.04%. Typically, they maintain 91% of their initial PCE for 13 008 h in a desiccated ambient environment and retain 92% PCE after storage for 4000 h with a relative humidity of 50 ± 10%, which is the state-of-the-art long-term stability among the reported contributions.

Interfacial Rivet to Fill Structural Defects: A Spacer Engineering Gift for 3D Solar Cells

The combination of 2D and 3D perovskites to passivate surfaces or interfaces with a high concentration of defects shows great promise for improving the efficiency of perovskite solar cells (PSCs). Constructing high-quality perovskite film systems by precisely modulating 2D perovskites with good morphologies and growth sites on 3D perovskite films remains a formidable challenge due to the complexity of spacer-engineered surface reactions. In this study, phase-pure 2D (HA)2(MA)n-1PbnI3n+1 perovskites with a controlled number of layers (n) are separated on a large scale and exploited as interface rivets to optimize 3D perovskite films, resulting in tunable film structural defects and grain boundaries. The optimized PSCs system benefits from a reduction in non-radiative recombination, resulting in improved optical performance, higher mobility, and lower trap density. The corresponding device achieves a champion power conversion efficiency (PCE) of more than 25%, especially for voltage (VOC) and fill factor (FF). The quality and uniformity of the perovskite films are further confirmed using large-area devices with an active area of 14 cm2, which exhibits a PCE of more than 21.24%. The high-quality thin-film system based on the 2D perovskites presented herein provides a new perspective for improving the efficiency and stability of PSCs.

Unveiling the Intrinsic Photophysics in Quasi-Two-Dimensional Perovskites

The two-dimensional (2D) perovskites have drawn intensive attention due to their unique stability and outstanding optoelectronic properties. However, the debate surrounding the spatial phase distribution and band alignment among different 2D phases in the quasi-2D perovskite has created complexities in understanding the carrier dynamics, hindering material and device development. In this study, we employed highly sensitive transient absorption spectroscopy to investigate the carrier dynamics of (BA)2(MA)n-1PbnI3n+1 quasi-2D Ruddlesden-Popper perovskite thin films, nominally prepared as n = 4. We observed the carrier-density-dependent electron and hole transfer dynamics between the 2D and three-dimensional (3D) phases. Under a low carrier density within the linear response range, we successfully resolved three ultrafast processes of both electron and hole transfers, spanning from hundreds of femtoseconds to several picoseconds, tens to hundreds of picoseconds, and hundreds of picoseconds to several nanoseconds, which can be attributed to lateral-epitaxial, partial-epitaxial, and disordered-interface heterostructures between 2D and 3D phases. By considering the interplay among the phase structure, band alignment, and carrier dynamics, we have proposed material synthesis strategies aimed at enhancing the carrier transport. Our results not only provide deep insights into an accurate intrinsic photophysics of quasi-2D perovskites but also inspire advancements in the practical application of these materials.

Advancements and Prospects in Perovskite Solar Cells: From Hybrid to All-Inorganic Materials

Hybrid perovskites, materials composed of metals and organic substances in their structure, have emerged as potential materials for the new generation of photovoltaic cells due to a unique combination of optical, excitonic and electrical properties. Inspired by sensitization techniques on TiO2 substrates (DSSC), CH3NH3PbBr3 and CH3NH3PbI3 perovskites were studied as a light-absorbing layer as well as an electron-hole pair generator. Photovoltaic cells based on per-ovskites have electron and hole transport layers (ETL and HTL, respectively), separated by an ac-tive layer composed of perovskite itself. Major advances subsequently came in the preparation methods of these devices and the development of different architectures, which resulted in an efficiency exceeding 23% in less than 10 years. Problems with stability are the main barrier to the large-scale production of hybrid perovskites. Partially or fully inorganic perovskites appear promising to circumvent the instability problem, among which the black perovskite phase CsPbI3 (α-CsPbI3) can be highlighted. In more advanced studies, a partial or total substitution of Pb by Ge, Sn, Sb, Bi, Cu or Ti is proposed to mitigate potential toxicity problems and maintain device efficiency.

Synergistic Passivation With Phenylpropylammonium Bromide for Efficient Inverted Perovskite Solar Cells

Inverted perovskite solar cells (PSCs) are a promising technology for commercialization due to their reliable operation and scalable fabrication. However, in inverted PSCs, depositing a high-quality perovskite layer comparable to those realized in normal structures still presents some challenges. Defects at grain boundaries and interfaces between the active layer and carrier extraction layer seriously hinder the power conversion efficiency (PCE) and stability of these cells. In this work, it is shown that synergistic bulk doping and surface treatment of triple-cation mixed-halide perovskites with phenylpropylammonium bromine (PPABr) can improve the efficiency and stability of inverted PSCs. The PPABr ligand is effective in eliminating halide vacancy defects and uncoordinated Pb2+ ions at both grain boundaries and interfaces. In addition, a 2D Ruddlesden-Popper (2D-RP) perovskite capping layer is formed on the surface of 3D perovskite by using PPABr post-treatment. This 2D-RP perovskite capping layer possesses a concentrated phase distribution ≈n = 2. This capping layer not only reduces interfacial non-radiative recombination loss and improves carrier extraction ability but also promotes stability and efficiency. As a result, the inverted PSCs achieve a champion PCE of over 23%, with an open-circuit voltage as high as 1.15 V and a fill factor of over 83%.

Super-tetragonal Sr4Al2O7 as a sacrificial layer for high-integrity freestanding oxide membranes

Identifying a suitable water-soluble sacrificial layer is crucial to fabricating large-scale freestanding oxide membranes, which offer attractive functionalities and integrations with advanced semiconductor technologies. Here, we introduce a water-soluble sacrificial layer, "super-tetragonal" Sr4Al2O7 (SAOT). The low-symmetric crystal structure enables a superior capability to sustain epitaxial strain, allowing for broad tunability in lattice constants. The resultant structural coherency and defect-free interface in perovskite ABO3/SAOT heterostructures effectively restrain crack formation during the water release of freestanding oxide membranes. For a variety of nonferroelectric oxide membranes, the crack-free areas can span up to a millimeter in scale. This compelling feature, combined with the inherent high water solubility, makes SAOT a versatile and feasible sacrificial layer for producing high-quality freestanding oxide membranes, thereby boosting their potential for innovative device applications.

Promoting Ruddlesden-Popper Perovskite Formation by Tailoring Spacer Intramolecular Interaction for Efficient and Stable Solar Cells

Low-dimensional Ruddlesden-Popper phase (LDRP) perovskites are widely studied in the field of photovoltaics due to their tunable energy-band properties, enhanced photostability, and improved environmental stability compared to the 3D perovskites. However, the insulating spacers with weak intramolecular interaction used in LDRP materials limit the out-of-plane charge transport, leading to poor device performance of LDRP perovskite solar cells (PSCs). Here, a functional ligand, 3-guanidinopropanoic acid (GPA), which is capable of forming strong intramolecular hydrogen bonds through the carboxylic acid group, is employed as an organic spacer for LDRP PSCs. Owing to the strong interaction between GPA molecules, high-quality LDRP (GPA)2 (MA)n-1 Pbn I3n+1 film with promoted formation of n = 5 phase, improved crystallinity, preferential vertical growth orientations, reduced trap-state density, and prolonged carrier lifetime is achieved using GPAI as the dimensionality regulator compared to butylamine hydroiodide (BAI). As a result, GPA-based LDRP PSC exhibits a champion power conversion efficiency of 18.16% that is much superior to the BA-based LDRP PSC (15.43%). Importantly, the optimized GPA-based LDRP PSCs without encapsulation show enhanced illumination, thermal, storage, and humidity stability compared to BA-based ones. This work provides new insights into producing high n value LDRP films and their efficient and stable PSCs.

Characterizing Spatial and Energetic Distributions of Trap States Toward Highly Efficient Perovskite Photovoltaics

Due to their greater opt electric performance, perovskite photovoltaics (PVs) present huge potential to be commercialized. Perovskite PV's high theoretical efficiency expands the available development area. The passivation of defects in perovskite films is crucial for approaching the theoretical limit. In addition to creating efficient passivation techniques, it is essential to direct the passivation approach by getting precise and real-time information on the trap states through measurements. Therefore, it is necessary to establish quantitative characterization methods for the trap states in energy and 3D spaces. The authors cover the characterization of the spatial and energy distributions of trap states in this article with an eye toward high-efficiency perovskite photovoltaics. After going over the strategies that have been created for characterizing and evaluating trap states, the authors will concentrate on how to direct the creative development of characterization techniques for trap states assessment and highlight the opportunities and challenges of future development. The 3D space and energy distribution mappings of trap states are anticipated to be realized. The review will give key guiding importance for further approaching the theoretical efficiency of perovskite photovoltaics, offering some future research direction and technological assistance for the development of appropriate targeted passivation technologies.

Oriented Perovskite Film from Laser Recrystallization in Magnetic Field

The orientation of crystals on the substrate and the presence of defects are critical factors in electro-optic performance. However, technical approaches to guide the orientational crystallization of electro-optical thin films remain challenging. Here, a novel physical method called magnetic-field-assisted pulse laser annealing (MAPLA) for controlling the orientation of perovskite crystals on substrates is reported. By inducing laser recrystallization of perovskite crystals under a magnetic field and with magnetic nanoparticles, the optical and magnetic fields are found to guide the orientational gathering of perovskite units into nanoclusters, resulting in perovskite crystals with preferred lattice orientation in (110) and (220) perpendicular to the substrate. The perovskite crystals obtained by MAPLA exhibit significantly larger grain size and fewer defects compared to those from pulsed laser annealing (PLA) and traditional thermal annealing, resulting in improved carrier lifetime and mobility. Furthermore, MAPLA demonstrates enhanced device performance, increasing responsivity and detectivity by two times, and photocurrent by nearly three orders compared with PLA. The introduction of Fe2 O3 nanoparticles during MAPLA not only improves crystal size and orientation but also significantly enhances long-term stability by preventing Pb2+ reduction. The MAPLA method has great potential for fabricating many electro-optical thin films with desired device properties and stability.

Recent Advances and Opportunities of Eco-Friendly Ternary Copper Halides: A New Superstar in Optoelectronic Applications

Recently, the newly-emerging lead-free metal-halide materials with less toxicity and superior optoelectronic properties have received wide attention as the safer and potentially more robust alternatives to lead-based perovskite counterparts. Among them, ternary copper halides (TCHs) have become a vital group due to their unique features, including abundant structural diversity, ease of synthesis, unprecedented optoelectronic properties, high abundance, and low cost. Although the recent efforts in this field have made certain progresses, some scientific and technological issues still remain unresolved. Herein, a comprehensive and up-to-date overview of recent progress on the fundamental characteristics of TCH materials and their versatile applications is presented, which contains topics such as: i) crystal and electronic structure features and synthesis strategies; ii) mechanisms of self-trapped excitons, luminescence regulation, and environmental stability; and iii) their burgeoning optoelectronic devices of phosphor-converted white light-emitting diodes (WLEDs), electroluminescent LEDs, anti-counterfeiting, X-ray scintillators, photodetectors, sensors, and memristors. Finally, the current challenges together with future perspectives on the development of TCH materials and applications are also critically described, which is considered to be critical for accelerating the commercialization of these rapidly evolving technologies.

Layered Low-Dimensional Ruddlesden-Popper and Dion-Jacobson Perovskites: From Material Properties to Photovoltaic Device Performance

Layered low-dimensional halide perovskites (LDPs) with multiple quantum well structure have shown increasing research interest in photovoltaic solar cell applications owing to their intrinsic moisture stability and favorable photophysical properties in comparison with their three-dimensional (3D) counterparts. The most common LDPs are Ruddlesden-Popper (RP) phases and Dion-Jacobson (DJ) phases, both of which have made significant research advances in efficiency and stability. However, distinct interlayer cations between RP and DJ phase lead to disparate chemical bonds and different perovskite structures, which endow RP and DJ perovskite with distinctive chemical and physical properties. Plenty of reviews have reported the research progress of LDPs but no summary has elaborated from the perspective of the merits and drawbacks of the RP and DJ phases. Herein, in this review, we offer a comprehensive expound on the merits and promises of RP and DJ LDPs from their chemical structure, physicochemical properties, and photovoltaic performance research progress aiming to provide a new insight into the dominance of RP and DJ phases. Then, we reviewed the recent progress on the synthesis and implementation of RP and DJ LDPs thin films and devices, as well as their optoelectronic properties. Finally, we discussed the possible strategies to resolve existing toughs to realize the desired high-performance LDPs solar cells.

Low-Dimensional and High-Crystallinity Carbonyl Cathodes Prepared by Physical Vapor Deposition for Green Aluminum Organic Batteries

We report a low-cost, high theoretical specific capacity π-conjugated organic compound (PTCDA) with C═O active centers as the cathode material in aluminum organic batteries. In addition, in order to improve the electron transport rate of PTCDA, a new method is proposed in this paper, which uses physical vapor deposition (PVD) method to make PTCDA recrystallize and grow on stainless steel and quartz glass substrates to improve its crystallinity. The increase of crystallinity expands the PTCDA π-π-conjugated system, making electrons more delocalized, which is beneficial to the transmission rate of electrons and ions, thereby enhancing the conductivity of the material. The experimental results show that compared with pristine PTCDA, PTCDA(Ss) and PTCDA(G) with higher crystallinity have better cycling stability and rate capability. The DFT (density functional theory) results indicated that the electron-deficient carbonyl group in the PTCDA molecule could reversibly coordinate/dissociate with the positively charged Al complex ions (AlCl2+). This research work provides insights into the rational design of low-dimensional, high-crystallinity, high-performance cathode materials for green aluminum organic batteries.

Synthesis of Layered Lead-Free Perovskite Nanocrystals with Precise Size and Shape Control and Their Photocatalytic Activity

Halide perovskites have attracted enormous attention due to their potential applications in optoelectronics and photocatalysis. However, concerns over their instability, toxicity, and unsatisfactory efficiency have necessitated the development of lead-free all-inorganic halide perovskites. A major challenge in designing efficient halide perovskites for practical applications is the lack of effective methods for producing nanocrystals with precise size and shape control. In this work, a layered perovskite, Cs4ZnSb2Cl12 (CZS), is found from calculations to exhibit size- and facet-dependent optoelectronic properties in the nanoscale, and thus, a colloidal method is used to synthesize the CZS nanoparticles with size-tunable morphologies: zero- (nanodots), one- (nanowires and nanorods), two- (nanoplates), and three-dimensional (nanopolyhedra). The growth kinetics of the CZS nanostructures, along with the effects of surface ligands, reaction temperature, and time were investigated. The optoelectronic properties of the nanocrystals varied with size due to quantum confinement effects and with shape due to anisotropy within the crystals and the exposure of specific facets. These properties could be modulated to enhance the visible-light photocatalytic performance for toluene oxidation. In particular, the 9.7 nm CZS nanoplates displayed a toluene to benzaldehyde conversion rate of 1893 μmol g-1 h-1 (95% selectivity), 500 times higher than the bulk synthesized CZS, and comparable with the reported photocatalysts. This study demonstrates the integration of theoretical calculations and synthesis, revealing an approach to the design and fabrication of novel, high-performance colloidal perovskite nanocrystals for optoelectronic and photocatalytic applications.

2D/3D Perovskite Photodetectors with High Response Frequency and Improved Stability Based on Thiophene-2-ethylamine and Dual Additives

Organic-inorganic lead halide perovskite materials have received great attention in recent years. However, the poor stability of these materials severely limits the commercial application of perovskite devices. Here, we used thiophene-2-ethylammonium iodide (TEAI) material as the organic spacer NH₄SCN and NH₄Cl as the dual additives to realize high-stability two-dimensional (2D)/three-dimensional (3D) perovskite thin films for perovskite photodetectors. Then, we investigated different effects of the dual additives on the orientation and crystallinity of the perovskite films. At room temperature, the optimized 2D/3D perovskite photodetectors exhibit good performance with high external quantum efficiency (EQE) (72%), large responsivity (0.36 A/W), high detectivity (2.46 × 10¹² Jones at the bias of 0 V), high response frequency (1.7 MHz), and improved stability (retains 90% photocurrent after 2000 h storage in RT and 10% RH conditions). Based on these devices, a dual-channel optical transport system and a light-intensity adder are achieved. The results of this study indicate that, with a simple process, the TEAI and dual-additives based 2D/3D perovskite photodetectors have promising applications in light-intensity adder and optical communication systems.

CH3NH3PbI3/Au/Mg0.2Zn0.8O Heterojunction Self-Powered Photodetectors with Suppressed Dark Current and Enhanced Detectivity

Interface engineering of the hole transport layer in CH₃NH₃PbI₃ photodetectors has resulted in significantly increased carrier accumulation and dark current as well as energy band mismatch, thus achieving the goal of high-power conversion efficiency. However, the reported heterojunction perovskite photodetectors exhibit high dark currents and low responsivities. Herein, heterojunction self-powered photodetectors, composed of p-type CH₃NH₃PbI₃ and n-type Mg_0.2Zn_0.8O, are prepared through the spin coating and magnetron sputtering. The obtained heterojunctions exhibit a high responsivity of 0.58 A/W, and the EQE of the CH₃NH₃PbI₃/Au/Mg_0.2Zn_0.8O heterojunction self-powered photodetectors is 10.23 times that of the CH₃NH₃PbI₃/Au photodetectors and 84.51 times that of the Mg_0.2ZnO_0.8/Au photodetectors. The built-in electric field of the p-n heterojunction significantly suppresses the dark current and improves the responsivity. Remarkably, in the self-supply voltage detection mode, the heterojunction achieves a high responsivity of up to 1.1 mA/W. The dark current of the CH₃NH₃PbI₃/Au/Mg_0.2Zn_0.8O heterojunction self-powered photodetectors is less than 1.4 × 10^-1 pA at 0 V, which is more than 10 times lower than that of the CH₃NH₃PbI₃ photodetectors. The best value of the detectivity is as high as 4.7 × 10¹² Jones. Furthermore, the heterojunction self-powered photodetectors exhibit a uniform photodetection response over a wide spectral range from 200 to 850 nm. This work provides guidance for achieving a low dark current and high detectivity for perovskite photodetectors.

Additive Engineering for Stable and Efficient Dion-Jacobson Phase Perovskite Solar Cells

Because of their better chemical stability and fascinating anisotropic characteristics, Dion-Jacobson (DJ)-layered halide perovskites, which owe crystallographic two-dimensional structures, have fascinated growing attention for solar devices. DJ-layered halide perovskites have special structural and photoelectronic features that allow the van der Waals gap to be eliminated or reduced. DJ-layered halide perovskites have improved photophysical characteristics, resulting in improved photovoltaic performance. Nevertheless, owing to the nature of the solution procedure and the fast crystal development of DJ perovskite thin layers, the precursor compositions and processing circumstances can cause a variety of defects to occur. The application of additives can impact DJ perovskite crystallization and film generation, trap passivation in the bulk and/or at the surface, interface structure, and energetic tuning. This study discusses recent developments in additive engineering for DJ multilayer halide perovskite film production. Several additive-assisted bulk and interface optimization methodologies are summarized. Lastly, an overview of research developments in additive engineering in the production of DJ-layered halide perovskite solar cells is offered.

Highly efficient and stable quasi two-dimensional perovskite solar cells via synergistic effect of dual additives

Recently, quasi two-dimensional (Q-2D) perovskites with alternating cations in the interlayer space (ACI) have attracted more attentions owing to their elevated stability compared with three-dimensional (3D) analogs. While the efficiency of the devices derived from Q-2D perovskites is much smaller than that based on 3D perovskites. Here, we utilized urea and methoxyamine hydrochloride (MOAH) dual additives to acquire high quality Q-2D ACI perovskite GA(MA)₅Pb₅I₁₆ (GA = guanidinium, MA = methylammonium) films. The efficiency of the perovskite solar cells (PSCs) derived from the Q-2D perovskite films induced by the synergistic effect of urea and MOAH dual additives increases to 20.32% from 17.21% for the devices without additive. This efficiency enhancement could be attributed to the enlarged grain size, improved crystallinity, optimized quantum well thickness distribution, and reduced trap states of the perovskite films. Moreover, the solar cells with dual additives present improved stability. The efficiency of devices with dual additives holds 95% of the original value after storage for 1600 h in ambient air. These results prove that the synergistic effect of urea and MOAH is an effective method to achieve highly efficient and stable Q-2D PSCs.

Doping Strategies for Promising Organic-Inorganic Halide Perovskites

Organic-inorganic halide perovskites (OIHPs) obtained tremendous attention due to their low cost and excellent properties. However, the stability and toxicity of Pb-based OIHPs (POIHPs), as well as the weakness of efficiency and stability in Sn-based OIHPs (SOIHPs), are still serious issues for commercial application. Notably, composition engineering is an effective and direct strategy for improving these issues along with the control and modification of properties. Recently, the doping strategies for POIHPs and SOIHPs are booming. Based on the relationship between properties and composition, the doping strategies for POIHPs and SOIHPs, aiming to provide a comprehensive review and guidance for the research are systematically summarized. Moreover, the doping strategies for Pb-Sn mixed OIHPs are also discussed. Finally, a brief perspective and conclusion toward future possible doping schemes and properties designment of POIHPs and SOIHPs are offered.

Highly Efficient and Stable 2D/3D Heterojunction Perovskite Solar Cells by In Situ Interface Modification with [(p-Fluorophenyl)ethyl]ammonium Acetate

2D/3D heterojunction perovskites, meaning a rationally prepared 2D capping layer on 3D perovskite films, have been demonstrated as an effective avenue for simultaneously enhancing the efficiency and stability in perovskite solar cells (PSCs). However, the mechanism of the 2D perovskite induced by organic agents is still not extensively studied. Here, we report 2D/3D heterojunction PSCs by in situ fabricating a 2D modified layer on 3D perovskite films with [(p-fluorophenyl)ethyl]ammonium acetate (FPEAAc). During the annealing process, FPEAAc melts and uniformly covers the 3D perovskite films. Then, the excess acetate salt is volatilized, eventually forming a compact 2D perovskite thin layer. On the one hand, the organic agents can effectively rivet onto the 3D perovskite surface, ensuring formation of the necessary 2D perovskites with hydrophobic FPEA⁺ ions. On the other hand, the reaction generates some PbI₂, which passivates the defects on 3D perovskite films and improves the interface contact, significantly enhancing the open-circuit voltage (V_OC) and fill factor (FF) in 2D/3D PSCs. The highest power conversion efficiency of 22.53% is achieved compared with 20.16% in 3D PSCs. The 2D/3D-heterojunction-structured PSCs modified by FPEAAc exhibit high stability, retaining about 90% of the initial device efficiency after 500 h at 85 °C and 40 ± 5% relative humidity. Our research provides a simple method to control the 2D perovskite layer formation and effectively enhance the performance and stability in 2D/3D heterojunction perovskite cells.

Rapid Interlayer Charge Separation and Extended Carrier Lifetimes due to Spontaneous Symmetry Breaking in Organic and Mixed Organic-Inorganic Dion-Jacobson Perovskites

Promising alternatives to three-dimensional perovskites, two-dimensional (2D) layered metal halide perovskites have proven their potential in optoelectronic applications due to improved photo- and chemical stability. Nevertheless, photovoltaic devices based on 2D perovskites suffer from poor efficiency owing to unfavorable charge carrier dynamics and energy losses. Focusing on the 2D Dion-Jacobson perovskite phase that is rapidly rising in popularity, we demonstrate that doping of complementary cations into the 3-(aminomethyl)piperidinium perovskite accelerates spontaneous charge separation and slows down charge recombination, both factors improving the photovoltaic performance. Employing ab initio nonadiabatic (NA) molecular dynamics combined with time-dependent density functional theory, we demonstrate that cesium doping broadens the bandgap by 0.4 eV and breaks structural symmetry. Assisted by thermal fluctuations, the symmetry breaking helps to localize electrons and holes in different layers and activates additional vibrational modes. As a result, the charge separation is accelerated. Simultaneously, the charge carrier lifetime grows due to shortened coherence time between the ground and excited states. The established relationships between perovskite composition and charge carrier dynamics provide guidelines toward future material discovery and design of perovskite solar cells.

Photoluminescence Modulation of Ruddlesden-Popper Perovskite via Phase Distribution Regulation

The intrinsic chaotic phase distribution in Ruddlesden-Popper Perovskite (RPP) hinders its further improvement of photoluminescence (PL) emission and limits its application in optical devices. In this work, we achieve the phase distribution regulation of RPP by varying the composition ratio of organic bulky spacer cations 1-naphthylmethylamine (NMA) and phenylethyl-ammonium (PEA), which is controllable and nondestructive for structures of RPP. By suppressing the small n-phase, the PL intensity emission of RPP is further improved. Through the time-resolved PL (TRPL) measurements, we find the PL lifetime of the sample with 66% PEA concentration increases with the temperature initially and possesses the highest values of τ1 and τ2 at ~255 K, indicating the immediate state assisting exciton radiative recombination, and it can be modulated by phase manipulation in RPP. The immediate state may outcompete other non-radiative decay channels for excited carriers, leading to the PL enhancement in RPP, and broadening its further application.

Metal Halide Perovskite Nanowires: Controllable Synthesis, Mechanism, and Application in Optoelectronic Devices

Metal halide perovskites are promising energy materials because of their high absorption coefficients, long carrier lifetimes, strong photoluminescence, and low cost. Low-dimensional halide perovskites, especially one-dimensional (1D) halide perovskite nanowires (NWs), have become a hot research topic in optoelectronics owing to their excellent optoelectronic properties. Herein, we review the synthetic strategies and mechanisms of halide perovskite NWs in recent years, such as hot injection, vapor phase growth, selfassembly, and solvothermal synthesis. Furthermore, we summarize their applications in optoelectronics, including lasers, photodetectors, and solar cells. Finally, we propose possible perspectives for the development of halide perovskite NWs.

Synthesis and Application of Catalytic Materials in Energy and Environment

Catalytic materials have become prominent in many high-tech fields in recent years [...]

Monovalent Copper Cation Doping Enables High-Performance CsPbIBr2-Based All-Inorganic Perovskite Solar Cells

Organic-inorganic perovskite solar cells (PSCs) have delivered the highest power conversion efficiency (PCE) of 25.7% currently, but they are unfortunately limited by several key issues, such as inferior humid and thermal stability, significantly retarding their widespread application. To tackle the instability issue, all-inorganic PSCs have attracted increasing interest due to superior structural, humid and high-temperature stability to their organic-inorganic counterparts. Nevertheless, all-inorganic PSCs with typical CsPbIBr₂ perovskite as light absorbers suffer from much inferior PCEs to those of organic-inorganic PSCs. Functional doping is regarded as a simple and useful strategy to improve the PCEs of CsPbIBr₂-based all-inorganic PSCs. Herein, we report a monovalent copper cation (Cu⁺)-doping strategy to boost the performance of CsPbIBr₂-based PSCs by increasing the grain sizes and improving the CsPbIBr₂ film quality, reducing the defect density, inhibiting the carrier recombination and constructing proper energy level alignment. Consequently, the device with optimized Cu⁺-doping concentration generates a much better PCE of 9.11% than the pristine cell (7.24%). Moreover, the Cu⁺ doping also remarkably enhances the humid and thermal durability of CsPbIBr₂-based PSCs with suppressed hysteresis. The current study provides a simple and useful strategy to enhance the PCE and the durability of CsPbIBr₂-based PSCs, which can promote the practical application of perovskite photovoltaics.

Halide Perovskite Crystallization Processes and Methods in Nanocrystals, Single Crystals, and Thin Films

Halide perovskite semiconductors with extraordinary optoelectronic properties have been fascinatedly studied. Halide perovskite nanocrystals, single crystals, and thin films have been prepared for various fields, such as light emission, light detection, and light harvesting. High-performance devices rely on high crystal quality determined by the nucleation and crystal growth process. Here, the fundamental understanding of the crystallization process driven by supersaturation of the solution is discussed and the methods for halide perovskite crystals are summarized. Supersaturation determines the proportion and the average Gibbs free energy changes for surface and volume molecular units involved in the spontaneous aggregation, which could be stable in the solution and induce homogeneous nucleation only when the solution exceeds a required minimum critical concentration (C_min ). Crystal growth and heterogeneous nucleation are thermodynamically easier than homogeneous nucleation due to the existent surfaces. Nanocrystals are mainly prepared via the nucleation-dominated process by rapidly increasing the concentration over C_min , single crystals are mainly prepared via the growth-dominated process by keeping the concentration between solubility and C_min , while thin films are mainly prepared by compromising the nucleation and growth processes to ensure compactness and grain sizes. Typical strategies for preparing these three forms of halide perovskites are also reviewed.

Stabilization of Perovskite Solar Cells: Recent Developments and Future Perspectives

Exceptional power conversion efficiency (PCE) of 25.7% in perovskite solar cells (PSCs) has been achieved, which is comparable with their traditional rivals (Si-based solar cells). However, commercialization-worthy efficiency and long-term stability remain a challenge. In this regard, there are increasing studies focusing on the interface engineering in PSC devices to overcome their poor technical readiness. Herein, the roles of electrode materials and interfaces in PSCs are discussed in terms of their PCEs and perovskite stability. All the current knowledge on the factors responsible for the rapid intrinsic and external degradation of PSCs is presented. Then, the roles of carbonaceous materials as substitutes for noble metals are focused on, along with the recent research progress in carbon-based PSCs. Furthermore, a sub-category of PSCs, that is, flexible PSCs, is considered as a type of exceptional power source due to their high power-to-weight ratios and figures of merit for next-generation wearable electronics. Last, the future perspectives and directions for research in PSCs are discussed, with an emphasis on their commercialization.

Copper-based metal halides for X-ray and photodetection

Copper-based metal halides have become important materials in the field of X-ray and photodetection due to their excellent optical properties, good environmental stability and low toxicity. This review presents the progress of research on crystal structure/morphology, photophysics/optical properties and applications of copper-based metal halides. We also discuss the challenges of copper-based metal halides with a perspective of their future research directions.

Precursor engineering for efficient and stable perovskite solar cells

The perovskite film prepared by the two-step spin coating method is widely used in photovoltaic devices due to its good film morphology and great reproducibility. However, there usually exists excessive lead iodide (PbI₂) in the perovskite film for this method, which is believed to passivate the grain boundaries (GBs) to increase the efficiency of the perovskite solar cells. Nevertheless, the excessive PbI₂at the GBs of perovskite is believed to induce the decomposition of the perovskite film and undermine the long-term stability of devices. In this study, we utilize precursor engineering to realize the preparation of perovskite solar cells with high efficiency and stability. The concentration of organic salts (AX: A = MA⁺, FA⁺; X = I^-, Cl^-) in the precursor solution for the second step of the two-step spin coating method is adjusted to optimize the perovskite light-absorbing layer so that the excessive PbI₂is converted into perovskite to obtain a smooth and pinhole-free perovskite film with high performance. Our results indicate that by adjusting the concentration of AX in the precursor solution, PbI₂in the film could be completely converted into perovskite without excessive AX residue. Both the efficiency and stability of the perovskite solar cells without excessive PbI₂have been significantly improved. A planar perovskite solar cell with the highest power conversion efficiency (PCE) of 21.26% was achieved, maintaining about 90% of the initial PCE after 300 h of storage in a dry air environment and in the dark, about 76% of the initial PCE after 300 h of continuous illumination of 1 Sun.

Near-room-temperature martensitic actuation profited from one-dimensional hybrid perovskite structure

Martensitic transformation, usually accompanied by ferroelastic and thermoelastic behaviors, is an interesting and useful mechanical-related property upon external stimuli. For molecular crystals, however, martensitic systems to show reversible stimuli-actuation behaviors are still limited because of a lack of designability and frequent crystal collapse due to large stress releases during the transformations. Here, a one-dimensional hybrid perovskite semiconductor (NMEA)PbI₃ (NMEA = N-methylethylammonium) was prepared by following a dimensionality reduction design principle. The crystal undergoes reversible ferroelastic and thermoelastic martensitic transformations, which are attributed to weak intermolecular interactions among the chains that easily trigger the interchain shearing movement. The actuation behavior occurring during the phase transition is very close to room temperature and demonstrated to behave as a mechanical actuator for switching. This work provides an effective approach to designing molecular actuators with promising applications in next-generation intelligence devices.

Strong two-photon absorption induced by energy funneling in chiral quasi-2D perovskites

Quasi-2D Ruddlesden-Popper-type perovskites (RPPs) exhibit excellent nonlinear optical properties due to their multiple quantum well structures with large exciton binding energy. Herein, we introduce chiral organic molecules into RPPs and investigate their optical properties. It is found that the chiral RPPs possess effective circular dichroism in the ultraviolet to visible wavelengths. Two-photon absorption (TPA)-induced efficient energy funneling from small- to large-n domains is observed in the chiral RPP films, which induces strong TPA with a coefficient up to 4.98 cm MW^-1. This work will broaden the application of quasi-2D RPPs in chirality-related nonlinear photonic devices.

Structural Dimensionality Dependence of the Band Gap in An+1BnX3n+1 Ruddlesden-Popper Perovskites: A Global Picture

Dimensionality engineering in A_n+1B_nX_3n+1 Ruddlesden-Popper (RP) perovskites has recently emerged as a promising tool for tuning the band gap to improve optoelectronic properties. However, the evolution of the band gap is dependent on the material; distinguishing the effects of different factors is urgently needed to guide the rational design of high-performance materials. Through first-principles calculations, we perform a systematic investigation of RP oxide, chalcogenide, and halide perovskites. The results reveal that in addition to the confinement effect and the change in octahedral rotation motions and/or amplitudes, interfacial rumpling and a change in the A-site cation coordination number also determine the evolution of the band gap. More importantly, we emphasize that the evolution of the band gap in RP perovskites is not dependent on the material family. Instead, the B-site frontier orbital type (s, p, and d) and bandwidth, A-site cation, interfacial rumpling, and structural distortions simultaneously determine the evolution of the band gap. These insights enable a complete and deeper understanding of various experimental observations.

Advances in Emerging Photonic Memristive and Memristive-Like Devices

Possessing the merits of high efficiency, low consumption, and versatility, emerging photonic memristive and memristive-like devices exhibit an attractive future in constructing novel neuromorphic computing and miniaturized bionic electronic system. Recently, the potential of various emerging materials and structures for photonic memristive and memristive-like devices has attracted tremendous research efforts, generating various novel theories, mechanisms, and applications. Limited by the ambiguity of the mechanism and the reliability of the material, the development and commercialization of such devices are still rare and in their infancy. Therefore, a detailed and systematic review of photonic memristive and memristive-like devices is needed to further promote its development. In this review, the resistive switching mechanisms of photonic memristive and memristive-like devices are first elaborated. Then, a systematic investigation of the active materials, which induce a pivotal influence in the overall performance of photonic memristive and memristive-like devices, is highlighted and evaluated in various indicators. Finally, the recent advanced applications are summarized and discussed. In a word, it is believed that this review provides an extensive impact on many fields of photonic memristive and memristive-like devices, and lay a foundation for academic research and commercial applications.

Aromatic Heterocyclic Organic Spacer Cation-Assisted Growth of Large-Grain-Size 2DRP Perovskite Film for Enhanced Solar Cell Performance

Organic spacer cations play an important role in the aggregation of two-dimensional Ruddlesden-Popper (2DRP) L'₂L_n-1B_nX_3n+1 perovskite precursors. Therefore, it is necessary to study how mixed A' spacer cations affect the aggregation behavior of precursors and the carrier transport properties of 2DRP films. Herein, a novel spacer cation 4-pyridinylmethylammonium (PyA) is introduced to prepare a new mixed spacer cation 2DRP (BA_1-xPyA_x)₂MA₃Pb₄I₁₃ perovskite. The incorporation of PyA suppresses the precursor aggregation and reduces the transformation energy of the sol-gel to the directional three-dimensional phase, leading to the formation of large-grain-size 2DRP perovskite films. The PyA-based 2DRP perovskite exhibits efficient carrier transport owing to fewer defects and suppressed nonradiative recombination. Thus, the champion efficiency of 13.01% is achieved for BA- and PyA-based devices. The unencapsulated PyA-based devices maintain 98% of their initial efficiency after storage under nitrogen atmosphere for 1200 h. This work paves the way for preparing a large-grain-size 2DRP perovskite by suppressing precursor aggregation.

Performance optimization strategies of halide perovskite-based mechanical energy harvesters

Halide perovskites, possessing unique electronic and photovoltaic properties, have been intensively investigated over the past decade. The excellent polarization, piezoelectricity, dielectricity and photoelectricity of halide perovskites provide new opportunities for the applications of mechanical energy harvesting. Although various studies have been conducted to develop halide perovskite-based triboelectric and piezoelectric nanogenerators, strategies for their electrical performance optimization are rarely mentioned. In this review, we systematically introduce the recent research progress of halide perovskite-based mechanical energy harvesters and summarize the different optimization strategies for improving both the piezoelectric and triboelectric output of the devices, bringing some inspiration to guide future material and structure design for halide perovskite-based energy devices. A summary of the current challenges and future perspectives is also presented, offering some possible directions for development in this emerging field.

Novel PHA Organic Spacer Increases Interlayer Interactions for High Efficiency in 2D Ruddlesden-Popper CsPbI3 Solar Cells

The two-dimensional (2D) Ruddlesden-Popper (RP) CsPbI₃ with hydrophobic organic spacers can significantly improve the environmental and phase stability of photovoltaic devices by suppressing ion migration and inducing steric hindrance. However, due to the multiple-quantum-well structure, these spacer cations lead to weak interactions in 2D RP CsPbI₃, which seriously affect the carrier transport. Here, a novel N-H-group-rich phenylhydrazine spacer, namely, PHA, was developed for 2D RP CsPbI₃ perovskite solar cells (PSCs). A series of characterizations confirm that the 2D perovskites using PHA spacers enhanced the N-H···I hydrogen-bonding interaction between the organic spacer cations and the [PbI₆]^4- inorganic layer and accelerated the crystallization rate of the perovskite film, which was beneficial to the preparation of high-quality films with preferred vertical orientation, large grain size, and dense morphology. Meanwhile, the trap state density of the as-prepared 2D RP perovskite films is significantly reduced to enable efficient charge carrier transport. As a result, the (PHA)₂Cs₄Pb₅I₁₆ PSCs achieved a performance of 16.23% with good environmental stability. This work provides a simple organic spacer selection scheme to realize interaction optimization in 2D RP CsPbI₃ to develop efficient and stable PSCs.

Ionic Liquid-Assisted Crystallization and Defect Passivation for Efficient Perovskite Solar Cells with Enhanced Open-Circuit Voltage

Perovskite materials have demonstrated many excellent properties in next-generation photovoltaic devices, but the intrinsic defects and the quality of perovskite film still limit the performance and stability of PSCs. Here, 1,3-dimethylimidazolium iodide (DMII) ionic liquid was employed as an additive to passivate the various defects and produce the high-quality perovskite film with enlarged grain sizes. DMII could act as an "ionic stabilizer" for passivating the point defects including the vacancies defects of organic cations and halogen anions of perovskite. At the same time, the extra problematic PbI₂ on surfaces and at grain boundaries of the perovskite film could also be reacted by DMII, leading to the reduction of recombination centers and trap states. On the other hand, the DMII ionic liquid with a "Ostwald ripening effect" could retard the crystallization process of perovskite crystals and yield better film quality with higher crystallinity, smoother morphology and larger grains. As a result, the optimal device achieved a champion power conversion efficiency (PCE) of 20.4 %. Particularly, the modified devices demonstrated a significant elevation in open-circuit voltage from 1.03 to 1.10 V. The hydrophobicity of perovskite films modified by DMII was enhanced and the un-encapsulated DMII devices retained 91 % of their initial PCE after aging 60 days under 15±5 % relative humidity.

Simultaneous Interfacial Modification and Defect Passivation for Wide-Bandgap Semitransparent Perovskite Solar Cells with 14.4% Power Conversion Efficiency and 38% Average Visible Transmittance

Perovskite materials offer a great potential in the application of semitransparent solar cells, owing to the tunable bandgap, ease of preparation and excellent photovoltaic property. A majority of works exhibit high average visible-light transmittance (AVT) for semitransparent perovskite solar cells (ST-PSCs) through decreasing perovskite thickness, leading to sacrificing the power conversion efficiency (PCE) of the device. Herein, a wide-bandgap (WBG) perovskite of Cs_0.2 FA_0.8 Pb(I_0.6 Br_0.4 )₃ is applied as absorber in ST-PSCs, which is a tremendous progress to balance both large PCE and high AVT. Moreover, a strategy of simultaneous interfacial modification and defect passivation is provided to enhance the performance of WBG ST-PSCs. Consequently, an inverted planar structure WBG perovskite solar cell (PSC) achieves 15.06% of PCE with excellent stability by restraining the interfacial energy loss and suppressing the nonradiative recombination. Furthermore, the ST-PSC obtains high PCE of 14.40% with an AVT of 38% by means of optimizing the transparent electrode. This work provides an efficient and simple method to improve the performance and AVT of ST-PSCs for the application in building-integrated photovoltaics.

Recent Advances in Nanostructured Inorganic Hole−Transporting Materials for Perovskite Solar Cells

Organic−inorganic halide perovskite solar cells (PSCs) have received particular attention in the last decade because of the high−power conversion efficiencies (PCEs), facile fabrication route and low cost. However, one of the most crucial obstacles to hindering the commercialization of PSCs is the instability issue, which is mainly caused by the inferior quality of the perovskite films and the poor tolerance of organic hole−transporting layer (HTL) against heat and moisture. Inorganic HTL materials are regarded as promising alternatives to replace organic counterparts for stable PSCs due to the high chemical stability, wide band gap, high light transmittance and low cost. In particular, nanostructure construction is reported to be an effective strategy to boost the hole transfer capability of inorganic HTLs and then enhance the PCEs of PSCs. Herein, the recent advances in the design and fabrication of nanostructured inorganic materials as HTLs for PSCs are reviewed by highlighting the superiority of nanostructured inorganic HTLs over organic counterparts in terms of moisture and heat tolerance, hole transfer capability and light transmittance. Furthermore, several strategies to boost the performance of inorganic HTLs are proposed, including fabrication route design, functional/selectively doping, morphology control, nanocomposite construction, etc. Finally, the challenges and future research directions about nanostructured inorganic HTL−based PSCs are provided and discussed. This review presents helpful guidelines for the design and fabrication of high−efficiency and durable inorganic HTL−based PSCs.

Polarized Molecule 4-(Aminomethyl) Benzonitrile Hydrochloride for Efficient and Stable Perovskite Solar Cells

The rapid development of perovskite solar cells (PSCs) makes it one of the most competitive photovoltaic devices in the field of new energy. However, the suboptimal performance and poor stability caused by numerous defects are still the main factors limiting the development of PSCs. Herein, a polarized molecule additive of 4-(aminomethyl) benzonitrile hydrochloride (AMBNCl) is introduced into perovskite. Owing to its special polar electron density distribution, -C≡N group, -NH3+ terminal, and Cl- ions, the modification of AMBNCl can improve the quality of perovskite crystal growth, passivate the defects of Pb2+, adjust the energy level array between the perovskite layer and hole-transport layer, and alleviate the carrier nonradiative recombination. As a result, the AMBNCl-modified device achieves a champion efficiency of 23.52%. The unpacked device still maintained 91.2% of its original efficiency after storing in an air environment (RH ∼40%, 25 °C) for 50 days.

PEDOT:PSS/CuCl Composite Hole Transporting Layer for Enhancing the Performance of 2D Ruddlesden-Popper Perovskite Solar Cells

Poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) is a popular hole transport layer (HTL) in 2D Ruddlesden-Popper (RP) perovskite solar cell (PSCs) due to its highly conductive, transparent, and solution-processable characteristics. However, fundamental questions such as its strong acidity or mismatched energy level with the 2D RP photoactive layer often restrict the performance and stability of devices. Herein, copper chloride (CuCl), a common direct band gap semiconductor, is doped into PEDOT:PSS, lowering the acidity and tuning the work function of PEDOT:PSS. Due to the improved wettability and the existing chloride in the PEDOT:PSS/CuCl composite substrate, the coated 2D perovskite films exhibit uniform morphology, vertically oriented crystal growth, and enhanced crystallinity. In comparison with controlled devices, the PEDOT:PSS/CuCl based inverted 2D RP PSCs show a maximum power conversion efficiency of 13.36% and long-term stability. The modified PEDOT:PSS overcomes intrinsic imperfections by doping CuCl, indicating that it has a lot of promise for mass production in electrical devices.

High-performance Ruddlesden-Popper two-dimensional perovskite solar cells via solution processed inorganic charge transport layers

Two-dimensional (2D) layered halide perovskites have been shown to enable improved long-term stability in comparison to the well-known three-dimensional hybrid organic-inorganic halide perovskites. The optoelectronic properties of the 2D perovskites are strongly influenced by the chemical nature of the charge transport layer. In this work, we fabricated Ruddlesden-Popper 2D perovskite solar cells (PSCs) using solution processed inorganic NiO_x and a C₆₀ : C₇₀ (1 : 1) mixture as the hole and electron transport layers, which significantly improved the performance of the 2D PSCs. Time resolved photoluminescence measurements indicate the shortened lifetime of excitons, which demonstrates the excellent charge extraction properties. The PSCs based on these inorganic charge transport materials (CTMs) exhibit an average power conversion efficiency (PCE) of 14.1%, which is higher than that (12.3%) of PSCs using organic CTMs of poly(3,4-ethylenedioxythiophene) : poly(styrenesulfonate) (PEDOT:PSS) and phenyl-C61-butyric acid methyl ester (PCBM). Compared with PEDOT:PSS and PCBM based cases, the PSCs using inorganic CTMs also show improved long-term stability, with the PCE degradation significantly suppressed from 20% to 12% after a measurement of 15 days. The best PSCs using NiO_x and C₆₀ : C₇₀ show a high PCE of 14.4%, with a stable power output and negligible hysteresis.

Recent Progress in Lanthanide-Doped Inorganic Perovskite Nanocrystals and Nanoheterostructures: A Future Vision of Bioimaging

All-inorganic lead halide perovskite nanocrystals have great potential in optoelectronics and photovoltaics. However, their biological applications have not been explored much owing to their poor stability and shallow penetration depth of ultraviolet (UV) excitation light into tissues. Interestingly, the combination of all-inorganic halide perovskite nanocrystals (IHP NCs) with nanoparticles consisting of lanthanide-doped matrix (Ln NPs, such as NaYF₄:Yb,Er NPs) is stable, near-infrared (NIR) excitable and emission tuneable (up-shifting emission), all of them desirable properties for biological applications. In addition, luminescence in inorganic perovskite nanomaterials has recently been sensitized via lanthanide doping. In this review, we discuss the progress of various Ln-doped all-inorganic halide perovskites (LnIHP). The unique properties of nanoheterostructures based on the interaction between IHP NCs and Ln NPs as well as those of LnIHP NCs are also detailed. Moreover, a systematic discussion of basic principles and mechanisms as well as of the recent advancements in bio-imaging based on these materials are presented. Finally, the challenges and future perspectives of bio-imaging based on NIR-triggered sensitized luminescence of IHP NCs are discussed.

2D Material and Perovskite Heterostructure for Optoelectronic Applications

Optoelectronic devices are key building blocks for sustainable energy, imaging applications, and optical communications in modern society. Two-dimensional materials and perovskites have been considered promising candidates in this research area due to their fascinating material properties. Despite the significant progress achieved in the past decades, challenges still remain to further improve the performance of devices based on 2D materials or perovskites and to solve stability issues for their reliability. Recently, a novel concept of 2D material/perovskite heterostructure has demonstrated remarkable achievements by taking advantage of both materials. The diverse fabrication techniques and large families of 2D materials and perovskites open up great opportunities for structure modification, interface engineering, and composition tuning in state-of-the-art optoelectronics. In this review, we present comprehensive information on the synthesis methods, material properties of 2D materials and perovskites, and the research progress of optoelectronic devices, particularly solar cells and photodetectors which are based on 2D materials, perovskites, and 2D material/perovskite heterostructures with future perspectives.