Inorganic Films Research Articles

Intermediate Phase Modification Enables High‐Performance Iodine‐Rich Inorganic Perovskite Solar Cells with 3000‐Hour Stability

AbstractThe presence of excess secondary‐phase PbI2 in perovskite films shows a negative impact on their long‐term stability. Herein, an intermediate phase modification (IPM) strategy is proposed to eliminate residual PbI2 for improved quality of all‐inorganic CsPbI3‐type perovskite films, wherein the extrinsic agent is introduced to address the intermediate phase. By transforming residual PbI2 into a novel 1D perovskite phase, the IPM strategy acts as a patch to suture grain boundaries in the inorganic perovskite films. In addition, the IPM strategy not only enhances the quality of perovskite films but also mitigates energy disorder, reduces trap state density, and prolongs carrier lifetime by expediting the intermediate phase conversion process and passivating surface defects. As such, the perovskite solar cells (PSCs) with a high power conversion efficiency (PCE) of ≈20% and a high fill factor of 83.3% are considered to be very efficient, with excellent shelf stability of 3000 h of exposure in air without any encapsulation. This work not only exhibits a novel optimization route for inorganic perovskite but also emphasizes the crucial role of eliminating residual PbI2 in inorganic perovskites.

Lyotropic Liquid Crystals of Colloidal Gibbsite Nanoplatelets: Phase Transition, Kinetic Characterization, and Confinement Effect

Abstract2D gibbsite nanoplatelets, [γ‐Al(OH)3], are widely used as an inorganic mineral platform for 2D lyotropic liquid crystal (LC) colloids. These particles are synthesized and enlarged using an improved hydrolysis method, resulting in highly crystalline (96.5%), low polydispersity (15.1%), and readily dispersible colloids in water. The aqueous mesomorphic system is characterized for the isotropic‐to‐nematic phase transition by analyzing number density and shear viscosity. Thermal stability is assessed through thermogravimetric analysis. Additionally, kinetic and thermodynamic parameters for 2D gibbsite nanoparticles are determined for the first time using three models (Coats‐Redfern, Friedman, and Kissinger). In particular, the activation and Gibbs free energies for the first dehydration stage of gibbsite yield ranges of 98‒128 kJ mol−1 and 135‒161 kJ mol−1, respectively. To investigate the confinement effect of colloidal gibbsite‐LCs, an isotropic gibbsite dispersion is introduced into a tube, leading to the uniform formation of gibbsite‐LC layers along two distinct pathways: tangential to the liquid‐air interface and as concentric circles along the tube walls. These findings offer valuable insights into potential applications, particularly in the domain of gas barrier inorganic films across various specialized fields.

Cytidylic acid improves crystal growth, defect passivation and flexibility of inorganic CsPbI2Br film for inverted photovoltaics towards versatile applications

Cesium-based all-inorganic perovskites have been of great interest due to their excellent thermal and light stability. However, these inorganic perovskites more often suffer from poor crystallization and unfavorable mechanical flexibility, hence delivering inferior photovoltaic performance and limited device lifetime. In this work, cytidine 5ʹ-monophosphate (5ʹ-CMP), a natural organics with multiple functional groups, is used as an additive to facilitate the crystallization of CsPbI2Br film, and meanwhile to mitigate the interfacial defects and residual strain, which could be attributed to the strong interactions between 5ʹ-CMP and PbI2 precursor as well as perovskite lattice. As a result, the optimal devices with an inverted structure exhibit an enhanced efficiency of 15.94% or 33.22% along with excellent operational stability under one-sun or white light emitting diode (WLED) illumination conditions. In addition, the perovskite film with 5ʹ-CMP exhibits a reduced modulus, hence rendering the flexible devices with improved mechanical stability. This work thus demonstrates a promising strategy to optimize inverted all-inorganic perovskite devices for versatile applications.

Acetate-based ionic liquid engineering for efficient and stable CsPbI2Br perovskite solar cells with an unprecedented fill factor over 83%

The current investigation addresses the persistent challenge of poor ambient stability exhibited by inorganic lead halide perovskites, primarily stemming from intrinsic phase transitions and the presence of defect states. This area of research has been considerably unexplored thus far. On the other hand, the notable effects of ionic liquids (ILs) in improving both stability and efficiency of perovskite photovoltaics have been substantial. In line with these developments, this study endeavors to synergize these two critical domains by introducing an acetate (Ac)-based IL into the inorganic perovskite precursor solution to tailor the crystal growth and charge carrier dynamics in CsPbI2Br films, resulting in prolonged stability and enhanced photovoltaic performance. The integration of 1-butyl-3-methylimidazolium acetate (BMIMAc) can indeed accelerate the crystallization of the inorganic perovskite film by interacting the Ac− anion with uncoordinated Pb2+ cation in CsPbI2Br. This interaction prompts the formation of smaller grains, which in turn inhibits the creation of non-photoactive phases. Moreover, the presence of BMIMAc as a passivation agent introduces significant defect-healing capabilities, eliminated charge recombination, and increased hydrophobicity. This work endeavors to pave the way for high-efficiency, enduring, and more robust inorganic PSCs through the integration of innovative materials and advanced understanding of fundamental principles, resulting uniform and dense perovskite film. Accordingly, 1.1 mol% BMIMAc-passivated device enables an impressive efficiency of 15.6% with an unprecedented fill factor (FF) exceeding 83%. Remarkably, even after undergoing extended light-soaking for 600 h, the BMIMAc-passivated device retains approximately 85% of its initial efficiency.

Solvent Annealing Enabling Reconstruction of Cadmium Sulfide Film for Improved Heterojunction Quality and Photovoltaic Performance of Antimony Selenosulfide Solar Cells

AbstractAntimony selenosulfide, Sb2(S,Se)3, has been considered as new‐generation light‐harvesting material for high‐efficiency photovoltaic applications due to its adjustable bandgap, high absorption coefficient, and excellent stability. In terms of device operation, the electron transfer from the electron transporting layer to Sb2(S,Se)3 layer plays a critical role in improving the photovoltaic energy conversion efficiency of solar devices. Intricately manipulating the surface and interface properties has been a great challenge in solar cell fabrications. Herein, an effective approach toward the reconstruction of the CdS interfacial layer, and the following Sb2(S,Se)3 absorber film by utilizing polar ethylenediamine (EDA) solvent annealing at room temperature is developed. It is found that the presence of nitrogen‐containing functional groups of EDA on the CdS surface not only promotes the grain growth and crystallization of CdS, but also induces optimized deposition of Sb2(S,Se)3 films in terms of interfacial contact and defect formation. Finally, the Sb2(S,Se)3 solar cell based on EDA–CdS achieves a top efficiency of 10.10%. This study provides an efficient method and a new understanding of chemically healing inorganic thin films.

Flexible multifunctional titania nanotube array platform for biological interfacing

The current work presents a novel flexible multifunctional platform for biological interface applications. The use of titania nanotube arrays (TNAs) as a multifunctional material is explored for soft-tissue interface applications. In vitro biocompatibility of TNAs to brain-derived cells was first examined by culturing microglia cells—the resident immune cells of the central nervous system on the surface of TNAs. The release profile of an anti-inflammatory drug, dexamethasone from TNAs-on-polyimide substrates, was then evaluated under different bending modes. Flexible TNAs-on-polyimide sustained a linear release of anti-inflammatory dexamethasone up to ~11 days under different bending conditions. Finally, microfabrication processes for patterning and transferring TNA microsegments were developed to facilitate structural stability during device flexing and to expand the set of compatible polymer substrates. The techniques developed in this study can be applied to integrate TNAs or other similar nanoporous inorganic films onto various polymer substrates.Impact statementTitania nanotube arrays (TNAs) are highly tunable and biocompatible structures that lend themselves to multifunctional implementation in implanted devices. A particularly important aspect of titania nanotubes is their ability to serve as nano-reservoirs for drugs or other therapeutic agents that slowly release after implantation. To date, TNAs have been used to promote integration with rigid, dense tissues for dental and orthopedic applications. This work aims to expand the implant applications that can benefit from TNAs by integrating them onto soft polymer substrates, thereby promoting compatibility with soft tissues. The successful direct growth and integration of TNAs on polymer substrates mark a critical step toward developing mechanically compliant implantable systems with drug delivery from nanostructured inorganic functional materials. Diffusion-driven release kinetics and the high drug-loading efficiency of TNAs offer tremendous potential for sustained drug delivery for scientific investigations, to treat injury and disease, and to promote device integration with biological tissues. This work opens new opportunities for developing novel and more effective implanted devices that can significantly improve patient outcomes and quality of life.Graphical abstract

Scalable Photochromic Film for Solar Heat and Daylight Management.

The adaptive control of sunlight through photochromic smart windows could have a huge impact on the energy efficiency and daylight comfort in buildings. However, the fabrication of inorganic nanoparticle and polymer composite photochromic films with a high contrast ratio and high transparency/low haze remains a challenge. Here, a solution method is presented for the in situ growth of copper-doped tungsten trioxide nanoparticles in polymethyl methacrylate, which allows a low-cost preparation of photochromic films with a high luminoustransparency (luminous transmittance Tlum = 91%) and scalability (30 × 350 cm2 ). High modulation of visible light (ΔTlum = 73%) and solar heat (modulation of solar transmittance ΔTsol = 73%, modulation of solar heat gain coefficient ΔSHGC = 0.5) of the film improves the indoor daylight comfort and energy efficiency. Simulation results show that low-e windows with the photochromic film applied can greatly enhance the energy efficiency and daylight comfort. This photochromic film presents an attractive strategy for achieving more energy-efficient buildings and carbon neutrality to combat global climate change.

High electrical characteristics through graphene oxide doping process on physicochemically reformed inorganic thin films.

This study investigated the improvement of the electro-optical properties of a liquid crystal (LC) cell fabricated through brush coating using graphene oxide (GO) doping. The physical deformation of the surface was analyzed using atomic force microscopy. The size of the groove increased as the GO dopant concentration increased, but the direction of the groove along the brush direction was maintained. X-ray photoelectron spectroscopy analysis confirmed that the number of C-C and O-Sn bonds increased as the GO concentration increased. Since the van der Waals force on the surface increases as the number of O-metal bonds increases, we were able to determine why the anchoring energy of the LC alignment layer increased. This was confirmed by residual DC voltage and anchoring energy measurements that were later performed. As the GO concentration increased, the width of the hysteresis curve decreased, indicating that the residual DC voltage decreased. Additionally, the 15% GO-doped sample exhibited a significant increase in its anchoring energy up to 1.34 × 10-3J/m2, which is similar to that of rubbed polyimide. It also secured a high level of electro-optical properties and demonstrated potential as a next-generation thin-film display despite being produced via a simple brush-coating process.

Nanoscale Vertical Resolution in Optical Printing of Inorganic Nanoparticles.

Direct optical printing of functional inorganics shows tremendous potential as it enables the creation of intricate two-dimensional (2D) patterns and affordable design and production of various devices. Although there have been recent advancements in printing processes using short-wavelength light or pulsed lasers, the precise control of the vertical thickness in printed 3D structures has received little attention. This control is vital to the diverse functionalities of inorganic thin films and their devices, as they rely heavily on their thicknesses. This lack of research is attributed to the technical intricacy and complexity involved in the lithographic processes. Herein, we present a generalized optical 3D printing process for inorganic nanoparticles using maskless digital light processing. We develop a range of photocurable inorganic nanoparticle inks encompassing metals, semiconductors, and oxides, combined with photolinkable ligands and photoacid generators, enabling the direct solidification of nanoparticles in the ink medium. Our process creates complex and large-area patterns with a vertical resolution of ∼50 nm, producing 50-nm-thick 2D films and several micrometer-thick 3D architectures with no layer height difference via layer-by-layer deposition. Through fabrication and operation of multilayered switching devices with Au electrodes and Ag-organic resistive layers, the feasibility of our process for cost-effective manufacturing of multilayered devices is demonstrated.

Defect Passivation and Lithium Ion Coordination Via Hole Transporting Layer Modification for High Performance Inorganic Perovskite Solar Cells.

Metal halide inorganic perovskite solar cells (PSCs) have great potential to achieve high efficiency with excellent thermal stability. However, the surface defect traps restrain the achievement of high open circuit voltage (VOC ) and power conversion efficiency (PCE) of the devices due to the severe nonradiative charge recombination. Moreover, the state-of-the-art hole transporting layer (HTL) significantly hampers device moisture stability, even though it renders the highest solar cell efficiency. Herein, a one-stone-two-birds strategy is proposed using a biocompatible material tryptamine (TA) as an additive in HTL. First, TA bearing electron rich moieties can favorably passivate the surface defects of inorganic perovskite films, significantly reducing trap density and prolonging charge lifetime. It results in a drastic improvement of VOC from 1.192 to 1.251V, with a VOC loss of 0.48V. The corresponding PSCs achieve a 21.8% PCE under 100mW cm-2 illumination. Second, TA in HTL can coordinate with lithium cations, retarding their reaction with moisture and increasing the moisture stability of HTL. Consequently, the black phase of inorganic perovskite films is well preserved, and the corresponding PSCs maintain 90% of the initial PCE after 800h storage at relative humidity of 25-35%, much higher than the control devices.

Efficient two-step sequential deposition perovskite solar cells via PbCl2 enhanced PbI2 precursor

Two-step sequentially deposited FAPbI3 polycrystalline film is adopted to produce high-performance perovskite solar cells (PSCs) with outstanding power conversion efficiency (PCE). The pore-forming of the inorganic film is beneficial to the second organic salt infiltrate, thus promoting a solid-solution reaction. Here, lead chloride (PbCl2) is introduced into lead iodide (PbI2) precursor solution to adjust the properties of PbI2 membranes and obtain a micrometer-sized perovskite layer by reducing grain boundary defects. The incorporation of PbCl2 reduces bulk defects and improves the device's performance. The PSCs displayed good operational stability in the dry atmosphere over 2 months. The PCE of PSCs exhibited an increased trend in the initial measurement and then showed decreased trend. A champion PCE of 22.07% was obtained after storage. Furthermore, the PL/TRPL of perovskite film and perovskite/Spiro-OMeTAD interface was tested to explain the efficiency evolution. This work may provide a strategy for further improving the performance of PSCs via fine-controlled PbI2 membranes in the perovskite layer.

Guided Search to Self‐Healing in Semiconductors

AbstractSelf‐healing (SH) of (opto)electronic material damage can have a huge impact on resource sustainability. The rising interest in halide perovskite (HaP) compounds over the past decade is due to their excellent semiconducting properties for crystals and films, even if made by low‐temperature solution‐based processing. Direct proof of self‐healing in Pb‐based HaPs is demonstrated through photoluminescence recovery from photodamage, fracture healing and their use as high‐energy radiation and particle detectors. Here, the question of how to find additional semiconducting materials exhibiting SH, in particular lead‐free ones is addressed. Applying a data‐mining approach to identify semiconductors with favorable mechanical and thermal properties, for which Pb HaPs are clear outliers, it is found that the Cs2AuIAuIIIX6, (X = I, Br, Cl) family, which is synthesized and tested for SH. This is the first demonstration of self‐healing of Pb‐free inorganic HaP thin films, by photoluminescence recovery.

Critical role of post-treatment induced surface reconstruction for high performance inorganic tin-lead perovskite solar cells

Inorganic CsPb0.7Sn0.3I3 perovskites with low-bandgap (1.2 to 1.4 eV) are desired absorber materials for solar cells owing to their ideal bandgap and compositional stability. However, the performances of inorganic Pb-Sn perovskite solar cells are much lower than their Pb-based and hybrid Pb-Sn (e.g. CsPbX3 and FAMAPbSnX3) PSCs, which might be ascribed to its poor film-forming morphology and easy oxidation of Sn2+ at the surface. Here, for the first time, a combined 1-(4-fluorophenyl) piperazine (1-4FP) additive and 1-4FP post-treatment strategy was adopted to obtain high-quality pinhole-free films through a significant surface reconstruction. Specifically, the interaction introduced by 1-4FP post-treatment can effectively prevent the inevitable Sn2+ oxidation on perovskite surface, resulting from crosslinking neighboring perovskite grains with hydrogen bonds of amine group binding to the perovskite surface. As a result, the device treated by this combined strategy achieved a PCE of 17.19 %, which is the highest efficiency of Pb-Sn alloyed inorganic PSCs (sub-1.4 eV) reported to date. In addition, the unsealed 1-4FP-treated devices maintained their initial efficiencies of approximately 100 % after storage in a nitrogen atmosphere for 4000 h. Our findings open a new avenue to obtain high-quality inorganic Pb-Sn perovskite films and associated solar cells.

Polymeric Hole‐Selective Contact for Crystalline Silicon Solar Cells

Carrier‐selective contacts based on inorganic materials (e.g., silicon layers and metal oxides) have been intensively investigated for efficient crystalline silicon (c‐Si) photovoltaics. Compared to the vacuum deposition process for inorganic films, organic semiconductors offer a simplified and low‐cost processing. Herein, solution‐processed poly[bis(4‐phenyl) (2,4,6‐trimethylphenyl) amine] (PTAA) is developed as hole‐selective contact for c‐Si solar cells. PTAA exhibits a suitable band alignment with p‐type c‐Si, featuring a small valence band offset (≈0.1 eV) and a large conduction band offset (≈2.2 eV) for effective electron blocking. PTAA combined with Al2O3 passivation interlayer is demonstrated to simultaneously offer a low contact resistivity (36.5 mΩ cm2) and a moderate surface passivation (implied open‐circuit voltage 635.6 mV) on p‐type c‐Si surface. By the implementation of a full‐area hole‐selective Al2O3/PTAA rear contact, a champion efficiency of 20.2% is achieved on the hybrid c‐Si solar cells. Herein, a guiding principle for future research on polymeric carrier‐selective contact for c‐Si solar cells is provided.

The Impact of Ligand Removal on the Optoelectronic Properties of Inorganic and Hybrid Lead Halide Perovskite Nanocrystal Films

AbstractLigand exchange performed during or after the colloidal synthesis of nanocrystals (NCs) provides an efficient way to produce conductive NC solids for optoelectronics. Herein, a post‐synthetic ligand washing process is developed and applied to two different combinations of ligands and perovskite NCs, namely robust green CsPbBr3 NCs capped by didodecyldimethylammonium bromide and near‐infrared FAPbI3 NCs decorated by weakly bound oleic acid ligands. The impact of such processes on the morphological and optoelectronic NC properties is examined while exploring parameters such as the reaction time and the influence of oxygen and humidity. For the FAPbI3 NCs, ligand washing results in extended NC aggregation and substantial photoluminescence loss, with the treatment becoming more aggressive for air‐exposed films. For the CsPbBr3 NCs, the process is insensitive to the environmental conditions and results in partial ligand shell loss and NC close packing rather than bulk‐like aggregation while affecting less the optical properties. Upon ligand removal, the photoconductance increases by up to ≈90% and ≈60% for FAPbI3 NCs and CsPbBr3 NCs, respectively. THz spectroscopy produces qualitatively similar trends of the conductivity with ligand removal time, with THz mobility values as high as 30 and 6 V−1s−1cm2 for glove box prepared FAPbI3 and CsPbBr3 NCs, respectively.

High-performance amplified spontaneous emission in inorganic CsPbBr3 perovskite thin films grown on engineered quartz substrates.

In this work, periodic rectangular arrays were fabricated on quartz substrates using the femtosecond laser ablation technique, on which inorganic cesium lead bromide thin films were grown using the spin coating method. Enhanced photoluminescence emission was investigated using a homebuilt confocal microscope, and increased light absorption due to the engineered structures was also measured. High-performance amplified spontaneous emission with typical narrow lasing emission peaks excited using a nanosecond laser centered at 266 nm was obtained. This work provides a method to modify the performance of optoelectrical devices, which helps develop light-emitting diodes, photodetectors, solar cells, and lasers.

The temporal response of inorganic temperature-sensitive phosphor films with different layer thickness and composition

The temporal response of inorganic temperature-sensitive phosphor films with different layer thickness and composition

Excellent triboelectric properties of P(VDF-TrFE) nanofibers incorporated with Bi-based oxide-modified KNN polycrystals

Recently, improving triboelectric nanogenerator (TENG) performance with inorganic nanofillers and crafting multifunctional nanofiber films via electrospinning have gained much attention. This paper explores the effect of electrospun composite nanofibers based on P(VDF-TrFE) (denoted as PT) with K0.5Na0.5NbO3 (KNN) polycrystals doped with bismuth-based (Bi-based) oxides [Bi(Ni0.5Hf0.5)O3 (BNH) and Bi(Mg0.5Zr0.5)O3 (BMZ)] on the output performance of TENG. TENGs with four types of [PT-PET, (PT/KNN)-PET, (PT/KNN-BNH)-PET, and (PT/KNN-BMZ)-PET] are compared, and the output increases progressively from pristine (Voc = 572 V and Isc = 13.4 μA) to PT/KNN-BMZ (Voc = 831 V and Isc = 39.2 μA). The maximum output performance is higher than that of most previously reported inorganic particle-modified films. Electrospinning provides a high applied voltage, enhancing dipole alignment, which aids in the formation of the β-phase. Additionally, modifying KNN ceramics with BNH and BMZ and using them as nano-fillers not only increases the β-phase of P(VDF-TrFE) but also elevates its dielectric constant, enhancing the capacitance of TENG, thereby yielding superior triboelectric performance. Furthermore, when different KNN/BMZ concentrations are compared, the (PT/4% KNN-BMZ)-PET TENG demonstrates the optimum triboelectric output performance, with 13.84 mW of peak power at a matched load of 40 MΩ. This work provides guidance for nanofiller choices for high-performance TENG preparation.

Network of Inorganic Nanocrystals Can Swell: Study of Swelling-Induced Surface Instability.

A unique organic-inorganic hybrid network composed of inorganic nanocores (ranging from semiconductors to metallic ones) interconnected through organic molecules can be produced by crosslinking the organic ligands of colloidal inorganic nanocrystals in assemblies. This work reports that this network, which is conventionally considered an inorganic film, can swell when exposed to a solvent because of the interaction between the solvent and the organic linkage within the network. Intriguingly, this work discovers that drying the solvent of the swollen organic-inorganic hybrid network can significantly affect the morphology owing to the swelling-induced compress stress, which is widely observed in various organic network systems. This work studies the surface instability of crosslinked organic-inorganic hybrid networks swollen by various organic solvents, which led to buckling delamination. Specifically, this work investigates the effects of the i) solvent-network interaction, ii) crosslinking density of the network, and iii) thickness of the film on the delamination behavior of the crosslinked network.

Liquid‐Phase Transfer of Organic–Inorganic Halide Perovskite Films for TEM Investigation and Planar Heterojunction Fabrication

AbstractOrganic–inorganic halide perovskites (OIHPs) show high promise in optical and electronic applications such as solar cells, light‐emitting diodes, and nonlinear optics. However, the fundamental knowledge of the atomic‐scale microstructures in OIHP thin films is limited due to the challenge in characterizing them using transmission electron microscopy (TEM). Here a solution‐phase “release‐and‐transfer” method is demonstrated, which entails the lifting of OIHP films from their original substrates while maintaining the film integrity, followed by a sequential transfer onto a TEM grid. The freestanding nature of the OIHP films with a nanoscale thickness, prepared as such, allows a direct TEM observation in the plan view, complementing those typical cross‐sectional views enabled by focus‐ion‐beam specimen fabrication. Using low‐dose scanning TEM, the atomic‐scale microstructure of transferred OIHP films is confirmed to be generally maintained, while the microstrain existing in original films is largely relaxed. This “release‐and‐transfer” method is generic to both standard 3D and low‐dimensional OIHPs. Based on a simple layer‐by‐layer transfer, the fabrication of a 2D–3D planar heterojunction with a good interfacial contact and optoelectronic properties is achieved. This unique methodology offers new opportunities to accelerate the fundamental and practical developments of OIHP materials and devices.