CsPbI3 Perovskite Nanocrystals Research Articles

Enhanced environmental stability and luminescence performance of CsPbI3 nanocrystals through SDS passivation and LEuH anchoring

CsPbI3 perovskite nanocrystals (NCs) have been identified as promising candidates for optoelectronic devices due to their low bandgap, wide absorption spectrum, and high color purity. However, their practical applications are limited by their vulnerability to transforming into the yellow non-perovskite phase in ambient conditions. In this study, we propose a novel approach to prepare highly stable black-phase CsPbI3 NCs by passivating them with sodium dodecyl sulfate (SDS) and anchoring them with flower-like layered europium hydroxide (LEuH). The addition of SDS to CsPbI3 NCs plays a crucial role in inhibiting defect formation by preventing the ligand from desorbing. Furthermore, LEuH, with its surface OH– groups, effectively anchors the CsPbI3 NCs onto its nanosheets, preventing their agglomeration. The resulting composite LEuH-SDS-CsPbI3 nanocomposites exhibit extraordinary environmental stability, maintaining their phase structure even after 60 days of storage under ambient conditions. Additionally, their photoluminescence quantum yield reaches an impressive 95 %. The exceptional luminescence performance of the LEuH-SDS-CsPbI3 nanocomposites opens up new possibilities for their application in optoelectronic devices. Furthermore, when used in white LEDs, these nanocomposites exhibit excellent luminescence efficiencies, further highlighting their potential for commercial utilization in the field.

Ligand engineering for improving the stability and optical properties of CsPbI3 perovskite nanocrystals

Inorganic lead halide perovskite nanocrystals (NCs) have recently become one of the research topics for optoelectronic applications due to their excellent photophysical properties. Despite their notable thermal stability over organic-inorganic halide perovskites, CsPbI3 NCs suffer from the phase instability of α-CsPbI3 phase at room temperature and under ambient conditions. Here, the effects of 4-Hydroxybenzoic acid (4-HBA) as an additive to standard oleic acid – oleylamine pair on the stability and optical properties of CsPbI3 perovskite NCs are discussed. 4-HBA addition into perovskite NC systems causes a compressive strain on perovskite lattice, which leads to the formation of a mixed phase α- and γ-CsPbI3 phases while pristine perovskite has α-CsPbI3 phase. Time-dependent stability of the perovskite NCs was tested under an ethanol (EtOH) medium. After EtOH exposure of the perovskite NCs, CsPbI3 NCs transformed to non-perovskite phase in 1 h while 4-HBA added CsPbI3 NCs still have perovskite phase after 48 h. In addition to the improved optical properties of the perovskite NCs, 4-HBA addition remarkably improves CsPbI3 perovskite stability.

Fabricating Solid‐Solution‐Type Perovskite/Fluoride Nanocomposites Through Sublattice Interlocking for High‐Performance Photovoltaics

AbstractAll‐inorganic α‐phase CsPbI3 perovskite with a suitable bandgap and superb optoelectronic properties is transforming the landscape of perovskite photovoltaics, but its long‐term lability associated with “soft” ionic lattice still imposes a great challenge for practical applications. Herein, a unique solid‐solution fluorination strategy is proposed to deliver an “ideal” perovskite matrix of α‐phase CsPbI3 abundant with F ions through interlocking the soft lattice of CsPbI3 with cubic‐phase CsF·3/2HF. Such a sublattice interlocking can not only stabilize the soft lattice of α‐phase CsPbI3 perovskite nanocrystals but also passivate their notorious surface defects, thereby producing a “rigid” solid‐solution‐type perovskite/fluoride CsPbI3/CsF (termed as CsPbI3:F) nanocomposite with excellent long‐term stability and a near‐unity photoluminescence efficiency. Of particular note is that these CsPbI3:F nanocomposites can work well as effective grain boundary anchors to significantly improve the photovoltaic performance of perovskite solar cells because of their F‐rich perovskite lattice, achieving a T80 stability of 1500 h under continuous maximum power point tracking and AM 1.5G illumination without the need for encapsulation. This work paves a new way to deliver perovskite materials with desirable properties for photovoltaics.

Pure-red electroluminescence of quantum-confined CsPbI3 perovskite nanocrystals obtained by the gradient purification method

Pure-red emission light-emitting diodes (LEDs) are highly desirable for display and lighting applications. Here, we present a synergistic approach to fabricate pure-red emission LEDs based on quantum-confined CsPbI3 nanocrystals (NCs). By introducing ZnI2 acting as a co-precursor and passivating agent into the synthesis, and applying a gradient post-synthesis purification method allowing us to obtain size-selected fractions with precisely adjusted emission colors, we obtained uniform and small (about 6 nm), quantum-confined CsPbI3 NCs exhibiting high stability in ambient conditions and a superior photoluminescence quantum yield of up to 88%. These NCs exhibited the tendency to undergo oriented attachment, resulting in self-assembled superstructures with a pure-red emission at 629 nm. Importantly, partial recrystallization into fused superstructures led to removal of the insulating ligand barriers between NCs. LEDs based on the CsPbI3 NCs showed pure-red electroluminescence at 633 nm, with an external quantum efficiency of 14.7% and a luminance of over 1000 cd/m2. Our study reveals the mechanism behind the oriented attachment and assembly of small, quantum-confined CsPbI3 NCs, and contributes to the development of pure-red electroluminescent LEDs.

Enrichment of anchoring sites by introducing supramolecular halogen bonds for the efficient perovskite nanocrystal LEDs

Considering the multi-functionalization of ligands, it is crucial for ligand molecular design to reveal the landscape of anchoring sites. Here, a typical triphenylphosphine (TPP) ligand was employed to explore its effect on the surface of CsPbI3 perovskite nanocrystals (PNCs). Except for the conventionally considered P-Pb coordination, an P-I supramolecular halogen bonding was also found on the NC surface. The coexistence of the above two types of bonding significantly increased the formation energy of iodine vacancy defects and improved the photoluminescence quantum yield of PNCs up to 93%. Meanwhile, the direct interaction of P and I enhanced the stability of the Pb-I octahedra and dramatically inhibited the migration of I ions. Furthermore, the introduction of additional benzene rings (2-(Diphenylphosphino)-biphenyl (DPB)) increased the delocalized properties of the PNC surface and significantly improved the charge transport of the PNCs. As a result, the DPB passivated CsPbI3 NCs based top-emitting LEDs exhibite a peak external quantum efficiency (EQE) of 22.8%, a maximum luminance of 15, 204 cd m−2, and an extremely low-efficiency roll-off of 2.6% at the current density of 500 mA cm−2.

Efficient Ligand Passivation Enables Ultrastable CsPbX3 Perovskite Nanocrystals in Fully Alcohol Environments

AbstractHalide perovskite nanocrystals (PNCs) have demonstrated their wide potential to fabricate efficient optoelectronic devices and to prepare promising photocatalysts for solar‐driven photo(electro)chemical reactions. However, their use in most of the practical applications is limited due to the instability of PNCs in polar environments. Here, the preparation of non‐encapsulated CsPbX3 nanocrystals dispersed in fully alcohol environments, with outstanding stability through surface defect passivation strategy is reported. By using didodecyldimethylammonium bromide (DDAB) during material post‐treatment, highly luminescent CsPbBr3 PNCs with remarkable stability in methanol/butanol medium up to 7 months with near‐unity photoluminescence quantum yield are achieved. This approach is extrapolated to stabilize iodine‐based CsPbBr3‐xIx and CsPbI3 PNCs, showing an improvement of their photoluminescence features and stability in these high polar alcohols up to 6 h. DDAB mediates the defect suppression through ligand exchange and avoids the full permeation of alcohol to be in contact with the PNCs. In this context, DDAB induces ionization of alcohol molecules to strengthen the surface passivation. The findings open the door to the development of long‐term stable CsPbX3 PNCs with high optical performance to be used in polar environments.

Synthesis and optical properties of CsPbI3 perovskite nanocrystals in borosilicate glass doped with Nd3+ ions

We investigated the optical properties of the borosilicate glass matrix system doped with Nd3+ ions and incorporated with CsPbI3 nanocrystals, produced by the fusion method. The energy transfer process from CsPbI3 nanocrystals to Nd3+ ions was analyzed from optical absorption and photoluminescence spectra overlap. Transmission electron microscopy images show that the nanocrystals grown in the borosilicate glass matrix had an average size of 9.5 nm and interplanar distances of d015 = 0.280 nm, which corresponds to the CsPbI3 semiconductor. X-ray diffraction (XRD) and selected area of electron diffraction (SAED) patterns show the peaks associated with the (015) and (020) planes, characteristic of the orthorhombic crystal structure. An emission band was observed at 888 nm (transition 4F3∕2 → 4I9∕2) under excitation of 532 nm, attributed by the Nd3+ ion, in which the photoluminescence lifetime as a function of temperature (296 to 600 K) was obtained.

Enhanced Spontaneous Emission of CsPbI3 Perovskite Nanocrystals Using a Hyperbolic Metamaterial Modified by Dielectric Nanoantenna.

In this work, we demonstrate, theoretically and experimentally, a hybrid dielectric-plasmonic multifunctional structure able to provide full control of the emission properties of CsPbI3 perovskite nanocrystals (PNCs). The device consists of a hyperbolic metamaterial (HMM) composed of alternating thin metal (Ag) and dielectric (LiF) layers, covered by TiO2 spherical MIE nanoresonators (i.e., the nanoantenna). An optimum HMM leads to a certain Purcell effect, i.e., an increase in the exciton radiative rate, but the emission intensity is reduced due to the presence of metal in the HMM. The incorporation of TiO2 nanoresonators deposited on the top of the HMM is able to counteract such an undesirable intensity reduction by the coupling between the exciton and the MIE modes of the dielectric nanoantenna. More importantly, MIE nanoresonators result in a preferential light emission towards the normal direction to the HMM plane, increasing the collected signal by more than one order of magnitude together with a further increase in the Purcell factor. These results will be useful in quantum information applications involving single emitters based on PNCs together with a high exciton emission rate and intensity.

Spectral properties of CsPbX3 (X=Br, I) perovskite nanocrystals in borogermanate glass-ceramics

Pure CsPbBr3 and CsPbI3 perovskite nanocrystals are nucleated in the borogermanate glass. Nanocrystals precipitation in glass are controlled via isothermal treatment at temperatures above Tg by adjusting the temperature and duration starting from 15 min. X-ray diffraction data and optical measurements have confirmed the formation of 5–8 nm sized CsPbBr3 nanocrystals and 6–15 nm sized CsPbI3 nanocrystals. Wherein, the photoluminescence of lead cesium bromide perovskite is tuned in the 490–530 nm range, and the luminescence of iodide perovskite is changed in the 640–740 nm range. The maximum luminescence quantum yield of pure CsPbI3 perovskites is 19%. Water, climate and acid resistance tests show borogermanate glasses with perovskite nanocrystals are compatible with commercial dense crowns.

Efficient and Stable Blue- and Red-Emitting Perovskite Nanocrystals through Defect Engineering: PbX2 Purification

Current efforts to reduce the density of structural defects such as surface passivation, doping, and modified synthetic protocols have allowed us to grow high-quality perovskite nanocrystals (PNCs). However, the role of the purity of the precursors involved during the PNC synthesis to hinder the emergence of defects has not been widely explored. In this work, we analyzed the use of different crystallization processes of PbX2 (X = Cl– or I–) to purify the chemicals and produce highly luminescent and stable CsPbCl3–xBrx and CsPbI3 PNCs. The use of a hydrothermal (Hyd) process to improve the quality of the as-prepared PbCl2 provides blue-emitting PNCs with efficient ligand surface passivation, a maximum photoluminescence quantum yield (PLQY) of ∼ 88%, and improved photocatalytic activity to oxidize benzyl alcohol, yielding 40%. Then, the hot recrystallization of PbI2 prior to Hyd treatment led to the formation of red-emissive PNCs with a PLQY of up to 100%, long-term stability around 4 months under ambient air, and a relative humidity of 50–60%. Thus, CsPbI3 light-emitting diodes were fabricated to provide a maximum external quantum efficiency of up to 13.6%. We claim that the improvement of the PbX2 crystallinity offers a suitable stoichiometry in the PNC structure, reducing nonradiative carrier traps and so maximizing the radiative recombination dynamics. This contribution gives an insight into how the manipulation of the PbX2 precursor is a profitable and potential alternative to synthesize PNCs with improved photophysical features by making use of defect engineering.

Mg2+-Assisted Passivation of Defects in CsPbI3 Perovskite Nanocrystals for High-Efficiency Photoluminescence.

CsPbI3 perovskite nanocrystals (NCs) are emerging as promising materials for optoelectronic devices because of their superior optical properties. However, the poor stability of CsPbI3 NCs has become a huge bottleneck for practical applications. Herein, we report an effective strategy of Mg2+-assisted passivation of surface defects to obtain high emission efficiency and stability in CsPbI3 NCs. It is found that the introduced Mg2+ ions are mainly distributed on the surface of NCs and then passivate the NC defects, enhancing radiative decay rate and reducing nonradiative decay rate. As a result, the as-prepared Mg2+-treated CsPbI3 (Mg-CsPbI3) NCs exhibit the highest photoluminescence quantum yield (PLQY) of 95%. The Mg-CsPbI3 NC colloidal solution retains 80% of its original PLQY after 80 days of atmosphere exposure. The red perovskite light-emitting diodes based on the Mg-CsPbI3 NCs demonstrate an external quantum efficiency of 8.4%, which shows an almost 4-fold improvement compared to the devices based on the untreated NCs.

Improving the stability and optical properties of CsPbI3 perovskite nanocrystals by 1-Octadecanethiol through surface modification

As traditional capping ligands like oleic acid (OA) and oleylamine (OLA) cannot efficiently maintain the optoelectronic properties and stability of iodide perovskite nanocrystals (NCs), post synthesis surface modification with some other ligand is a convenient and valid method to solve these problems to some extent. Here we promote a long carbon chain ligand with a thiol group, 1-Octadecanethiol (ODT), to realize the passivation of the surface of CsPbI3 NCs after the synthesis process. After modification, our ODT-CsPbI3 NCs exhibit excellent optical properties with a high PLQY of 93% and outstanding stability under different conditions compared to the untreated samples.

Homogeneous and inhomogeneous broadening in single perovskite nanocrystals investigated by micro-photoluminescence

Metal halides with perovskite crystalline structure have given rise to efficient optoelectronic and photonic devices. In the present work, we have studied the light emission properties of single CsPbBr3 and CsPbI3 semiconductor perovskite nanocrystals (PNCs), as the basis for a statistical analysis of micro-photoluminescence (micro-PL) spectra measured on tens of them. At room temperature, the linewidth extracted from PL spectra acquired in dense films of these nanocrystals is not very different from that of micro-PL measured in single nanocrystals. This means that the homogeneous linewidth due to exciton-phonon interaction is comparable or larger than the inhomogeneous effect associated to the micro-PL peak energy dispersion due to the nanocrystal size distribution defined by the chemical synthesis of the PNCs. Contrarily, we observe very narrow micro-PL lines in CsPbBr3 and CsPbI3 PNCs at 4 K, in the range of 1–5 meV and 0.1–0.5 meV, respectively, because they are limited by spectral diffusion. Aging of PNCs under ambient conditions has been also studied by micro-PL and a clear reduction of their nanocube edge size in the order of the nm/day is deduced.

2.5–5.5 μm mid‐infrared emission from Ni2+‐doped chalcohalide glass ceramics containing CsPbI3 perovskite nanocrystals

AbstractThe development of mid‐infrared (MIR) broadband tunable lasers urgently needs high performance laser gain materials. Transition metal (TM) ions doped glass ceramics are considered to be efficient MIR broadband laser gain media. However, it is difficult to achieve gain because of the large scattering loss and low luminescence efficiency. In this paper, GeS2–Sb2S3–CsI–PbI2 chalcohalide glass ceramics containing CsPbI3 perovskite nanocrystals are fabricated by the melt‐quenching method and subsequent heating treatment. The crystallization behavior of CsPbI3 nanophase and MIR luminescence properties of Ni2+ dopant are systematically investigated. Evidently, spherical CsPbI3 perovskite nanocrystals are precipitated and uniformly distributed in the glassy matrix, which can reduce the light scattering and make the chalcohalide glass ceramics have a high transparency. Moreover, an ultra‐broadband MIR emission in the range of 2.5–5.5 μm is observed for the first time, to our best knowledge, from Ni2+‐doped chalcohalide glass ceramics containing CsPbI3 perovskite nanocrystals. The newly developed Ni2+‐doped chalcohaldie glass ceramics could be promising gain media for MIR broadband tunable lasers.

Effect of Capping Ligand Engineering on Transport Properties and Carrier Dynamics in Cubic CsPbI3 Nanocrystal Film

Cubic (α) phase CsPbI3 perovskite nanocrystals (NCs) are highly sought-after solar cell materials due to their appropriate bandgap of 1.73 eV. Nevertheless, the NCs are capped by insulating organic...

Highly Luminescent and Stable CsPbI3 Perovskite Nanocrystals with Sodium Dodecyl Sulfate Ligand Passivation for Red-Light-Emitting Diodes.

CsPbI3 perovskite nanocrystals (NCs) have recently emerged as promising materials for optoelectronic devices because of their superior properties. However, the poor stability of the CsPbI3 NCs induced by easy ligand desorption represents a key issue limiting their practical applications. Herein, we report stable and highly luminescent black-phase CsPbI3 NCs passivated by novel ligands of sodium dodecyl sulfate (SDS). Theoretical calculation results reveal a stronger adsorption energy of SDS molecules at the CsPbI3 surface than that of commonly used oleic acid. As a result, the defect formation caused by the ligand loss during the purification process is greatly suppressed. The optimized SDS-CsPbI3 NCs exhibit significantly reduced surface defects, much enhanced stability, and superior photoluminescence efficiency. The red perovskite light-emitting diodes based on the SDS-CsPbI3 NCs demonstrate an external quantum efficiency of 8.4%, which shows a 4-fold improvement compared to the devices based on the oleic acid-modified CsPbI3 NCs.

Critical role of additive-induced molecular interaction on the operational stability of perovskite light-emitting diodes

Summary Despite rapid improvements in efficiency and brightness of perovskite light-emitting diodes (PeLEDs), the poor operational stability remains a critical challenge hindering their practical applications. Here, we demonstrate greatly improved operational stability of high-efficiency PeLEDs, enabled by incorporating dicarboxylic acids into the precursor for perovskite depositions. We reveal that the dicarboxylic acids efficiently eliminate reactive organic ingredients in perovskite emissive layers through an in situ amidation process, which is catalyzed by the alkaline zinc oxide substrate. The formed stable amides prohibit detrimental reactions between the perovskites and the charge injection layer underneath, stabilizing the perovskites and the interfacial contacts and ensuring the excellent operational stability of the resulting PeLEDs. Through rationally optimizing the amidation reaction in the perovskite emissive layers, we achieve efficient PeLEDs with a peak external quantum efficiency of 18.6% and a long half-life time of 682 h at 20 mA cm−2, presenting an important breakthrough in PeLEDs.

Ni2+-doped CsPbI3 perovskite nanocrystals with near-unity photoluminescence quantum yield and superior structure stability for red light-emitting devices

Room temperature phase instability of cubic CsPbI3 perovskite nanocrystals is one of the notorious limitations for practical applications in optoelectronic fields. Herein, the incorporation of Ni2+ ions into CsPbI3 lattice was successfully achieved by a modified hot-injection method using nickel acetate as doping precursor. The as-prepared Ni2+ (3.3 mol%): CsPbI3 nanocrystals exhibited an improved, near-unity (95%~100%) photoluminescence quantum yield owing to the enhanced radiative decay rate and the decreased non-radiative decay rate. Additionally, Ni-doping was demonstrated to stabilize CsPbI3 lattice and the Ni2+: CsPbI3 film and colloidal solution can retain their red luminescence up to 15 days and 7 months in atmosphere, respectively. First-principle calculations verified that the significantly improved optical performance and stability of Ni2+: CsPbI3 nanocrystals arose primarily from the increased formation energy due to the successful doping of Ni2+ in CsPbI3. Benefiting from such an effective doping strategy, the as-prepared Ni2+-doped CsPbI3 perovskite nanocrystals can function well as efficient red-light emitter toward the fabrication of high-performance perovskite LED with a peak external quantum efficiency of ~7%.

Enhanced thermal stability of exciton recombination in CsPbI3 perovskite nanocrystals via zinc alloying

In this work, the Pb2+ substitution with Zn2+ in CsPbI3 perovskite nanocrystals (PNCs) is partially achieved to improve the optoelectronic properties through temperature-pressure assisted crystallization approach. The spectral and dynamic exciton recombination for zinc alloyed CsPbI3 PNCs are probed with steady-state/time-resolved PL (TRPL), transient absorption (TA) techniques. Compared with pure CsPbI3 PNCs, PLQY can be boosted to 60% when incorporating the optimal amount of ZnI2 in the synthesis, and long-term thermal stability are obtained in a series of red-emitting alloyed CsPbI3 PNCs. Simultaneously, the change of exciton binding energy and average optical phonon energy indicate that weaker nonradiative transition for exciton recombination of zinc alloyed CsPbI3 PNCs than those of CsPbI3 PNCs. TRPL and TA spectroscopy are used to understand the photoinduced carrier relaxation processes. The carrier dynamics reveal that the coupling between Zn-induced lowest excited state and exciton trapping state is promoted in zinc alloyed CsPbI3 PNCs, which can significantly enhance the efficiency of excitonic recombination. The improved performance of PLQY and thermal stability makes these zinc alloyed CsPbI3 PNCs as appropriate perovskite materials for efficient optoelectronic devices.

Carrier Multiplication and Hot-Carrier Cooling Dynamics in Quantum-Confined CsPbI3 Perovskite Nanocrystals.

Carrier multiplication (CM) is an effective mechanism that makes it possible to use hot carriers (HCs) to bypass the Shockley-Queisser limit for solar-cell efficiency. In this paper, we present a detailed study of both CM and HC cooling dynamics in quantum-confined CsPbI3 perovskite nanocrystals (NCs), using femtosecond transient absorption spectroscopy. Our results show that barrierless CM, with an efficiency exceeding 90%, can be achieved in strongly confined NCs on a time scale of ≪200 fs. A low CM efficiency (∼40%), however, is observed in weakly confined NCs. HC cooling dynamics suggests the absence of an intrinsic phonon bottleneck in strongly confined NCs. Furthermore, the biexciton Auger rate increased 4-fold in strongly confined NCs compared to that in weakly confined NCs. These results suggest that the enhanced CM in strongly confined NCs likely originates from enhanced Coulomb coupling and relaxed momentum conservation.