Lead-free Perovskite Nanocrystals Research Articles

Lead-Free Perovskite Nanocrystals Decorating Graphene for Detecting Nerve Agents

Lead-Free Perovskite Nanocrystals Decorating Graphene for Detecting Nerve Agents

Lead-free metal–halide perovskite nanocrystals: synthesis and optical properties [Review

Subject of study. Lead-free perovskite nanocrystals (LFPNCs), their main characteristics, synthesis methods, and optical properties are examined. Aim of study. The aim is to analyze the state-of-the-art research data on the synthesis methods and optical properties of LFPNCs. In addition, the formation processes of LFPNCs, their main synthesis methods, and the dependence of nanocrystal size and photoluminescence quantum yield (PLQY) on synthesis parameters (such as method, temperature, and ligand type) are determined. Main results. The formation of LFPNCs is analyzed based on the LaMer and cluster growth models. According to the research data, the primary methods for preparing these nanocrystals (NCs) are hot-injection and ligand-assisted reprecipitation (LARP). Evidently, the average size of LFPNCs increases with increasing reaction temperature. For NCs synthesized by LARP, increasing the reaction temperature to 100°C leads to a slight decrease in the quantum yield. However, for the NCs prepared by hot-injection, the PLQY remains independent of the temperature. Additionally, using oleic acid as a ligand results in a narrow size distribution of NCs, whereas using a mixture of ligands results in NCs exhibiting the highest PLQY. Practical significance. The literature analysis results show that the LARP method is the most promising for synthesizing LFPNCs owing to its ease of implementation, energy efficiency, and scalability. The LFPNCs produced using this method can be applied as active materials in sensor technologies, photovoltaics, and optoelectronic devices.

Blue emitting fluorescent Cs2ZnCl4 perovskite nanoprobe for the sensing and visual detection of bilirubin-a jaundice biomarker

Lead halide perovskites are an advanced class of materials with high photoluminescence and optoelectronic properties. However their instability towards moisture and lead toxicity hinders their applications especially in biological sensing. Hence the need for novel lead free perovskite nanocrystals are of utmost important. Herein we synthesized a lead free, highly efficient, stable, cost effective Cs2ZnCl4 perovskite nanocrystals (PNCs) and extends its application in biosensing. The PNCs exhibits bright blue fluorescence upon UV irradiation and was able to selectively detect bilirubin (BR) - a clinically important jaundice biomarker. The intense fluorescence emission of the sensor was completely quenched upon the addition of bilirubin. The sensor could detect bilirubin even in the presence of other interfering biomolecules with a good limit of detection of 26.10 nM. The sensor could successively detect BR in human serum samples. Furthermore, for the visual detection of bilirubin, a paper strip sensor was also designed making the sensor more economical and adaptable.

Modeling and performance investigation of novel inorganic Cs4CuSb2Cl12 nanocrystal perovskite solar cell using SCAPS-1D

For the next generation of photovoltaic devices, perovskite solar cells (PSCs) appear as a good choice because they are simple and convert energy to electricity very efficiently. Recent years have seen a great deal of interest in organic-inorganic lead halide perovskites due to their exceptional optoelectronic properties. Nonetheless, additional commercialization of the Pb element is still restricted by its inevitable toxicity. To address the instability and toxicity of the lead hybrid perovskite, it is imperative to produce entirely inorganic lead-free perovskite nanocrystals. Cs4CuSb2Cl12 offers promising qualities and strong stability against light, heat, and humidity to overcome these drawbacks. It possesses an efficient photo-generated carrier and good carrier mobility. In this study, a lead-free perovskite solar cell with the novel configuration of FTO/WS2/Cs4CuSb2Cl12/CuSbS2/Ni has been optimized using SCAPS-1D simulation software and investigates the potential of Cs4CuSb2Cl12 nanocrystal solar cell. The impact of different characteristics of charge transport materials on Cs4CuSb2Cl12 nanocrystal solar cells has been reported. Additionally, the study computationally optimizes the thickness of perovskite layer, doping concentration, defect density, and other input parameters to propose an effective PSC with power conversion efficiency of 23.10 %, Voc of 1.1675V, and FF of 83.33 %.

Tuneable Efficient White Emission of Sb3+/Mn2+ Co-Doped Lead-Free Perovskites for Single-Component White Light-Emitting Diodes.

Inorganic lead-free perovskite nanocrystals (NCs) with broadband self-trapped exciton (STEs) emission and low toxicity have shown enormous application prospects in the field of display and lighting. However, white light-emitting diodes (WLEDs) based on a single-component material with high photoluminescence quantum yield (PLQY) remain challenging. Here, we demonstrate a novel codoping strategy by introducing Sb3+/Mn2+ ions to achieve the tuneable dual emission in lead-free perovskite Cs3InCl6 NCs. The PLQY increases to 59.64% after doping with Sb3+. The codoped Cs3InCl6 NCs exhibit efficient white light emission due to the energy transfer channel from STEs to Mn2+ ions with PLQY of 51.38%. Density functional theory (DFT) calculations have been used to verify deeply the effects of Sb3+/Mn2+ doping. WLEDs based on Sb3+/Mn2+-codoped Cs3InCl6 NCs are explored with color rendering index of 85.5 and color coordinate of (0.398, 0.445), which have been successfully applied as photodetector lighting sources. This work provides a new perspective for designing novel lead-free perovskites to achieve single-component WLEDs.

Simultaneously excited downshifting/upconversion luminescence from lanthanide-doped core–shell lead-free perovskite nanocrystals for encryption and data storage

The constructed Cs2AgInCl6-based core–shell NCs with separated optically active centers can not only prevent the adverse energy interactions between dopants, but also achieve dual-modal PL in the visible region and improved photostability.

Lattice doping of lanthanide ions in Cs2ZrCl6 nanocrystals enabling phase transition and tunable photoluminescence.

Dopants can endow lead-free perovskite nanocrystals with novel photoelectric properties. However, understanding the effect of dopants on the structure and energy transfer of lead-free perovskite nanocrystals remains limited. In this work, we synthesize zero-dimensional Cs2ZrCl6 nanocrystals with a blue light quantum yield of up to 75.6% by an improved hot-injection method. And we introduce trace amounts of lanthanide ions (Ln3+) (<∼8%) in the lattice of nanocrystals and establish an effective energy transfer channel from self-trapped excitons (STEs) to various Ln3+ ions (Tb3+, Eu3+, Dy3+, Sm3+, and Pr3+), which can achieve tunable photoluminescence between red, green and blue. Interestingly, with increasing Ln3+ concentrations (>∼10%), the phase transition from the cubic phase Cs2ZrCl6:Ln3+ to the monoclinic phase Cs3LnCl6:Zr4+ occurred, while Zr4+ ions began to act as dopants. And a new energy transfer channel from dopant [ZrCl6]2- to host Ln3+ ions was established in the Cs3LnCl6 host accompanied by enhanced broadband photoluminescence excitation (PLE) and photoluminescence (PL). In particular, the photoluminescence quantum yield (PLQY) of Tb3+ ions increases from 0.77% to 54% upon the phase transition (under 276 nm excitation). Our study provides new insights into the effects of dopants on the structure of perovskite nanocrystals and is beneficial to the design of a variety of light-emitting materials for optoelectronic applications.

Highly efficient, self-powered UV photodiodes based on leadfree perovskite nanocrystals through interfacial engineering

Double perovskite crystals are promising alternatives for lead-based perovskites that has potential to address toxicity and instability issues. In this study, Cs2AgBiCl6 nanocrystals (NCs) with high absorption coefficients were synthesized by hot-injection method. The bandgap engineering was realized by tuning the halide composition in Cs2AgBiCl6 to Cs2AgBiBr6. Both NCs were used as light-absorbing layers in lead-free perovskite photodiodes that exhibit wavelength-selectivity for UV–visible light operatable even at a bias voltage of 0 V. Cs2AgBiBr6-based photodiode exhibits a characteristic detection peak at 340 nm with a responsivity of 3.21 mA W−1, a specific detectivity up to 8.91 × 1010 Jones and a fast response speed with a rise/fall time of 30/35 ms. The excellent performance of self-driven photodiodes lights up the prospect of lead-free perovskite NCs in highly efficient optoelectronic devices.

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

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

Multicolor emission from lanthanide ions doped lead-free Cs3Sb2Cl9 perovskite nanocrystals

The toxicity of lead ions has become the severe challenge for the all-inorganic lead halide perovskite materials, although some works have reported the lead-free perovskite nanocrystals (NCs), the photoluminescence quantum yield (PLQY) of these materials is still unsatisfactory. Meanwhile, because the halogen ions can be easily exchanged, the controllable multicolor emission in perovskite NCs is difficult to realize in current reports. In this work, we introduced lanthanide ions into lead-free Cs3Sb2Cl9 perovskite NCs. Benefitting from the energy transfer between Cs3Sb2Cl9 perovskite NC host and lanthanide ions, the multicolor emission was realized. Based on controlling the doping concentration of Tb3+ and Eu3+ ions, the white light emission under UV excitation would be turned easily in the Tb3+/Eu3+ codoped NCs. In addition, efficient energy transfer from perovskite NCs to Tb3+ or Eu3+ ions is beneficial to improving the optical properties of lead-free perovskite NCs, resulting in maximum PLQYs of red, green and white light emission of 22.6%, 19.7% and 28.5%, respectively. Finally, a white light emitting device (WLED) was fabricated with a power efficiency of 18.5 lm/W, which presents the Commission Internationale de l’Eclairage (CIE) of (0.33, 0.35).

Phase transition and rapid temperature response of lead-free perovskite Cs–Cu–I nanocrystals enabled by their size

Reducing the amount of Cs-oleate can reduce the size of Cs3Cu2I5 lead-free perovskite nanocrystals from 22 to 10 nm. The as-obtained nanocrystals show a more uniform size distribution and a more rapid response to temperature change of only 15 s.

Unraveling the Gas-Sensing Mechanisms of Lead-Free Perovskites Supported on Graphene.

Lead halide perovskites have been attracting great attention due to their outstanding properties and have been utilized for a wide variety of applications. However, the high toxicity of lead promotes an urgent and necessary search for alternative nanomaterials. In this perspective, the emerging lead-free perovskites are an environmentally friendly and harmless option. The present work reports for the first time gas sensors based on lead-free perovskite nanocrystals supported on graphene, which acts as a transducing element owing to its high and efficient carrier transport properties. The use of nanocrystals enables achieving excellent sensitivity toward gas compounds and presents better properties than those of bulky perovskite thin films, owing to their quantum confinement effect and exciton binding energy. Specifically, an industrially scalable, facile, and inexpensive synthesis is proposed to support two different perovskites (Cs3CuBr5 and Cs2AgBiBr6) on graphene for effectively detecting a variety of harmful pollutants below the threshold limit values. H2 and H2S gases were detected for the first time by utilizing lead-free perovskites, and ultrasensitive detection of NO2 was also achieved at room temperature. In addition, the band-gap type, defect tolerance, and electronic surface traps at the nanocrystals were studied in detail for understanding the differences in the sensing performance observed. Finally, a comprehensive sensing mechanism is proposed.

Ultrafast Dynamics of Self-Trapped Excitons in Lead-Free Perovskite Nanocrystals.

Lead-free halide perovskite nanocrystals (NCs) have received increasing attention owing to their low toxicity and high stability. Localized charge distribution and strong carrier-phonon coupling in lead-free perovskite NCs facilitates the formation of self-trapped excitons (STEs), which typically give a broadband photoluminescence (PL) emission with a large Stokes shift. In this Perspective, we highlight how PL modulations can give rise to an efficient white-light emission by understanding and tuning the ultrafast dynamics of STEs in lead-free perovskite NCs. We then present the exciton energy transfer mediated by STEs to provide an efficient thermally activated delayed fluorescence and dopant PL. We also illustrate promising directions for future applications based on STEs. We hope that this Perspective can provide a new viewpoint for researchers to understand the ultrafast dynamics of STEs and promote lead-free perovskite NCs for optoelectronic applications.

Slow carrier relaxation in tin-based perovskite nanocrystals

The conversion efficiency of solar energy in semiconductors is fundamentally limited by ultrafast hot-carrier relaxation processes, and slowing down these processes is critical for improved energy harvesting. Here we report formamidinium tin iodide (FASnI3) nanocrystals where quantum confinement effects yield an evolution from a continuous band structure to separate energy states with decreasing nanocrystal size, as observed by transient absorption spectroscopy. The appearance of separate energy levels slows down the relaxation of hot carriers by two orders of magnitude at low injected carrier densities (<1 carrier pair per nanoparticle). The observed build up time of the ground-state bleach at the band edge is two orders of magnitude slower in FASnI3 nanocrystals than in lead halide perovskite bulk and nanocrystals, which we attribute to a phonon bottleneck effect. Our results highlight the promise of lead-free perovskite nanocrystals for high-efficiency photovoltaic applications operating above the Shockley–Queisser limit. Tin-based perovskite nanocrystals with slower than usual relaxation dynamics holds promise for superior lead-free perovskite optoelectronic devices.

Graphene-Based Gas Sensor Loaded with Lead-Free Perovskite Nanocrystals

Introduction Semiconducting devices based on graphene show outstanding potential due to their mechanical, electronic and chemical properties. However, the development of commercial graphene-based gas sensors is still challenging due to significant drawbacks that should be overcome. For instance, pristine graphene shows poor sensitivity and selectivity towards gas molecules, which makes necessary its modification/functionalisation. Sensing performance can be improved using different strategies such as the decoration of graphene with metal oxide nanoparticles. However, the use of metal oxides generally involves operating the sensor well above room temperature, thus increasing power consumption and reducing the lifetime of the sensor due to aging.Therefore, new research efforts have been focused towards the development of graphene loaded with alternative nanomaterials. Recently, perovskite nanocrystals have been identified as a promising option due to their superior sensitivity and selectivity, combined with their capability to work under room temperature conditions. However, the use of perovskites in gas sensing has been limited due to their degradation when exposed to ambient moisture, hindering its potential application under real conditions. Nevertheless, we demonstrated for the first time a stable gas sensor (over 6 months) based on graphene loaded with a lead halide perovskite (MAPbBr3), even when operated under atmospheres with a significant level of moisture [1]. The reason is that the hydrophobic character of the graphene protects the perovskite nanocrystals against their degradation in humid environments.More recently, we studied the role of the anions and cations in the gas sensing mechanism towards volatile organic compounds (VOCs) [2]. Considering the perovskite formula (ABX3), we synthesized several nanocrystals by changing the cation A (MA, FA and Cs) and the anion X (Br, I and Cl). However, the use of lead in these perovskites induces potential risks to human health and the environment. For that reason, graphene loaded with lead-free perovskites has been developed here to reduce the potential risks associated with the manipulation of lead and to assess the new sensing properties by replacing the cation B. Method Lead-free perovskite nanocrystals (Cs3Cu2Br5) have been synthesized through a hot injection method. Afterwards, the graphene nanoflakes have been loaded with Cs3Cu2Br5 via impregnation technique. Once a homogeneous perovskite distribution was achieved, the nanocomposite was deposited via spray pyrolysis onto alumina substrates with platinum screen-printed electrodes. The gas sensors were placed in an airtight testing chamber connected to an automated gas mixture and delivery system. The gas sensing properties were studied under dry and humid conditions. Characterization Several characterisation techniques were employed to analyse the nanomaterials synthesised. The crystalline structure of lead-free perovskite was evaluated through X-Ray Diffraction (XRD), while X-Ray Photoelectron Microscopy (XPS) was performed to graphene nanoflakes to analyse the carbon configuration (sp2 and sp3 ratio) and to study the presence of different oxygen functional groups. High-Resolution Transmission Electron Microscopy (HR-TEM) was used to assess size and interplanar distances in perovskite nanocrystals. Additionally, the spatial distribution of perovskites over the graphene nanoflakes was evaluated via a Field Emission Scanning Electron Microscope (FESEM). Finally, the sensing properties of the sensitive hybrid film have been assessed. Results and Conclusions The as-synthesized Cs3Cu2Br5 perovskite nanocrystals show high crystallinity and an average size of a few nanometres. Furthermore, NO2 detection at room temperature has been demonstrated to be sensitive and reproducible (Figure 1). Preliminary measurements using this lead-free perovskite show responses to NO2 about 3-fold higher than those registered for graphene loaded with MAPbBr3 nanocrystals reported in [1]. This nanomaterial has been demonstrated as a feasible option to work at room temperature. Room temperature operation translates into low-power consumption and enhanced sensor lifetime, since high operating temperatures usually involve non-reversible changes in the crystalline structure of nanomaterials. Besides, the well-known instability of perovskites in the presence of relative humidity is overcome thanks to the protective character of graphene-based due to its high hydrophobicity. The combination of these two nanomaterials in the same composite allows taking advantage of the outstanding properties of both, graphene nanoflakes and perovskite nanocrystals. Therefore, gases can be detected at trace levels in a few minutes by using low-cost and low-power sensors.However, the use and manipulation of lead presents additional dangerousness, e.g. at the synthesis of perovskites or at disposal of sensors, which might put at risk human health and the environment. For that reason, the development of a graphene-based gas sensor loaded with lead-free perovskites constitutes a step forward to achieve more sustainable chemoresistors, linked to the concept of green chemistry. Furthermore, once the effect of the cation A and the anion X was assessed, this novel approach will provide a deep understanding about the role of cation B in the sensing mechanisms.

Progresses on Novel B‐Site Perovskite Nanocrystals

AbstractHalide perovskite materials have emerged as a new type of optoelectronic materials serving as key active layer for next‐generation photovoltaics, light‐emitting diodes, lasers, and photodetectors. Manipulating the crystal size toward the so‐called perovskite nanocrystals (PNCs) will endow new properties due to quantum confinement and ligand effect. However, like their bulk crystalline film, the lead toxicity is still one of decisive concerns that holds‐back their public acceptance. Design of lead‐free (LF) PNCs requires efforts on replacing the B‐site element with other metal candidates from the periodic table. In the past half‐decade, hundreds of new LF PNCs have been developed with various sizes, subdimensionalities, ligands, and electron/quantum confinements, as well as wide applications. Although the lead‐based perovskites still dominate the ongoing research fields, the LF PNCs can have a large potential if novel nonlead B‐site element is introduced to render new type of LF PNCs material that is more stable, less toxic, and more efficient in device performance. In this review, recent progresses on the LF PNCs are revisited to seek these opportunities. The paper is organized in subtopics on material structures, synthesis, properties, and their state‐of‐the‐art applications of different LF PNCs, coupled with an in‐depth discussion on the perspectives and challenges.

The Role Silver Nanoparticles Plays in Silver-Based Double-Perovskite Nanocrystals.

Lead-free double perovskites are studied as an optional replacement to lead halide perovskites in optoelectronic applications. Recently, double-perovskite materials in which two divalent lead cations are replaced with an Ag+ and a trivalent cation have been demonstrated. The presence of a reactive silver cation and observations of metallic silver nanodecorations raised concerns regarding the stability and applicability of these materials. To better understand the nucleation and crystal growth of lead-free double perovskites, we explore the origin and role that metallic silver nanoparticles (NPs) play in the Ag-based Pb-free double-perovskite nanocrystal (NC) systems such as Cs2AgInCl6, Cs2AgSbCl6, Cs2AgBiCl6, and Cs2AgBiBr6. With major focus on Cs2AgInCl6 NCs, we show evidence supporting growth of the NCs through heterogeneous nucleation on preexisting metallic silver seeds. The silver seeds nucleate prior to injection of halide through reduction of the Ag+ ion by the aminic ligand. The presence of preexisting silver NPs is supported by a localized surface plasmon resonance (LSPR). The injection of halide precursor into the reaction mixture step initiates a fast nucleation and growth of the perovskite NC on the silver seed. The change in the dielectric medium at the interface of the silver NP results in a quantifiable red shift of the LSPR peak. In addition, we demonstrate charge transfer from the perovskite to the silver NP through photoinduced electrochemical Ostwald ripening of the silver NPs via UV irradiation. The ripened perovskite–metal hybrid nanocrystal exhibits modified optical properties in the form of quenched emission and enhanced plasmonic absorption. Future development of Ag-based double-perovskite NC applications depends on the ability to control Ag+ reduction at all synthetic stages. This understanding is critical for delivering stability and functionality for silver-based lead-free perovskite nanocrystals.

Development of structure and tuning ability of the luminescence of lead-free halide perovskite nanocrystals (NCs)

Halide perovskites have swiftly been elevated to a subject worthy of serious and extensive research. They are unequivocally an unprecedented class of semiconductors with a broad range of optoelectronic applications. These materials display outstanding properties, which are the results of their direct and tunable band gap, high electron/hole mobility, strong light-absorption coefficient, and high defect tolerance coupled with low non-radiative recombination rates. Their preparation is also extremely easy and compatible with room-temperature deposition processes. Nonetheless, the toxic nature of lead (Pb and its ions) and the poor stability against moisture, limit their mass production and commercialization. This article thoroughly reviews the recent investigations undertaken to solve these thorny problems by focusing mainly on the structural development and the photoluminescence tuning ability of lead-free perovskite nanocrystals (NCs). In the light of the principles related to crystal chemistry, we present the development of perovskite NCs from mineral prototypes, which leads to a variety of multi component Pb2+-free perovskite type compounds. Then, assuming that the ultimate goal is the production of a single-component white-light emission device, we shed light on the development of broadly tunable Pb2+-free perovskite NCs with intrinsic emission as well as extrinsic emission achieved by doping with various ions, and on the corresponding energy transfer (ET) mechanism, which governs the color and the photoluminescence emission tuning ability. The present review aims to assist the research which deals with the discovery of new highly stable, nontoxic perovskite NCs, following a strategy associated with excitonic luminescence enhancement, in conjunction with a comprehensive understanding of the role of energy transfer phenomenon, whereby efficient tuning ability is achieved by various dopants

B-Site Co-Alloying with Germanium Improves the Efficiency and Stability of All-Inorganic Tin-Based Perovskite Nanocrystal Solar Cells.

Colloidal lead‐free perovskite nanocrystals have recently received extensive attention because of their facile synthesis, the outstanding size‐tunable optoelectronic properties, and less or no toxicity in their commercial applications. Tin (Sn) has so far led to the most efficient lead‐free solar cells, yet showing highly unstable characteristics in ambient conditions. Here, we propose the synthesis of all‐inorganic mixture Sn‐Ge perovskite nanocrystals, demonstrating the role of Ge2+ in stabilizing Sn2+ cation while enhancing the optical and photophysical properties. The partial replacement of Sn atoms by Ge atoms in the nanostructures effectively fills the high density of Sn vacancies, reducing the surface traps and leading to a longer excitonic lifetime and increased photoluminescence quantum yield. The resultant Sn‐Ge nanocrystals‐based devices show the highest efficiency of 4.9 %, enhanced by nearly 60 % compared to that of pure Sn nanocrystals‐based devices.

Can perovskite inspired bismuth halide nanocrystals outperform their lead counterparts?

In the quest for finding non-toxic and stable lead-free perovskite nanocrystals (NCs), bismuth halide perovskites (BHP) have emerged as a promising alternative. This perspective presents an overview, challenges, and future opportunities in BHP NCs.