Overview of Inorganic Electrolytes for All-Solid-State Sodium Batteries

All-solid-state sodium batteries (AS3B) emerged as a strong contender in the global electrochemical energy storage market as a replacement for current lithium-ion batteries (LIB) owing to their high abundance, low cost, high safety, high energy density, and long calendar life. Inorganic electrolytes (IEs) are highly preferred over the conventional liquid and solid polymer electrolytes for sodium-ion batteries (SIBs) due to their high ionic conductivity (∼10-2-10-4 S cm-1), wide potential window (∼5 V), and overall better battery performances. This review discusses the bird's eye view of the recent progress in inorganic electrolytes such as Na-β"-alumina, NASICON, sulfides, antipervoskites, borohydride-type electrolytes, etc. for AS3Bs. Current state-of-the-art inorganic electrolytes in correlation with their ionic conduction mechanism present challenges and interfacial characteristics that have been critically reviewed in this review. The current challenges associated with the present battery configuration are overlooked, and also the chemical and electrochemical stabilities are emphasized. The substantial solution based on ongoing electrolyte development and promising modification strategies are also suggested.

Enhancing Surface Modification and Carrier Extraction in Inverted Perovskite Solar Cells via Self-Assembled Monolayers

Perovskite solar cells (PSCs) have been significantly improved by utilizing an inorganic hole-transporting layer (HTL), such as nickel oxide. Despite the promising properties, there are still limitations due to defects. Recently, research on self-assembled monolayers (SAMs) is being actively conducted, which shows promise in reducing defects and enhancing device performance. In this study, we successfully engineered a p-i-n perovskite solar cell structure utilizing HC-A1 and HC-A4 molecules. These SAM molecules were found to enhance the grain morphology and uniformity of the perovskite film, which are critical factors in determining optical properties and device performance. Notably, HC-A4 demonstrated superior performance due to its distinct hydrophilic properties with a contact angle of 50.3°, attributable to its unique functional groups. Overall, the HC-A4-applied film exhibited efficient carrier extraction properties, attaining a carrier lifetime of 117.33 ns. Furthermore, HC-A4 contributed to superior device performance, achieving the highest device efficiency of 20% and demonstrating outstanding thermal stability over 300 h.

Preparation of CH3NH3PbBr3 Perovskites Encapsulated in ZIF-8 with Improved Stability and Their Application in Fluorimetry and Information Encryption

Metal halide perovskites (MHPs) have been promising functional materials for developing solar cells, lasers, photodetectors, and sensors due to their outstanding optical and electrical characteristics. However, they suffer from very poor stability for their high sensitivity to some environmental factors such as temperature, UV irradiation, pH, and polar solvent, which limits their extensive practical applications. Herein, a derived metal organic framework material, Pb-ZIF-8, was prepared as a precursor via a doping protocol. Then, CH₃NH₃PbBr₃ perovskites encapsulated in ZIF-8 (CH₃NH₃PbBr₃@ZIF-8) with green fluorescent (FL) emission were synthesized via a facile in situ protocol by using the derived metal organic frameworks material as a source of Pb element. With the protection of encapsulated ZIF-8, the perovskites material shows good FL properties under various harsh environmental conditions, which facilitates facile application in various fields. To verify the practical application potential of CH₃NH₃PbBr₃@ZIF-8, we utilized them as FL probes to establish a highly sensitive method for detecting glutathione. Furthermore, the rapid conversion process from non-FL Pb-ZIF-8 to FL CH₃NH₃PbBr₃@ZIF-8 was utilized to realize encryption and decryption of confidential information. This work opens an avenue to the development of perovskites-based devices with greatly improved stability in harsh external environments.

Machine learning and density functional theory simulation of the electronic structural properties for novel quaternary semiconductors

In order to accelerate the application of quaternary optoelectronic materials in the field of luminescence, it is crucial to develop new quaternary semiconductor materials with excellent properties. However, faced with vast alternative quaternary semiconductors, traditional trial-and-error methods tend to be laborious and inefficient. Here, we combined machine learning (ML) with density functional theory (DFT) calculation to predict the bandgaps of 2180 quaternary semiconductors, most of which were undeveloped but environmentally friendly. The evaluation coefficient (R²) of the model using a random forest algorithm was up to 0.93 in ML. Four novel quaternary semiconductors with direct bandgaps: Ag₂InGaS₄, AgZn₂InS₄, Ag₂ZnSnS₄, and AgZn₂GaS₄, were selected from the ML model. Then their electronic structures and optical properties were further verified and studied by DFT calculations, which demonstrated that the four quaternary semiconductors had direct bandgaps, a small effective mass, and a large exciton binding energy and Stokes shift. Our calculation could significantly speed up the discovery of novel optoelectronic semiconductors and has a certain reference value for the study of luminescent materials and devices.

Upscaling of Carbon-Based Perovskite Solar Module

Perovskite solar cells (PSCs) and modules are driving the energy revolution in the coming photovoltaic field. In the last 10 years, PSCs reached efficiency close to the silicon photovoltaic technology by adopting low-cost solution processes. Despite this, the noble metal (such as gold and silver) used in PSCs as a counter electrode made these devices costly in terms of energy, CO2 footprint, and materials. Carbon-based perovskite solar cells (C-PSCs) and modules use graphite/carbon-black-based material as the counter electrode. The formulation of low-cost carbon-based inks and pastes makes them suitable for large area coating techniques and hence a solid technology for imminent industrialization. Here, we want to present the upscaling routes of carbon-counter-electrode-based module devices in terms of materials formulation, architectures, and manufacturing processes in order to give a clear vision of the scaling route and encourage the research in this green and sustainable direction.

Method to Inhibit Perovskite Solution Aging: Induced by Perovskite Microcrystals

The main feature of perovskite solar cells (PSCs) is that the perovskite layer can be fabricated by the solution method, while the long-time stability of the precursor solution is critical. During the fabrication of formamidinium (FA)-based PSCs, the introduction of methylammonium cations (MA⁺) in the precursor solution can accelerate the crystallization process of the perovskite layer, stabilize the perovskite structure, and passivate defects. However, MA⁺ is easy to deprotonate to generate MA molecules, and it then condensates with formamidinium iodide (FAI) to form adverse byproducts. Herein, perovskite microcrystals (MCs) for preparing perovskite precursor solution were investigated in details, which can improve the long-term stability of the precursor solution and the perovskite film. We found that FA⁺ in MC solution was confined in the three-dimensional scaffold, preventing it from reacting with MA⁺. Meanwhile, MCs can effectively promote nucleation to form large grains in perovskite films. The photoelectric conversion efficiency (PCE) of the device with 3 week-aged MC solution remains at 90% and is only reduced by 10% after 160 h of continuous operation, which far exceeds the performance of the PCE of those based on mixed monomer powder (MP) solution. Therefore, perovskite MCs, an effective reactive inhibitor to improve the stability of perovskite precursor solutions, are of great significance for large-scale commercial fabrication.

Bio-Inspired Graphitic Carbon-Based Large-Area (10 × 10 cm2) Perovskite Solar Cells: Stability Assessments under Indoor, Outdoor, and Water-Soaked Conditions

In the emerging photovoltaic (PV) technologies, the golden triangle rule includes higher efficiency, longevity (or stability), and low cost, which are the foremost criteria for the root of commercial feasibility. Accordingly, a unique low-cost, ecofriendly, all-solution-processed, "bio-inspired" graphitic carbon (extracted from the most invasive plant species of Eichhornia crassipes: listed as one of the 100 most dangerous species by the International Union for Conservation of Nature) and a mixed halide perovskite interface-engineered, unique single-cell large-scale (10 × 10 sq.cm with an active area of 88 cm²) carbon-based perovskite solar cell (C-PSC) are demonstrated for the first time, delivering a maximum PCE of 6.32%. Notable performance was observed under low light performance for the interface-engineered champion device fabricated using the layer-to-layer approach, which, even when tested under fluorescent room light condition (at 200 lux of about ∼0.1 SUN illumination), exhibited a significant PCE. In terms of addressing the stability issues in the fabricated PSC devices, the present work has adopted a two-step strategy: the instability toward the extrinsic factors is addressed by encapsulation, and the subsequent intrinsic instability issue is also addressed through interfacial engineering. Surprisingly, when tested under various stability conditions (STC) such as ambient air, light (continuous 1 SUN, under room light illumination (0.1 SUN) and direct sunlight), severe damp up to a depth of ∼25 mm water (cold (∼15 °C) and hot (∼65 °C)), acidic pH (∼5), and alkaline pH (∼11)) conditions, the fabricated large-scale carbon-based perovskite solar cells (C-LSPSCs) retained unexpected long-term stability in their performance for over 50 days. As to appraise the performance superiority of the fabricated C-LSPSC devices under various aforesaid testing conditions, a working model of a mini-fan has been practically powered and demonstrated.

Net Zero Energy Districts: Connected Intelligence for Carbon-Neutral Cities

Net-Zero Energy Districts (NZEDs) are city districts in which the annual amount of CO2 emissions released is balanced by emissions removed from the atmosphere. NZEDs constitute a major component in a new generation of “smart-green cities”, which deploy both smart city technologies and renewable energy technologies. NZEDs promote environmental sustainability, contribute to cleaner environments and reduce global warming and the threats from climate change. This paper describes a model to assess the feasibility of the transition of city districts to self-sufficient NZEDs, based on locally produced renewable energy suitable for cities. It also aims to identify threshold conditions that allow for a city district to become a self-sufficient NZED using smart city systems, renewable energy, and nature-based solutions. The significance of transition to self-sufficient NZEDs is extremely important as it considerably decentralises and multiplies the efforts for carbon-neutral cities. The methodology we follow combines the literature review, model design, model feed with data, and many simulations to assess the outcome of the model in various climate, social, technology, and district settings. In the conclusion, we assess whether the transition to NZEDs with solar panel energy locally produced is feasible, we identify thresholds in terms of climate, population density, and solar conversion efficiency, and assess the compatibility of NZEDs with compact city planning principles.

Solution-processed two-dimensional materials for next-generation photovoltaics

In the ever-increasing energy demand scenario, the development of novel photovoltaic (PV) technologies is considered to be one of the key solutions to fulfil the energy request. In this context, graphene and related two-dimensional (2D) materials (GRMs), including nonlayered 2D materials and 2D perovskites, as well as their hybrid systems, are emerging as promising candidates to drive innovation in PV technologies. The mechanical, thermal, and optoelectronic properties of GRMs can be exploited in different active components of solar cells to design next-generation devices. These components include front (transparent) and back conductive electrodes, charge transporting layers, and interconnecting/recombination layers, as well as photoactive layers. The production and processing of GRMs in the liquid phase, coupled with the ability to "on-demand" tune their optoelectronic properties exploiting wet-chemical functionalization, enable their effective integration in advanced PV devices through scalable, reliable, and inexpensive printing/coating processes. Herein, we review the progresses in the use of solution-processed 2D materials in organic solar cells, dye-sensitized solar cells, perovskite solar cells, quantum dot solar cells, and organic-inorganic hybrid solar cells, as well as in tandem systems. We first provide a brief introduction on the properties of 2D materials and their production methods by solution-processing routes. Then, we discuss the functionality of 2D materials for electrodes, photoactive layer components/additives, charge transporting layers, and interconnecting layers through figures of merit, which allow the performance of solar cells to be determined and compared with the state-of-the-art values. We finally outline the roadmap for the further exploitation of solution-processed 2D materials to boost the performance of PV devices.

Laser fabricated carbon quantum dots in anti-solvent for highly efficient carbon-based perovskite solar cells

Additive passivation can be an effective strategy to regulate and control the properties of organic-inorganic halide perovskite film. In this article, carbon quantum dots (CQDs), fabricated by non-focused laser irradiation of carbon nanomaterial diluted in anti-solvent ethyl acetate, denoted as EACQDs, were adopted for perovskite film defect passivation and modification of carbon-based CH₃NH₃PbI₃ perovskite solar cells (PSCs). The size of EACQDs can be tuned by manipulating the laser fluence. The morphology of perovskite film was uncovered through scanning electron microscopy and atomic force microscopy. After embedding of EACQDs, the defect in perovskite crystal was reduced, resulting in the decreased carrier recombination and accelerated carrier transportation, which were demonstrated by electrochemical impedance spectroscopy, photoluminescence and time-resolved photoluminescence. As a consequence, with the optimization of 0.01 mg/mL EACQDs (1064 nm-300 mJ·pulse^-1·cm^-2-10 min), the power conversion efficiency (PCE) of carbon-based PSCs achieved a maximum value of 16.43%, which improved 23.81% when compared with the pristine PSCs of 13.27%. Furthermore, the EACQDs optimized PSCs also exhibited an excellent stability and still retained 86% of its initial PCE after 50-day storage at the room atmosphere with a humidity of 30-50%.

Efficient and Stable Carbon-Based Perovskite Solar Cells via Passivation by a Multifunctional Hydrophobic Molecule with Bidentate Anchors

Surface passivation has demonstrated to be an effective strategy to improve the power conversion efficiency (PCE) and long-term stability of perovskite solar cells (PSCs). Passivation treatment can effectively reduce the density of defect states at the surface and grain boundaries of perovskite films. Herein, a passivation agent of 2-amino-5-(trifluoromethyl)pyridine (5-TFMAP) with bidentate groups is applied to passivate perovskite CH₃NH₃PbI₃ films for the first time. Two types of electron-rich nitrogen atoms from both the pyridine ring and the amino group provide strong interaction with the under-coordinated Pb²⁺. Additionally, the trifluoromethyl group offers a hydrophobic property and improves moisture stability of the as-fabricated PSCs. It is found that the 5-TFMAP passivation layer can effectively reduce the defect states, promote better carrier transport, and suppress non-radiation recombination of the perovskite films. The best PCE of carbon-based PSCs passivated by the 5-TFMAP agent achieves a high efficiency of 14.96% compared with that of 11.90% for the control PSCs. Moreover, the long-term stability of PSCs with the 5-TFMAP passivation treatment is greatly improved, and its PCE can maintain 80% of its original PCE after being stored for 1200 h with a relative humidity of around 35% at room temperature.

Structure and Properties of (CH3NH3)3Tl2Cl9: A Thallium-Based Hybrid Perovskite-Like Compound

The new compound (CH₃NH₃)₃Tl₂Cl₉ was synthesized and fully characterized. X-ray photoelectron spectroscopy and Raman spectroscopy are consistent with the crystal structure solved by single-crystal X-ray diffraction. This compound is a semiconductor with a measured band gap of E_g = 2.91 eV. It is the first thallium-based hybrid perovskite and shows remarkably high stability to ambient conditions.

Transparent MoS2/PEDOT Composite Counter Electrodes for Bifacial Dye-Sensitized Solar Cells

Dye-sensitized solar cells (DSSCs) are solar energy conversion devices with high efficiency and simple fabrication procedures. Developing transparent counter electrode (CE) materials for bifacial DSSCs can address the needs of window-type building-integrated photovoltaics (BIPVs). Herein, transparent organic-inorganic hybrid composite films of molybdenum disulfide and poly(3,4-ethylenedioxythiophene) (MoS₂/PEDOT) are prepared to take full advantage of the conductivity and electrocatalytic ability of the two components. MoS₂ is synthesized by hydrothermal method and spin-coated to form the MoS₂ layer, and then PEDOT films are electrochemically polymerized on top of the MoS₂ film to form the composite CEs. The DSSC with the optimized MoS₂/PEDOT composite CE shows power conversion efficiency (PCE) of 7% under front illumination and 4.82% under back illumination. Compared with the DSSC made by the PEDOT CE and the Pt CE, the DSSC fabricated by the MoS₂/PEDOT composite CE improves the PCE by 10.6% and 6.4% for front illumination, respectively. It proves that the transparent MoS₂/PEDOT CE owes superior conductivity and catalytic properties, and it is an excellent candidate for bifacial DSSC in the application of BIPVs.

α-CsPbI3 Nanocrystals by Ultraviolet Light-Driven Oriented Attachment

Size and crystallinity of building units in the perovskite layer are of great significance to photovoltaic performance. Thus, to fabricate large-grain-size perovskite materials with the advantage of good crystallinity is quite necessary. The oriented attachment strategy has been proofed as an efficient method to control crystal growth. Herein, we reported on oriented attachment of α-CsPbI₃ quantum dots (QDs) into a large-grain-size nanocrystal under moderate ultraviolet (UV) light. By virtue of atomic-resolution TEM and X-ray absorption fine structure (XAFS) spectroscopy, we observed the UV-directed structure-evolution and growth process. This is trigged by UV-light illumination (7 W, 365 nm), which drives the oriented assembly of QDs into a large nanoparticle along {110} facets. Moreover, we also visualized a damage process of the α-CsPbI₃ QDs to photoinactive-δ-phase ones and finally into PbI₂ under high-power UV-light (100 W, 365 nm) exposure. The findings provide a prototype for fabricating large-size perovskite nanostructures with promising properties.

Molecularly engineered hole-transport material for low-cost perovskite solar cells

Triphenylamine-N-phenyl-4-(phenyldiazenyl)aniline (TPA-AZO) is synthesized via a facile CuI-catalyzed reaction and used as a hole transport material (HTM) in perovskite solar cells (PSCs), as an alternative to the expensive spiro-type molecular materials, including commercial 2,2',7,7'-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9'-spirobifluorene (spiro-OMeTAD). Experimental and computational investigations reveal that the highest occupied molecular orbital (HOMO) level of TPA-AZO is deeper than that of spiro-OMeTAD, and optimally matches with the conduction band of the perovskite light absorber. The use of TPA-AZO as a HTM results in PSC prototypes with a power conversion efficiency (PCE) approaching that of the spiro-OMeTAD-based reference device (17.86% vs. 19.07%). Moreover, the use of inexpensive starting reagents for the synthesis of TPA-AZO makes the latter a new affordable HTM for PSCs. In particular, the cost of 1 g of TPA-AZO ($22.76) is significantly lower compared to that of spiro-OMeTAD ($170-475). Overall, TPA-AZO-based HTMs are promising candidates for the implementation of viable PSCs in large-scale production.

Interfacial electronic features in methyl-ammonium lead iodide and p-type oxide heterostructures: new insights for inverted perovskite solar cells

First-principles simulations unveil the interface electronic structures of MAPI/NiO and MAPI/CuGaO₂ heterojunctions in inverted perovskite solar cells.

Hydrophobic polythiophene hole-transport layers to address the moisture-induced decomposition problem of perovskite solar cells

Perovskite solar cells have emerged as one of the most promising next-generation photovoltaic technologies and have achieved a record power conversion efficiency of 22.7%. The technology meets industrial demands for cost effectiveness and scalability; however, the instability of lead halide perovskites toward moisture is a major barrier to their commercial development. Previous studies have revealed that the use of hydrophobic hole-transport layers (e.g., poly(3-hexylthiophene), P3HT) can slow the ingress of water vapor and improve the lifetime of the underlying perovskite, suggesting a route to longer lived devices. In this work, we report the synthesis of a variety of poly(3-alkoxythiophenes) with different side chains. The side chains range from hydrophilic (triethylene glycol methyl ether) to extremely hydrophobic (highly fluorinated hexyloxy). We evaluated the polymers, alongside commercially available P3HT, for their ability to stabilize methylammonium lead iodide films at high relative humidities. The fluorinated polythiophenes were able to substantially improve the perovskite lifetime, suggesting that more hydrophobic hole-transport layers may be a route to more stable perovskite solar cells.

Perovskite Photovoltaics: The Significant Role of Ligands in Film Formation, Passivation, and Stability

Due to their outstanding optoelectronic properties, metal halide perovskites have been intensively studied in recent years. The latest certificated efficiency of 23.3% recently achieved in perovskite solar cells (PVSCs) enables them to be used as a very promising candidate for next-generation photovoltaics. The morphology, defect density, and water resistance of perovskite films have an enormous impact on the performance and stability of PVSCs. Ligands, with coordinating capability, have been widely developed to improve the quality and stability of perovskite materials significantly. In the first section of this review, the role of ligands in fabricating perovskite films by different methods (one-step, two-step, and postdeposition treatment) is discussed. In the second section, the progress on ligand-passivated perovskites via post-treatment, in situ passivation during perovskite formation, and modifying the substrates before perovskite formation is reviewed. In the third section, a discussion of ligand-stabilized perovskite films from the perspectives of crystal crosslinking, dimensionality engineering, and interfacial modification is presented. Finally, a summary and an outlook are given.

Anion exchange in inorganic perovskite nanocrystal polymer composites

We demonstrate a facile, low-cost and room-temperature method of anion exchange in cesium lead bromide nanocrystals (CsPbBr3 NCs), embedded into a polymer matrix. The anion exchange occurs upon exposure of the solid CsPbBr3 NCs/PDMS nanocomposite to a controlled anion precursor gas atmosphere. The rate and extent of the anion exchange reaction can be controlled via the variation of either the exposure time or the relative concentration of the anion precursor gas. Post-synthesis chemical transformation of perovskite nanocrystal-polymer composites is not readily achievable using conventional methods of anion exchange, which renders the gas-assisted strategy extremely useful. We envisage that this work will enable the development of solid-state perovskite NC optoelectronic devices.

Dye-sensitized photoelectrochemical water oxidation through a buried junction

Water oxidation has long been a challenge in artificial photosynthetic devices that convert solar energy into fuels. Water-splitting dye-sensitized photoelectrochemical cells (WS-DSPECs) provide a modular approach for integrating light-harvesting molecules with water-oxidation catalysts on metal-oxide electrodes. Despite recent progress in improving the efficiency of these devices by introducing good molecular water-oxidation catalysts, WS-DSPECs have poor stability, owing to the oxidation of molecular components at very positive electrode potentials. Here we demonstrate that a solid-state dye-sensitized solar cell (ss-DSSC) can be used as a buried junction for stable photoelectrochemical water splitting. A thin protecting layer of TiO₂ grown by atomic layer deposition (ALD) stabilizes the operation of the photoanode in aqueous solution, although as a solar cell there is a performance loss due to increased series resistance after the coating. With an electrodeposited iridium oxide layer, a photocurrent density of 1.43 mA cm^-2 was observed in 0.1 M pH 6.7 phosphate solution at 1.23 V versus reversible hydrogen electrode, with good stability over 1 h. We measured an incident photon-to-current efficiency of 22% at 540 nm and a Faradaic efficiency of 43% for oxygen evolution. While the potential profile of the catalyst layer suggested otherwise, we confirmed the formation of a buried junction in the as-prepared photoelectrode. The buried junction design of ss-DSSs adds to our understanding of semiconductor-electrocatalyst junction behaviors in the presence of a poor semiconducting material.

Efficient Bifacial Semitransparent Perovskite Solar Cells Using Ag/V2O5 as Transparent Anodes

Bifacial semitransparent inverted planar structured perovskite solar cells (PSCs) based on Cs_0.05FA_0.3MA_0.7PbI_2.51Br_0.54 using an Ag thin film electrode and V₂O₅ optical coupling layer are investigated theoretically and experimentally. It is shown that the introduction of the cesium (Cs) ions in the perovskite could obviously improve the device performance and stability. When only the bare Ag film electrode is used, the PSCs show a bifacial performance with the power conversion efficiency (PCE) of 14.62% illuminated from the indium tin oxide (ITO) side and 5.45% from the Ag film side. By introducing a V₂O₅ optical coupling layer, the PCE is enhanced to 8.91% illuminated from the Ag film side, which is 63% improvement compared with the bare Ag film electrode, whereas the PCE illuminated from the ITO side remains almost unchanged. Moreover, when a back-reflector is employed, the PCE of device could be further improved to 15.39% by illumination from the ITO side and 12.44% by illumination from the Ag side. The devices also show superior semitransparent properties and exhibit negligible photocurrent hysteresis, irrespective of the side from which the light is illuminated. In short, the Ag/V₂O₅ double layer is a promising semitransparent electrode due to its low cost and simple preparation process, which also point to a new direction for the bifacial PSCs and tandem solar cells.

High-performance gas sensors based on a thiocyanate ion-doped organometal halide perovskite

Thin films of a thiocyanate ion (SCN^-)-doped organometal halide perovskite, CH₃NH₃PbI_3-x(SCN)_x, were used as a sensing material for developing high-performance gas sensors. The CH₃NH₃PbI_3-x(SCN)_x-based chemiresistor-type sensor can sensitively and selectively detect acetone and nitrogen dioxide (NO₂) at room temperature with high sensitivities of 5.6 × 10^-3 and 5.3 × 10^-1 ppm^-1. The limits of detection for acetone and NO₂ were measured to be 20 ppm and 200 ppb. This sensor also exhibited excellent repeatability, and its environmental stability was greatly improved by doping the perovskite with SCN^- ions.

Realizing Efficient Lead-Free Formamidinium Tin Triiodide Perovskite Solar Cells via a Sequential Deposition Route

Recently, the evolved intermediate phase based on iodoplumbate anions that mediates perovskite crystallization has been embodied as the Lewis acid-base adduct formed by metal halides (serve as Lewis acid) and polar aprotic solvents (serve as Lewis base). Based on this principle, it is proposed to constitute efficient Lewis acid-base adduct in the SnI₂ deposition step to modulate its volume expansion and fast reaction with methylammonium iodide (MAI)/formamidinium iodide (FAI) (FAI is studied hereafter). Herein, trimethylamine (TMA) is employed as the additional Lewis base in the tin halide solution to form SnY₂ -TMA complexes (Y = I^- , F^- ) in the first-step deposition, followed by intercalating with FAI to convert into FASnI. It is shown that TMA can facilitate homogeneous film formation of a SnI₂ (+SnF₂ ) layer by effectively forming intermediate SnY₂ -TMA complexes. Meanwhile, its relatively larger size and weaker affinity with SnI₂ than FA+ ions will facilitate the intramolecular exchange with FA+ ions, thereby enabling the formation of dense and compact FASnI₃ film with large crystalline domain (>1 µm). As a result, high power conversion efficiencies of 4.34% and 7.09% with decent stability are successfully accomplished in both conventional and inverted perovskite solar cells, respectively.

Frequency and temperature-dependence of dielectric permittivity and electric modulus studies of the solid solution Ca0.85Er0.1Ti1−xCo4x/3O3 (0 ≤ x ≤ 0.1)

The dielectric properties of Ca_0.85Er_0.1Ti_1−xCo_4x/3O₃ (CETCo_x) (x = 0.00, 0.05 and 0.10), prepared by a sol–gel method, were systematically characterized. The temperature and frequency dependence of the dielectric properties showed a major effect of the grain and grain boundary. The dielectric constant and dielectric loss of CETCo_x decreased sharply with increasing frequency. This is referred to as the Maxwell–Wagner type of polarization in accordance with Koop's theory. As a function of temperature, the dielectric loss and the real part of permittivity decreased with increasing frequency as well as Co rate. Indeed, a classical ferroelectric behavior was observed for x = 0.00. The non-ferroelectric state of the grain boundary and its correlation with structure, however, proved the existence of a relaxor behavior for x = 0.05 and 0.10. The complex electric modulus analysis M*(ω) confirmed that the relaxation process is thermally activated. The normalized imaginary part of the modulus indicated that the relaxation process is dominated by the short range movement of charge carriers.

Frequency dependence of real (ε′) part of permittivity of CETCo_x for x = 0.00, 0.05 and 0.10 for T = 600 K.

First-principles study of anion diffusion in lead-free halide double perovskites

In this work, halide ion diffusion in lead-free halide double perovskites Cs₂AgBiX₆ (X = Cl, Br), Cs₂AgSbCl₆ and Cs₂AgInCl₆ was investigated by first-principles calculations.

Constructing Efficient and Stable Perovskite Solar Cells via Interconnecting Perovskite Grains

A high-quality perovskite film with interconnected perovskite grains was obtained by incorporating terephthalic acid (TPA) additive into the perovskite precursor solution. The presence of TPA changed the crystallization kinetics of the perovskite film and promoted lateral growth of grains in the vicinity of crystal boundaries. As a result, sheet-shaped perovskite was formed and covered onto the bottom grains, which made some adjacent grains partly merge together to form grains-interconnected perovskite film. Perovskite solar cells (PSCs) with TPA additive exhibited a power conversion efficiency (PCE) of 18.51% with less hysteresis, which is obviously higher than that of pristine cells (15.53%). PSCs without and with TPA additive retain 18 and 51% of the initial PCE value, respectively, aging for 35 days exposed to relative humidity 30% in air without encapsulation. Furthermore, MAPbI₃ film with TPA additive shows superior thermal stability to the pristine one under 100 °C baking. The results indicate that the presence of TPA in perovskite film can greatly improve the performance of PSCs as well as their moisture resistance and thermal stability.

Progress on Perovskite Materials and Solar Cells with Mixed Cations and Halide Anions

Organic-inorganic halide perovskite materials (e.g., MAPbI₃, FAPbI₃, etc.; where MA = CH₃NH₃⁺, FA = CH(NH₂)₂⁺) have been studied intensively for photovoltaic applications. Major concerns for the commercialization of perovskite photovoltaic technology to take off include lead toxicity, long-term stability, hysteresis, and optimal bandgap. Therefore, there is still need for further exploration of alternative candidates. Elemental composition engineering of MAPbI₃ and FAPbI₃ has been proposed to address the above concerns. Among the best six certified power conversion efficiencies reported by National Renewable Energy Laboratory on perovskite-based solar cells, five are based on mixed perovskites (e.g., MAPbI_1-xBr_x, FA_0.85MA_0.15PbI_2.55Br_0.45, Cs_0.1FA_0.75MA_0.15PbI_2.49Br_0.51). In this paper, we review the recent progress on the synthesis and fundamental aspects of mixed cation and halide perovskites correlating with device performance, long-term stability, and hysteresis. In the outlook, we outline the future research directions based on the reported results as well as related topics that warrant further investigation.

Light and Electrically Induced Phase Segregation and Its Impact on the Stability of Quadruple Cation High Bandgap Perovskite Solar Cells

Perovskite material with a bandgap of 1.7-1.8 eV is highly desirable for the top cell in a tandem configuration with a lower bandgap bottom cell, such as a silicon cell. This can be achieved by alloying iodide and bromide anions, but light-induced phase-segregation phenomena are often observed in perovskite films of this kind, with implications for solar cell efficiency. Here, we investigate light-induced phase segregation inside quadruple-cation perovskite material in a complete cell structure and find that the magnitude of this phenomenon is dependent on the operating condition of the solar cell. Under short-circuit and even maximum power point conditions, phase segregation is found to be negligible compared to the magnitude of segregation under open-circuit conditions. In accordance with the finding, perovskite cells based on quadruple-cation perovskite with 1.73 eV bandgap retain 94% of the original efficiency after 12 h operation at the maximum power point, while the cell only retains 82% of the original efficiency after 12 h operation at the open-circuit condition. This result highlights the need to have standard methods including light/dark and bias condition for testing the stability of perovskite solar cells. Additionally, phase segregation is observed when the cell was forward biased at 1.2 V in the dark, which indicates that photoexcitation is not required to induce phase segregation.

NiO x Hole Transport Layer for Perovskite Solar Cells with Improved Stability and Reproducibility

In this study, highly stable, low-temperature-processed planar lead halide perovskite (MAPbI_3-x Cl _x ) solar cells with NiO _x interfaces have been developed. Our solar cells maintain over 85% of the initial efficiency for more than 670 h, at the maximum power point tracking (MPPT) under 1 sun illumination (no UV-light filtering) at 30 °C, and over 73% of the initial efficiency for more than 1000 h, at the accelerating aging test (85 °C) under the same MPPT condition. Storing the encapsulated devices at 85 °C in dark over 1000 h revealed no performance degradation. The key factor for the prolonged lifetime of the devices was the sputter-deposited polycrystalline NiO _x hole transport layer (HTL). We observed that the properties of NiO _x are dependent on its composition. At a higher Ni³⁺/Ni²⁺ ratio, the conductivity of NiO _x is higher, but at the expense of optical transmittance. We obtained the highest power conversion efficiency of 15.2% at the optimized NiO _x condition. The sputtered NiO _x films were used to fabricate solar cells without annealing or any other treatments. The device stability enhanced significantly compared to that of the devices with PEDOT:PSS HTL. We clearly demonstrated that the illumination-induced degradation depends heavily on the nature of the HTL in the inverted perovskite solar cells (PVSCs). The sputtered NiO _x HTL can be a good candidate to solve stability problems in the lead halide PVSCs.

The interface degradation of planar organic–inorganic perovskite solar cell traced by light beam induced current (LBIC)

The light beam induced current (LBIC) method was adopted to nondestructively map the photoresponse of real planar organic–inorganic hybrid perovskite solar cells (PSCs).