Atomic Model for Alkali Metal-Doped Tin-Lead Mixed Perovskites: Insight from Quantum Dynamics

Defects such as metal vacancies act as nonradiative recombination centers to deteriorate the photoelectric properties of metal halide perovskites. Nonadiabatic molecular dynamics has demonstrated that alkali metal dopants markedly improve the performance of mixed tin-lead perovskites. Alkali dopants increase the formation energy of tin vacancies to 1 eV, so that the defect concentration is decreased. When tin vacancies exist, alkali metals are easily doped into perovskites. Tin vacancies produce iodine trimers that create midgap states and cause rapid electron-hole recombination. Alkali metal additives eliminate the trap state, weaken nonadiabatic coupling, and decelerate charge recombination with a coefficient of ≤5.5 compared with the performance of the defective tin-lead mixed perovskite. Our research has constructed a theoretical model at the atomic level for alkali metal passivation that enhances defect tolerance of tin-lead mixed perovskites, generating valuable inspiration for optimizing high-performance perovskites.

Recent developments in lead-free bismuth-based halide perovskite nanomaterials for heterogeneous photocatalysis under visible light

Halide perovskite materials, especially lead-based perovskites, have been widely used for optoelectronic and catalytic applications. However, the high toxicity of the lead element is a major concern that directs the research work toward lead-free halide perovskites, which could utilize bismuth as a promising candidate. Until now, the replacement of lead by bismuth in perovskites has been well studied by designing bismuth-based halide perovskite (BHP) nanomaterials with versatile physical-chemical properties, which are emerging in various application fields, especially heterogeneous photocatalysis. In this mini-review, we present a brief overview of recent progress in BHP nanomaterials for photocatalysis under visible light. The synthesis and physical-chemical properties of BHP nanomaterials have been comprehensively summarized, including zero-dimensional, two-dimensional nanostructures and hetero-architectures. Later, we introduce the photocatalytic applications of these novel BHP nanomaterials with visible-light response, improved charge separation/transport and unique catalytic sites. Due to advanced nano-morphologies, a well-designed electronic structure and an engineered surface chemical micro-environment, BHP nanomaterials demonstrate enhanced photocatalytic performance for hydrogen generation, CO₂ reduction, organic synthesis and pollutant removal. Finally, the challenges and future research directions of BHP nanomaterials for photocatalysis are discussed.

Intricate Reaction Pathways on CH3NH3PbI3 Photocatalysts in Aqueous Solution Unraveled by Single-Particle Spectroscopy

Organic-inorganic hybrid perovskites such as MAPbI₃ (MA⁺ = CH₃NH₃⁺) have emerged as promising materials for solar cells and light-emitting devices. Despite their poor stability against moisture, perovskites work as hydrogen-producing photocatalysts or photosensitizers in perovskite-saturated aqueous solutions. However, the fundamental understanding of how chemical species or support materials in the solution affect the dynamics of the photogenerated charges in perovskites is still insufficient. In this study, we investigated the photoluminescence (PL) properties of MAPbI₃ nanoparticles in aqueous media at the single-particle level. A remarkable PL blinking phenomenon, along with significant decreases in the PL intensity and lifetime compared to those in ambient air, suggested temporal fluctuations in the trapping rates of photogenerated holes by chemical species (I^- and H₃PO₂) in the solution. Moreover, electron transfer from the excited MAPbI₃ to Pt-modified TiO₂ proceeds in a concerted fashion for photocatalytic hydrogen evolution under the dynamic solid-solution equilibrium condition.

Deciphering the Roles of MA-Based Volatile Additives for α-FAPbI3 to Enable Efficient Inverted Perovskite Solar Cells

Functional additives that can interact with the perovskite precursors to form the intermediate phase have been proven essential in obtaining uniform and stable α-FAPbI₃ films. Among them, Cl-based volatile additives are the most prevalent in the literature. However, their exact role is still unclear, especially in inverted perovskite solar cells (PSCs). In this work, we have systematically studied the functions of Cl-based volatile additives and MA-based additives in formamidinium lead iodide (FAPbI₃)-based inverted PSCs. Using in situ photoluminescence, we provide clear evidence to unravel the different roles of volatile additives (NH₄Cl, FACl, and MACl) and MA-based additives (MACl, MABr, and MAI) in the nucleation, crystallization, and phase transition of FAPbI₃. Three different kinds of crystallization routes are proposed based on the above additives. The non-MA volatile additives (NH₄Cl and FACl) were found to promote crystallization and lower the phase-transition temperatures. The MA-based additives could quickly induce MA-rich nuclei to form pure α-phase FAPbI₃ and dramatically reduce phase-transition temperatures. Furthermore, volatile MACl provides a unique effect on promoting the growth of secondary crystallization during annealing. The optimized solar cells with MACl can achieve an efficiency of 23.1%, which is the highest in inverted FAPbI₃-based PSCs.

Flexible Organic-Inorganic Halide Perovskite-Based Diffusive Memristor for Artificial Nociceptors

With the current evolution in the artificial intelligence technology, more biomimetic functions are essential to execute increasingly complicated tasks and respond to challenging work environments. Therefore, an artificial nociceptor plays a significant role in the advancement of humanoid robots. Organic-inorganic halide perovskites (OHPs) have the potential to mimic the biological neurons due to their inherent ion migration. Herein, a versatile and reliable diffusive memristor built on an OHP is reported as an artificial nociceptor. This OHP diffusive memristor showed threshold switching properties with excellent uniformity, forming-free behavior, a high I_ON/I_OFF ratio (10⁴), and bending endurance over >10² cycles. To emulate the biological nociceptor functionalities, four significant characteristics of the artificial nociceptor, such as threshold, no adaptation, relaxation, and sensitization, are demonstrated. Further, the feasibility of OHP nociceptors in artificial intelligence is being investigated by fabricating a thermoreceptor system. These findings suggest a prospective application of an OHP-based diffusive memristor in the future neuromorphic intelligence platform.

Spin-Electric Coupling in Lead Halide Perovskites

Lead halide perovskites enjoy a number of remarkable optoelectronic properties. To explain their origin, it is necessary to study how electromagnetic fields interact with these systems. We address this problem here by studying two classical quantities: Faraday rotation and the complex refractive index in a paradigmatic perovskite CH_{3}NH_{3}PbBr_{3} in a broad wavelength range. We find that the minimal coupling of electromagnetic fields to the k·p Hamiltonian is insufficient to describe the observed data even on the qualitative level. To amend this, we demonstrate that there exists a relevant atomic-level coupling between electromagnetic fields and the spin degree of freedom. This spin-electric coupling allows for quantitative description of a number of previous as well as present experimental data. In particular, we use it here to show that the Faraday effect in lead halide perovskites is dominated by the Zeeman splitting of the energy levels and has a substantial beyond-Becquerel contribution. Finally, we present general symmetry-based phenomenological arguments that in the low-energy limit our effective model includes all basis coupling terms to the electromagnetic field in the linear order.

Combining negative photoconductivity and resistive switching towards in-memory logic operations

A family of rudorffites based on silver-bismuth-iodide shows a transition from a conventional positive photoconductivity (PPC) to an unusual negative photoconductivity (NPC) upon variation in the precursor stoichiometry while forming the rudorffites. The NPC has arisen in silver-rich rudorffites due to the generation of illumination-induced trap-states which prompted the recombination of charge carriers and thereby a decrease in the conductivity of the compounds. In addition to photoconductivity, sandwiched devices based on all the rudorffites exhibited resistive switching between a pristine high resistive state (HRS) and a low resistive state (LRS) under a suitable voltage pulse; the switching process, which is reversible, is associated with a memory phenomenon. The devices based on NPC-exhibiting rudorffites switched to the HRS under illumination as well. That is, the resistive state of the devices could be controlled through both electrical and optical inputs. We employed such interesting optoelectronic properties of NPC-exhibiting rudorffites to exhibit OR logic gate operation. Because the devices could function as a logic gate and store the resistive state as well, we concluded that the materials could be an ideal candidate for in-memory logic operations.

Enhanced Circularly Polarized Photoluminescence of Chiral Perovskite Films by Surface Passivation with Chiral Amines

Hybrid organic-inorganic perovskites have shown promise in circularly polarized light source applications when chirality has been introduced. Circularly polarized photoluminescence (CPL) is a significant tool for investigating the chiroptical properties of perovskites. However, further research is still urgently needed, especially with regard to optimization. Here we demonstrate that chiral ligands can influence the electronic structure of perovskites, increasing the asymmetry and emitting circularly polarized photons in photoluminescence. After the modification of chiral amines, the defects of films are passivated, leading to enhanced radiation recombination for which more circularly polarized photons are emitted. Meanwhile, the modification increases the asymmetry in the electronic structure of perovskites, manifested by an increase in the magnetic dipole moment from 0.166 to 0.257 μ_B and an enhanced CPL signal. This approach offers the possibility of fabricating and refining circularly polarized light-emitting diodes.

Intrinsic Formamidinium Tin Iodide Nanocrystals by Suppressing the Sn(IV) Impurities

The long search for nontoxic alternatives to lead halide perovskites (LHPs) has shown that some compelling properties of LHPs, such as low effective masses of carriers, can only be attained in their closest Sn(II) and Ge(II) analogues, despite their tendency toward oxidation. Judicious choice of chemistry allowed formamidinium tin iodide (FASnI₃) to reach a power conversion efficiency of 14.81% in photovoltaic devices. This progress motivated us to develop a synthesis of colloidal FASnI₃ NCs with a concentration of Sn(IV) reduced to an insignificant level and to probe their intrinsic structural and optical properties. Intrinsic FASnI₃ NCs exhibit unusually low absorption coefficients of 4 × 10³ cm^-1 at the first excitonic transition, a 190 meV increase of the band gap as compared to the bulk material, and a lack of excitonic resonances. These features are attributed to a highly disordered lattice, distinct from the bulk FASnI₃ as supported by structural characterizations and first-principles calculations.

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.

Systematic investigation of metal dopants and mechanism for the SnO2 electron transport layer in perovskite solar cells

SnO₂, the most promising alternative to TiO₂ as the electron transport layer (ETL), has attracted great attention for perovskite solar cells (PSCs) due to its high bulk electron mobility, good band energy at the ETL/perovskite interface, and high chemical stability. To enable more efficient carrier transfer and extraction, elemental doping with different metal cations has been studied in SnO₂ ETLs. However, the systematic investigation of the doping mechanism lag far behind their efficiency promotion. In this paper, elements of the same main group (Li, Na, K) and period (K, Ca, Ga) have been selected for doping in SnO₂. The results showed that among the properties of the dopants, the electronegativity has the greatest influence. The smaller the electronegativity of the doping species, the more conducive it is to carrier transmission and separation. The corresponding mechanism was proposed and discussed. At last, an efficiency of 20.92% of PSCs based on SnO₂-K was achieved. In addition, the doped SnO₂ is more beneficial for the growth of perovskite crystals, thus reducing grain boundaries and enhancing the stability of the device.

A trifunctional polyethylene oxide buffer layer for stable and efficient all-inorganic CsPbBr3 perovskite solar cells

Carbon-based all-inorganic perovskite solar cells have attracted growing interest owing to their simple fabrication process, low cost, and high stability in air. On account of the large interfacial energy barriers and polycrystalline features of perovskite films, the carrier interface recombination and inherent defects in the perovskite layer are still great challenges in further increasing the power conversion efficiency and stability of carbon-based PSCs. We present here a trifunctional polyethylene oxide buffer layer at the perovskite/carbon interface to promote the PCE and stability of carbon-based all-inorganic CsPbBr₃ PSCs: (i) the PEO layer increases the crystallinity of inorganic CsPbBr₃ grains for low defect state density; (ii) the oxygenic groups in PEO chains passivate the defects on the perovskite surface; and (iii) the long hydrophobic alkyl chains improve the stability in moisture. The best encapsulated PSC achieves a PCE of 8.84% and maintains 84.8% of its initial efficiency in air with 80% RH over 30 days.

Multidentate Molecule Anchoring Halide Perovskite Surface and Regulating Crystallization Kinetics toward Efficient Light-Emitting Diodes

Functional passivators are conventionally utilized in modifying the crystallization properties of perovskites to minimize the non-radiative recombination losses in perovskite light-emitting diodes (PeLEDs). However, the weak anchor ability of some commonly adopted molecules has limited passivation ability to perovskites and even may desorb from the passivated defects in a short period of time, which bring about plenty of challenges for further development of high-performance PeLEDs. Here, a multidentate molecule, formamidine sulfinic acid (FSA), is introduced as a novel passivator to perovskites. FSA has multifunctional groups (S≐O, C≐N and NH₂ ) where the S≐O and C≐N groups enable coordination with the lead ions and the NH₂ interacts with the bromide ions, thus providing the most effective chemical passivation for defects and in turn the formation of highly stable perovskite emitters. Moreover, the interaction between the FSA and octahedral [PbBr₆ ]^4- can inhibit the formation of unfavorable low-n domains to further minimize the inefficient energy transfer inside the perovskite emitters. Therefore, the FSA passivated green-emitting PeLED exhibits a high external quantum efficiency (EQE) of 26.5% with fourfold enhancement in operating lifetime as compared to the control device, consolidating that the multidentate molecule is a promising strategy to effectively and sustainably passivate the perovskites.

Toward Efficient Two-Photon Circularly Polarized Light Detection through Cooperative Strategies in Chiral Quasi-2D Perovskites

Organic-inorganic hybrid perovskites carry unique semiconducting properties and advanced flexible crystal structures. These characteristics of organic-inorganic hybrid perovskites create a promising candidacy for circularly polarized light (CPL) detection. However, CPL detections based on chiral perovskites are limited to UV and visible wavelengths. The natural quantum well structures of layered hybrid perovskites generate strong light-matter interactions. This makes it possible to achieve near-infrared (NIR) CPL detection via two-photon absorption in the sub-wavelength region. In this study, cooperative strategies of dimension increase and mixed spacer cations are used to obtain a pair of chiral multilayered perovskites (R-β-MPA)EA₂ Pb₂ Br₇ and (S-β-MPA)EA₂ Pb₂ Br₇ (MPA = methylphenethylammonium and EA = ethylammonium). The distinctive bi-cations interlayer and multilayered inorganic skeletons provide enhanced photoconduction. Moreover, superior photoconduction leads to the prominent NIR CPL response with a responsivity up to 8.1 × 10^-5 A W^-1 . It is anticipated that this work can serve as a benchmark for the fabrication and optimization of efficient NIR CPL detection by simple chemical design.

Reexamining the Post-Treatment Effects on Perovskite Solar Cells: Passivation and Chloride Redistribution

Post-treatment is an essential passivation step for the state-of-the-art perovskite solar cells (PSCs) but the additional role is not yet exploited. In this work, perovskite film is fabricated under ambient air with wide humidity window and identify that chloride redistribution induced by post-treatment plays an important role in high performance. The chlorine/iodine ratio on the perovskite surface increases from 0.037 to 0.439 after cyclohexylmethylammonium iodide (CHMAI) treatment and the PSCs deliver a champion power conversion efficiency (PCE) of 24.42% (certificated 23.60%). The maximum external quantum efficiency of electroluminescence (EQE_EL ) reaches to 10.84% with a radiance of 170 W sr^-1  m^-2 , forming the reciprocity relation between EQE_EL and nonradiative open-circuit voltage loss (86.0 mV). After thermal annealing, 2D component of perovskite will increase while chloride decline, leading to improved photovoltage but reduced fill factor. Hence, it distinguishes that chloride enrichment can improve charge transport/recombination simultaneously and 2D passivation can suppress the nonradiative recombination. Moreover, CHMAI can leverage their roles in charge transport/recombination for better performance than phenylethylammonium iodide (Cl/I = 0.114, PCE = 23.32%), due to the stronger binding energy of Cl^- . This work provides the insight that the chloride fixation can improve the photovoltaic performance.

Fullerene-Liquid-Crystal-Induced Micrometer-Scale Charge-Carrier Diffusion in Organic Bulk Heterojunction

The short charge-carrier diffusion length (L_D ) (100-300 nm) in organic bulk heterojunction (BHJ) impedes the further improvement in power conversion efficiency (PCE) of organic solar cells (OSCs), especially for thick-film (>400 nm) devices matching with industrial solution processing. Here a facile method is developed to efficiently increase L_D and then improve PCEs of OSCs via introducing a fullerene liquid crystal, F1, into the active layer. F1 combines the inherent high electron mobility of fullerene and strong self-assembly capacity of liquid crystal, providing a fast channel for charge-carrier transport and reducing energetic disorder and trap density in BHJ film via enhancing crystallization. Typically, in PM6:Y6:F1 BHJ, the enhanced charge-carrier mobility (>10^-2 cm^-2 V^-1 s^-1 ) and prolonged charge-carrier lifetime (55.3 µs) are acquired to realize the record L_D of 1.6 or 2.4 µm for electron or hole, respectively, which are much higher than those of the PM6:Y6 binary sample and comparable to or even better than those values reported for some inorganic/hybrid materials, such as CuIn_x Ga_{(1- x )} Se₂ (CIGS) and perovskite thin films. Benefitting from the micrometer-scale L_D , the PM6:Y6:F1 ternary OSCs sustain a remarkable PCE of 15.23% with the active layer thickness approaching 500 nm.

UV-VIS-NIR broadband flexible photodetector based on layered lead-free organic-inorganic hybrid perovskite

The flexible photodetector is viewed as a research hotspot for numerous advanced optoelectronic applications. Recent progress has manifested that lead-free layered organic-inorganic hybrid perovskites (OIHPs) are highly attractive to engineering flexible photodetectors due to the effective overlapping of several unique properties, including efficient optoelectronic characteristics, exceptional structural flexibility, and the absence of Pb toxicity to humans and the environment. The narrow spectral response of most flexible photodetectors with lead-free perovskites is still a big challenge to practical applications. In this work, we demonstrate the flexible photodetector based on a novel (to our knowledge) narrow-bandgap OIHP of (BA)₂(MA)Sn₂I₇, with achieving a broadband response across an ultraviolet-visible-near infrared (UV-VIS-NIR) region as 365-1064 nm. The high responsivities of 28.4 and 2.0 × 10^-2 A/W are obtained at 365 and 1064 nm, respectively, corresponding to detectives of 2.3 × 10¹⁰ and 1.8 × 10⁷ Jones. This device also shows remarkable photocurrent stability after 1000 bending cycles. Our work indicates the huge application prospect of Sn-based lead-free perovskites in high-performance and eco-friendly flexible devices.

Intrinsic defects at the interface of the FAPbI3/MAPbI3 superlattice: insight from first-principles calculations

The use of a superlattice structure is an effective strategy to develop novel perovskites and obtain excellent light-absorbing materials. Based on first-principles calculations, we systematically studied the properties of intrinsic point defects at the interface of the FAPbI₃/MAPbI₃ superlattice. Our calculations show that charged defects are easier to form as compared to neutral ones at the superlattice interface due to low formation energies. Most defects with low formation energies have a shallow level in the band gap, and some deep level defects have high formation energies, so the superlattice perovskite exhibits high defect tolerance. Pb_I³⁺ is a dominant and detrimental defect, which acts as a non-radiative recombination center because it has low formation energy and a deep transition level. To avoid the generation of Pb_I³⁺ defects, it is suggested to synthesize FAPbI₃/MAPbI₃ superlattices under I-rich conditions. The calculated light absorption coefficients and photovoltaic performance parameters demonstrate that the presence of defects leads to a certain degree of reduction in light absorption and power conversion efficiency (PCE) of solar cells made of FAPbI₃/MAPbI₃ superlattices, but the excellent performance of the perovskite solar cell (PSC) is basically retained. The superlattice perovskites are still promising candidates for light-absorbing materials of PSCs. This study is expected to contribute to a better understanding of the properties of defects at the superlattice interface and provide theoretical support for the design of high performance PSCs.

Nanomaterial-Based Synaptic Optoelectronic Devices for In-Sensor Preprocessing of Image Data

With the advance in information technologies involving machine vision applications, the demand for energy- and time-efficient acquisition, transfer, and processing of a large amount of image data has rapidly increased. However, current architectures of the machine vision system have inherent limitations in terms of power consumption and data latency owing to the physical isolation of image sensors and processors. Meanwhile, synaptic optoelectronic devices that exhibit photoresponse similar to the behaviors of the human synapse enable in-sensor preprocessing, which makes the front-end part of the image recognition process more efficient. Herein, we review recent progress in the development of synaptic optoelectronic devices using functional nanomaterials and their unique interfacial characteristics. First, we provide an overview of representative functional nanomaterials and device configurations for the synaptic optoelectronic devices. Then, we discuss the underlying physics of each nanomaterial in the synaptic optoelectronic device and explain related device characteristics that allow for the in-sensor preprocessing. We also discuss advantages achieved by the application of the synaptic optoelectronic devices to image preprocessing, such as contrast enhancement and image filtering. Finally, we conclude this review and present a short prospect.

Recent advances of two-dimensional material additives in hybrid perovskite solar cells

Perovskite solar cells (PSCs) have become one of the state-of-the-art photovoltaic technologies due to their facile solution-based fabrication processes combined with extremely high photovoltaic performance originating from excellent optoelectronic properties such as strong light absorption, high charge mobility, long free charge carrier diffusion length, and tunable direct bandgap. However, the poor intrinsic stability of hybrid perovskites under environmental stresses including light, heat, and moisture, which is often associated with high defect density in the perovskite, has limited the large-scale commercialization and deployment of PSCs. The use of process additives, which can be included in various subcomponent layers in the PSC, has been identified as one of the effective approaches that can address these issues and improve the photovoltaic performance. Among various additives that have been explored, two-dimensional (2D) materials have emerged recently due to their unique structures and properties that can enhance the photovoltaic performance and device stability by improving perovskite crystallization, defect passivation, and charge transport. Here, we provide a review of the recent progresses in 2D material additives for improving the PSC performance based on key representative 2D material systems, including graphene and its derivatives, transitional metal dichalcogenides, and black phosphorous, providing a useful guideline for further exploiting unique nanomaterial additives for more efficient and stable PSCs in the near future.

Universal Molecular Control Strategy for Scalable Fabrication of Perovskite Light-Emitting Diodes

Despite the rapid progress in perovskite light-emitting diodes (PeLEDs), the electroluminescence performance of large-area perovskite devices lags far behind that of laboratory-size ones. Here, we report a 3.5 cm × 3.5 cm large-area PeLED with a record-high external quantum efficiency of 12.1% by creating an amphipathic molecular interface modifier of betaine citrate (BC) between the perovskite layer and the underlying hole transport layer (HTL). It is found that the surface wettability for various HTLs can be efficiently improved as a result of the coexistence of methyl and carboxyl groups in the BC molecules that makes favorable groups to selectively contact with the HTL surface and increases the surface free energy, which greatly facilitates the scalable process of solution-processed perovskite films. Moreover, the luminous performance of perovskite emitters is simultaneously enhanced through the coordination between C═O in the carboxyl groups and Pb dangling bonds.

Recent Development of Halide Perovskite Materials and Devices for Ionizing Radiation Detection

Ionizing radiation such as X-rays and γ-rays has been extensively studied and used in various fields such as medical imaging, radiographic nondestructive testing, nuclear defense, homeland security, and scientific research. Therefore, the detection of such high-energy radiation with high-sensitivity and low-cost-based materials and devices is highly important and desirable. Halide perovskites have emerged as promising candidates for radiation detection due to the large light absorption coefficient, large resistivity, low leakage current, high mobility, and simplicity in synthesis and processing as compared with commercial silicon (Si) and amorphous selenium (a-Se). In this review, we provide an extensive overview of current progress in terms of materials development and corresponding device architectures for radiation detection. We discuss the properties of a plethora of reported compounds involving organic-inorganic hybrid, all-inorganic, all-organic perovskite and antiperovskite structures, as well as the continuous breakthroughs in device architectures, performance, and environmental stability. We focus on the critical advancements of the field in the past few years and we provide valuable insight for the development of next-generation materials and devices for radiation detection and imaging applications.

Perylene Monoimide Phosphorus Salt Interfacial Modified Crystallization for Highly Efficient and Stable Perovskite Solar Cells

Reducing the interfacial defects of perovskite films is key to improving the performance of perovskite solar cells (PSCs). In this study, two kinds of perylene monoimide (PMI) derivative phosphonium bromide salts were designed and used as a multifunctional interface-modified layer in PSCs. These two molecules are inserted between SnO₂ and perovskite to produce a bidirectional passivation effect. The interaction with SnO₂ reduces the oxygen vacancy on the surface of SnO₂ and tunes the energy level of the electron transport layer, making more matches with the perovskite layer. The modified layer can promote the growth of perovskite crystals and reduce the interfacial defects of the perovskite film. Furthermore, the power conversion efficiency (PCE) of PSCs increased from 19.49 to 22.85%, and the open-circuit voltage (V_OC) increased from 1.06 to 1.14 V. At the same time, the PCE of the SnO₂/PMI-TPP-based device remained 88% of the initial PCE after 240 h of continuous illumination. In addition, these two PMI derivatives with a quasi-planar structure can improve the flexibility of flexible PSCs. This study provided a new strategy for the interfacial modification of PSCs and a new insight into the application of flexible PSCs.

Synergistic Effect of Surface p-Doping and Passivation Improves the Efficiency, Stability, and Reduces Lead Leakage in All-Inorganic CsPbIBr2 -Based Perovskite Solar Cells

Wide-bandgap inorganic cesium lead halide CsPbIBr₂ is a popular optoelectronic material that researchers are interested in because of the character that balances the power conversion efficiency and stability of solar cells. It also has great potential in semitransparent solar cells, indoor photovoltaics, and as a subcell for tandem solar cells. Although CsPbIBr₂ -based devices have achieved good performance, the open-circuit voltage (V_oc ) of CsPbIBr₂ -based perovskite solar cells (PSCs) is still lower, and it is critical to further reduce large energy losses (E_loss ). Herein, a strategy is proposed for achieving surface p-type doping for CsPbIBr₂ -based perovskite for the first time, using 1,5-Diaminopentane dihydroiodide at the perovskite surface to improve hole extraction efficiency. Meanwhile, the adjusted energy levels reduce E_loss and improve V_oc of the CsPbIBr₂ PSCs. Furthermore, the Cs- and Br-vacancies at the interface are filled, reducing structural disorder and defect states and thus improving the quality of the perovskite film. As a result, the target device achieves a high efficiency of 11.02% with a V_oc of 1.33 V, which is among the best values. In addition to the improved performance, the stability of the target device under various conditions is enhanced, and the lead leakage is effectively suppressed.

Honeycomb-Type TiO2 Films Toward a High Tolerance to Optical Paths for Perovskite Solar Cells

Given the advantages of high power conversion efficiencies (PCEs), antisolvent-step free production, and suitability for device production in ambient conditions, perovskite solar cells (PSCs) based on ionic-liquid solvents have attained particular research interest. To further improve device performance, light management could be optimized to increase light harvesting in the perovskite layer. Here, ordered honeycomb-like TiO₂ (Hc-TiO₂ ) structures with a periodicity of around 450 nm were fabricated through a sacrificial template method. With this photonic crystal structure, the control to light flow and the confinement effect for perovskite growth were achieved simultaneously in the Hc-TiO₂ , leading to improved light absorption as well as preferred crystal orientation. Furthermore, a reduced trap-state density and a well-aligned energy level induced by the perovskite/pore interlayer facilitated the charge-carrier extraction from the perovskite layer to electron transport layer. As a result, the structured devices performed better than the planar cells. And the angular dependent J-V sweeps show that the structured device reserved 76 % of its initial short circuit current density (J_sc ), whereas the planar cell showed more than a half loss under the incident light of 40°, demonstrating a reduced downward trend in J_sc with the presence of photonic crystal structures. This occurrence also suggests that the structured PSCs in this work have a high tolerance to optical path changes.

Improved Defect Tolerance and Charge Carrier Lifetime in Tin-Lead Mixed Perovskites: Ab Initio Quantum Dynamics

Simulations by nonadiabatic (NA) molecular dynamics demonstrate that mixing tin with lead in CH₃NH₃PbI₃ can passivate the midgap state created by an interstitial iodine (I_i) via the imposed compressive strain and upshifted valence band maximum, reduce NA coupling by decreasing electron-hole wave functions overlap, and shortens pure-dephasing time by introducing high-frequency phonon modes. Thus, the charge carrier lifetime extends to 3.6 ns due to the significantly reduced nonradiative electron-hole recombination, which is an order of magnitude longer than the I_i-containing CH₃NH₃PbI₃, over 2.5 times longer than the pristine CH₃NH₃PbI₃ (1.4 ns), and even 1.7 times longer than the tin-lead mixed perovskite without the I_i defects (2.1 ns). Tin-lead alloying simultaneously increases the I_i defect formation energy to 0.402 eV from 0.179 eV in CH₃NH₃PbI₃, which effectively enhances defect tolerance by reducing the defect concentration. The study reveals the factors controlling the enhanced performance of tin-lead mixed perovskite solar cells.

Supermolecule-assisted synthesis of perovskite nanorods with high PLQY for standard blue emission

We fabricated CsPbBr₃ nanorods with standard blue emission (462 nm) and a high PLQY of ∼90% with the assistance of supermolecules. The β-CD works as a co-ligand and confine the isotropic growth of the nanocrystals to produce anisotropic nanorods. The strong coordination between β-CD and Pb favors the improvement of the PLQY and stability.

Role of inorganic cations in the excitonic properties of lead halide perovskites

We theoretically investigate lead iodide perovskites of general formula APbI₃ for a series of metallic cations (namely Cs⁺, Rb⁺, K⁺, Na⁺ and Li⁺) by means of density functional theory, the GW method and the Bethe-Salpeter equation including spin-orbit coupling. We demonstrate that the low-energy edges (up to 1.3 eV) of the absorption spectra are dominated by weakly bound excitons, with binding energies E_b of ∼ 30-80 meV, and the corresponding intensities increase as metallic cations become lighter. The middle parts of the spectra (1.8-2.4 eV), on the other hand, contain optical dipole transitions comprising more confined excitons (E_b ∼ 150-200 meV) located at PbI₃. These parts of the spectra correspond to the optical-gain wavelengths which are experimentally achieved in optically pumped perovskite lasers. Finally, the higher energy parts, from about 2.8 eV (LiPbI₃) to 4.3 eV (CsPbI₃), contain optical transitions with very confined excitons (E_b ∼ 220-290 meV) located at halide atoms and the empty states of the metallic cations.

Non-preheating fabricated semitransparent quasi-2D perovskite solar cells

Although the hot-casting (HC) method can obtain efficient quasi-2D perovskite solar cells, this method cannot effectively control the uniformity of the thin film, and the high preheating substrate temperature will also form low n perovskite phases (n = 2) at the interface, which is not conducive to the transport of carriers. Semitransparent solar cells have great application prospects in building-integrated photovoltaic and tandem devices. Herein, a non-preheating (NP) film-casting method is proposed to realize a highly uniform and phase controllable quasi-2D perovskite film (BA₂MA₃Pb₄I₁₃, BA⁺:C₄H₁₁NH₃⁺, MA⁺:CH₃NH₃⁺). As a result, the NP-processed film gets the highest light utilization efficiency (LUE = 4.01%) for semitransparent quasi-2D perovskite solar cells (ST-Quasi-2D-PSCs) with power conversion efficiency (PCE) of 9.60%, average visible transmittance (AVT) of 41.73%, good bifaciality factor, high LUE in low light intensity and good stability.

Synthetic approaches for perovskite thin films and single-crystals

Halide perovskites are compelling candidates for the next generation of photovoltaic technologies owing to an unprecedented increase in power conversion efficiency and their low cost, facile fabrication and outstanding semiconductor properties.

Intermediate-phase engineering via dimethylammonium cation additive for stable perovskite solar cells

Achieving the long-term stability of perovskite solar cells is arguably the most important challenge required to enable widespread commercialization. Understanding the perovskite crystallization process and its direct impact on device stability is critical to achieving this goal. The commonly employed dimethyl-formamide/dimethyl-sulfoxide solvent preparation method results in a poor crystal quality and microstructure of the polycrystalline perovskite films. In this work, we introduce a high-temperature dimethyl-sulfoxide-free processing method that utilizes dimethylammonium chloride as an additive to control the perovskite intermediate precursor phases. By controlling the crystallization sequence, we tune the grain size, texturing, orientation (corner-up versus face-up) and crystallinity of the formamidinium (FA)/caesium (FA)_yCs_1-yPb(I_xBr_1-x)₃ perovskite system. A population of encapsulated devices showed improved operational stability, with a median T80 lifetime (the time over which the device power conversion efficiency decreases to 80% of its initial value) for the steady-state power conversion efficiency of 1,190 hours, and a champion device showed a T80 of 1,410 hours, under simulated sunlight at 65 °C in air, under open-circuit conditions. This work highlights the importance of material quality in achieving the long-term operational stability of perovskite optoelectronic devices.

Unravelling the Interfacial Dynamics of Bandgap Funneling in Bismuth-Based Halide Perovskites

An environmentally friendly mixed-halide perovskite MA₃ Bi₂ Cl_{9- x} I_x with a bandgap funnel structure has been developed. However, the dynamic interfacial interactions of bandgap funneling in MA₃ Bi₂ Cl_{9- x} I_x perovskites in the photoelectrochemical (PEC) system remain ambiguous. In light of this, single- and mixed-halide lead-free bismuth-based hybrid perovskites-MA₃ Bi₂ Cl_{9- y} I_y and MA₃ Bi₂ I₉ (named MBCl-I and MBI)-in the presence and absence of the bandgap funnel structure, respectively, are prepared. Using temperature-dependent transient photoluminescence and electrochemical voltammetric techniques, the photophysical and (photo)electrochemical phenomena of solid-solid and solid-liquid interfaces for MBCl-I and MBI halide perovskites are therefore confirmed. Concerning the mixed-halide hybrid perovskites MBCl-I with a bandgap funnel structure, stronger electronic coupling arising from an enhanced overlap of electronic wavefunctions results in more efficient exciton transport. Besides, MBCl-I's effective diffusion coefficient and electron-transfer rate demonstrate efficient heterogeneous charge transfer at the solid-liquid interface, generating improved photoelectrochemical hydrogen production. Consequently, this combination of photophysical and electrochemical techniques opens up an avenue to explore the intrinsic and interfacial properties of semiconductor materials for elucidating the correlation between material characterization and device performance.

Continuous Modification of Perovskite Film by a Eu Complex to Fabricate the Thermal and UV-Light-Stable Solar Cells

Perovskite solar cells (PSCs) with simple and low-cost processability have shown promising photovoltaic performances. However, internal defects, external UV light, and heat sensitivity are principal obstacles on their way toward commercialization. Herein, we prepare an Eu complex and directly dope it into the perovskite precursor as a UV filter to decrease the photodegradation of PSCs. The formation of hydrogen bonds between the organic cation of perovskite and the -CF₃ in the Eu complex could restrain the escape of organic cations under heating. The Eu complex acts as a redox shuttle to reduce metallic lead (Pb⁰) and iodine (I⁰) defects when the PSCs have a long-time operation. Additionally, the ligand-containing aromatic rings could reduce the trace amount of I⁰ existing as electronic defects in perovskites and together with the long alkyl chain retard the moisture immersion into the PSCs. The best efficiency of PSCs modified by the Eu complex improves up to 20.9%. The excellent thermal stability and UV-light resistance are also realized. This strategy provides a method to design a passivator which continuously modifies the imperfections and inhibits the chemical chain reactions in perovskite film, thereby enhancing the performance and stability of PSCs.

Caution! Static Supercell Calculations of Defect Migration in Higher Symmetry ABX3 Perovskite Halides May Be Unreliable: A Case Study of Methylammonium Lead Iodide

Activation energies of defect migration in ABX₃ perovskite halides are widely obtained through static supercell calculations with the nudged-elastic-band method. Taking methylammonium lead iodide (CH₃NH₃PbI₃, MAPbI₃) as an example, we demonstrate that such calculations are unreliable for the higher symmetry structures adopted by the material at temperatures relevant to device operation (tetragonal and cubic MAPbI₃) because, in addition to ion relaxation around the point defects, local structural modifications characteristic of the ground-state (orthorhombic) structure occur. In this way, we offer a simple explanation of why calculated activation energies of defect migration in MAPbI₃ suffer from surprisingly large scatter. We propose a robust test to determine whether static supercell calculations of point-defect processes in ABX₃ perovskite systems are reliable.

First-principles structural, elastic and optoelectronics study of sodium niobate and tantalate perovskites

The intensified quest for efficient materials drives us to study the alkali (Na)-based niobate (NaNbO₃) and tantalate (NaTaO₃) perovskites while exploiting the first-principles approach based on density functional theory, coded within WIEN2K. While using the Birch Murnaghan fit, we find these materials to be stable structurally. Similarly, the ab-initio molecular dynamics simulations (AIMD) at room temperature reveals that the compounds exhibit no structural distortion and are stable at room temperature. By using the recommended modified Becke-Johnson potential, we determine the electronic characteristics of the present materials providing insight into their nature: they are revealed to be indirect semiconductors with the calculated bandgaps of 2.5 and 3.8 eV for NaNbO₃ and NaTaO₃, respectively. We also determine the total and partial density of states for both materials and the results obtained for the bandgap energies of these materials are consistent with those determined by the band structure. We find that both compounds exhibit transparency to the striking photon at low energy and demonstrate absorption and optical conduction in the UV region. The elastic study shows that these compounds are mechanically stable, whereas NaNbO₃ exhibits stronger ability to withstand compressive as well as shear stresses and resists change in shape while NaTaO₃ demonstrates weaker ability to resist change in volume. We also find that none of the compound is perfectly isotropic and NaNbO₃ and NaTaO₃ are ductile and brittle in nature, respectively. By studying the optical properties of these materials, we infer that they are promising candidates for applications in optoelectronic devices. We believe that this report will invoke the experimental studies for further investigation.

Bulk Heterostructure BA2PbI4/MAPbI3 Perovskites for Suppressed Ion Migration To Achieve Sensitive X-ray Detection Performance

Three-dimensional (3D) lead-halide perovskites with outstanding mobility-lifetime products and large attenuation coefficients for X-ray photons have demonstrated highly sensitive X-ray detection. However, there exists severe ion migration, especially under electrical bias, that results in dark-current drift and poorer device stability. Theoretical analyses suggest that 3D perovskites with two-dimensional (2D) perovskites may mitigate ion migration and reduce the dark current to achieve a drastically lower detection limit, which is badly needed for X-ray diagnostics. A bulk 2D/3D perovskite heterostructure is therefore designed and prepared by hot-pressing a mixture of BA₂PbI₄ and MAPbI₃ particles. Compared with the pure MAPbI₃ pellet, the bulk 2D/3D heterostructure pellet shows much higher resistivity, hence, significantly reduced ion migration and a much smaller dark-current drift of 4.84 × 10^-5 nA cm^-1 s^-1 V^-1, which is much lower than that of the pristine MAPbI₃ pellet, thus demonstrating its effectiveness for the suppression of ion migration. The bulk 2D/3D heterostructure pellet attains an X-ray sensitivity of 2.0 × 10³ μC Gy_air^-1 cm^-2 as well as a lower detection limit of 111.76 nGy s^-1 under 10 V bias. This work provides a successful strategy to prepare X-ray detectors with suppressed ion migration and negligible dark current drift, which will further benefit the development of lead-halide perovskite X-ray detectors.

High efficiency pure blue perovskite quantum dot light-emitting diodes based on formamidinium manipulating carrier dynamics and electron state filling

Achieving high efficiency and stable pure blue colloidal perovskite quantum dot (QD) light-emitting diodes (LEDs) is still an enormous challenge because blue emitters typically exhibit high defect density, low photoluminescence quantum yield (PLQY) and easy phase dissociation. Herein, an organic cation composition modification strategy is used to synthesize high-performance pure blue perovskite quantum dots at room temperature. The synthesized FA-CsPb(Cl0.5Br0.5)3 QDs show a bright photoluminescence with a high PLQY (65%), which is 6 times higher than the undoped samples. In addition, the photophysical properties of the FA cation doping was deeply illustrated through carrier dynamics and first principal calculation, which show lower defects, longer lifetime, and more reasonable band gap structure than undoped emitters. Consequently, pure blue FA-CsPb(Cl0.5Br0.5)3 QDs light-emitting devices were fabricated and presented a maximum luminance of 1452 cd m-2, and an external quantum efficiency of 5.01 % with an emission at 474 nm. The excellent photoelectric properties mainly originate from the enhanced blue QDs emitter and effective charge injection and exciton radiation. Our finding underscores this easy and feasible room temperature doping approach as an alternative strategy to blue perovskite QD LED development.

Chemical approaches for electronic doping in photovoltaic materials beyond crystalline silicon

Electronic doping is applied to tailor the electrical and optoelectronic properties of semiconductors, which have been widely adopted in information and clean energy technologies, like integrated circuit fabrication and PVs. Though this concept has prevailed in conventional PVs, it has achieved limited success in the new-generation PV materials, particularly in halide perovskites, owing to their soft lattice nature and self-compensation by intrinsic defects. In this review, we summarize the evolution of the theoretical understanding and strategies of electronic doping from Si-based photovoltaics to thin-film technologies, e.g., GaAs, CdTe and Cu(In,Ga)Se₂, and also cover the emerging PVs including halide perovskites and organic solar cells. We focus on the chemical approaches to electronic doping, emphasizing various chemical interactions/bonding throughout materials synthesis/modification to device fabrication/operation. Furthermore, we propose new classifications and models of electronic doping based on the physical and chemical properties of dopants, in the context of solid-state chemistry, which inspires further development of optoelectronics based on perovskites and other hybrid materials. Finally, we outline the effects of electronic doping in semiconducting materials and highlight the challenges that need to be overcome for reliable and controllable doping.

Ultra-stable blue-emitting lead-free double perovskite Cs2SnCl6 nanocrystals enabled by an aqueous synthesis on a microfluidic platform

Blue emitting Sn-based lead-free halide perovskite nanocrystals (NCs) are considered to be a promising material in lighting and displays. However, industrialised fabrication of blue-emitting NCs still remains a significant challenge due to the use of toxic solvents and optical instability, not mentioning in large-scale synthesis. In this work, a green-route synthesis of blue-emitting lead-free halide perovskite Cs₂SnCl₆ powders is developed, in which deionized water with a small amount of inorganic acid is used as the solvent and the synthesis of the Cs₂SnCl₆ powders is achieved on a microfluidic platform. Using the Cs₂SnCl₆ powders, we prepare Cs₂SnCl₆ NCs via an ultrasonication process. Changing the volume ratio of the ligands (oleic acid to oleylamine) can alter the photoluminescence (PL) characteristics of the prepared NCs, including the PL-peak wavelength, PL-peak intensity and quantum yield. The highest photoluminescence quantum yield (PLQY) of 13.4% is achieved by the Cs₂SnCl₆ NCs prepared with the volume ratio of oleic acid to oleylamine of 40 μL to 10 μL. A long-term PL stability test demonstrates that the as-synthesized Cs₂SnCl₆ NCs can retain a stable PLQY over a period of 60 days. This work opens up a new path for a large-scale green-route synthesis of blue-emitting Sn-based lead-free NCs, such as Cs₂SnX₆ (Cl, Br and I), towards their applications in optoelectronics.

Zero-Dimensional Cs3BiX6 (X = Br, Cl) Single Crystal Films with Second Harmonic Generation

The development of atomically thin single crystal films is necessary to potential applications in the 2D semiconductor field, and it is significant to explore new physical properties in low-dimensional semiconductors. Since, zero-dimensional (0D) materials without natural layering are connected by strong chemical bonds, it is challengeable to break symmetry and grow 0D Cs₃BiX₆ (X = Br, Cl) single crystal thin films. Here, we report the successful growth of 0D Cs₃BiX₆ (X = Br, Cl) single crystal films using a solvent evaporation crystallization strategy. Their phases and structures are both well evaluated to confirm 0D Cs₃BiX₆ (X = Br, Cl) single crystal films. Remarkably, the chemical potential dependent morphology evolution phenomenon is observed. It gives rise to morphology changes of Cs₃BiBr₆ films from rhombus to hexagon as BiBr₃ concentration increased. Additionally, the robust second harmonic generation signal is detected in the Cs₃BiBr₆ single crystal film, demonstrating the broken symmetry originated from decreased dimension or shape change.

Blue Perovskite Nanocrystal Light-Emitting Diodes: Overcoming RuddlesdenPopper Fault-Induced Nonradiative Recombination via Post-Halide Exchange

Metal halide perovskites (MHPs) have gained traction as emitters owing to their excellent optical properties, such as facile bandgap tuning, defect tolerance, and high color purity. Nevertheless, blue-emitting MHP light-emitting diodes (LEDs) show only marginal progress in device efficiency compared with green and red LEDs. Herein, the origin of the drop in efficiency of blue-emitting perovskite nanocrystals (PNCs) by mixing halides and the genesis of Ruddlesden-Popper faults (RPFs) in CsPbBr_X Cl_3-X nanocrystals is investigated. Using scanning transmission electron microscopy and density functional theory calculations, the authors have found that RPFs induce possible nonradiative recombination pathways owing to the high chloride vacancy concentration nearby. The authors further confirm that the blue-emitting PNCs do not show RPFs post-halide exchange in the CsPbBr₃ nanocrystals. By introducing the post-halide exchange treatment, high-efficiency pure blue-emitting (464 nm) PNC-based LEDs with an external quantum efficiency of 2.1% and excellent spectral stability with a full-width at half-maximum of 14 nm are obtained.

Halide Perovskite: A Promising Candidate for Next-Generation X-Ray Detectors

In the past decade, metal halide perovskite (HP) has become a superstar semiconductor material due to its great application potential in the photovoltaic and photoelectric fields. In fact, HP initially attracted worldwide attention because of its excellent photovoltaic efficiency. However, HP and its derivatives also show great promise in X-ray detection due to their strong X-ray absorption, high bulk resistivity, suitable optical bandgap, and compatibility with integrated circuits. In this review, the basic working principles and modes of both the direct-type and the indirect-type X-ray detectors are first summarized before discussing the applicability of HP for these two types of detection based on the pros and cons of different perovskites. Furthermore, the authors expand their view to different preparation methods developed for HP including single crystals and polycrystalline materials. Upon systematically analyzing their potential for X-ray detection and photoelectronic characteristics on the basis of different structures and dimensions (0D, 2D, and 3D), recent progress of HPs (mainly polycrystalline) applied to flexible X-ray detection are reviewed, and their practicability and feasibility are discussed. Finally, by reviewing the current research on HP-based X-ray detection, the challenges in this field are identified, and the main directions and prospects of future research are suggested.

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.

Conformal Imidazolium 1D Perovskite Capping Layer Stabilized 3D Perovskite Films for Efficient Solar Modules

Although the perovskite solar cells have been developed rapidly, the industrialization of perovskite photovoltaics is still facing challenges, especially considering their stability issues. Here, the new type of benzimidazolium salt, N,N'-dialkylbenzimidazolium iodide, is proposed and functionalized to convert the three-dimensional (3D) FACs-perovskite films into one-dimensional (1D) capping layer topped 1D/3D structure either in individual device or module levels. This conformal interface modulation demonstrates that not only can effectively stabilize FACs-based perovskite films by inhibiting the lateral and vertical iodide diffusions in devices or modules, ensuring an excellent operation and environmental stability, but also provides an excellent charge transporting channel through the well-designed 1D crystal structure. Consequently, efficient device performance with power conversion efficiency up to 24.3% is readily achieved. And the large-area perovskite solar modules with high efficiency (19.6% for the active areas of 18 cm2 ) and long-term stability (about 500 h in AM 1.5G illumination or about 1000 h under double-85 conditions) are also successfully verified.

Molecularly Functionalized SnO2 Films by Carboxylic Acids for High-Performance Perovskite Solar Cells

Metal oxides are commonly employed as electron transport layers (ETLs) for n-i-p perovskite solar cells (PSCs), but the presence of surface traps and their mismatched energy alignment with perovskites limits the corresponding device performance. Therefore, the interfacial modification of ETLs by functional molecules becomes an important strategy for tailoring the interfacial properties and facilitating an efficient charge extraction and transport in PSCs. However, an in-depth understanding of the influences of their molecular structures on the surface chemistry and electronic properties of ETLs is rarely discussed. Herein, three carboxylic acid-based molecules with different chemical structures were employed to modify the SnO₂ ETL and their effects on the performance of PSCs were systematically investigated. We found that the alkyl-chain length and carboxyl number in molecular structures can dramatically alter their binding strength to SnO₂, providing a good strategy to fine-tune their film quality, electron mobility, and energy offset at the cathode interface. Benefiting from the optimal coordination ability of citric acid (CA) to SnO₂, the corresponding PSCs show better charge transport properties and suppressed nonradiative recombination, leading to a champion efficiency of 23.1% with much improved environmental stability, highlighting the potential of rational design of molecular modifiers for high-performance ETLs applied in PSCs.

Organic-Inorganic Lead Halide Perovskite Single Crystal: From Synthesis to Applications

Organic-inorganic lead halide perovskite is widely used in the photoelectric field due to its excellent photoelectric characteristics. Among them, perovskite single crystals have attracted much attention due to its lower trap density and better carrier transport capacity than their corresponding polycrystalline materials. Owing to these characteristics, perovskite single crystals have been widely used in solar cells, photodetectors, light-emitting diode (LED), and so on, which have greater potential than polycrystals in a series of optoelectronic applications. However, the fabrication of single-crystal devices is limited by size, thickness, and interface problems, which makes the development of single-crystal devices inferior to polycrystalline devices, which also limits their future development. Here, several representative optoelectronic applications of perovskite single crystals are introduced, and some existing problems and challenges are discussed. Finally, we outlook the growth mechanism of single crystals and further the prospects of perovskite single crystals in the further field of microelectronics.