Toward Continuous-Wave Pumped Metal Halide Perovskite Lasers: Strategies and Challenges

One-pot synthesis of heterostructured CsPbBr3/PdSe nanowires with excellent humidity stability

Lead halide perovskite nanowires (NWs) have garnered increasing attention owing to their unique properties, including axial carrier transportation, low pumping thresholds, and polarized emission. However, their intrinsic instability significantly limits their applications. In this study, heterostructured CsPbBr3/PbSe NWs with a diameter of 10 nm and lengths ranging from several to tens of microns were successfully synthesized via a one-pot solution-phase process. Photoluminescence measurements revealed that the CsPbBr3/PbSe NWs emitted green fluorescence with a narrow width of 16 nm and a high photoluminescence quantum yield (PLQY) of 37.6%. The obtained CsPbBr3/PbSe NWs underwent anion exchange with I- ion precursors to transform into CsPbBr3-xIx/PbSe, but not with Cl- ion precursors. Remarkably, these heterostructured CsPbBr3/PbSe NWs remained stable when immersed in water or exposed to air for several months, demonstrating excellent humidity stability. This study offers an effective approach for preparing stable CsPbBr3 NWs and fosters their future applications in optoelectronic devices.

Perovskite Quantum Dots Lasing in Double-Heterostructure through Energy Transfer

Planar double heterostructures were initially investigated and have been successfully applied in III-V semiconductor lasers due to their excellent roles in confining both the photons and carriers. Here, we design and fabricate a (PEA)2Csn-1PbnX3n+1 (quasi-2D)/CsPbBr3 QD/quasi-2D double-heterostructure sandwiched in a 3/2 λ DBR microcavity, and then demonstrate a single-mode pure-green lasing with a threshold of 53.7 μJ/cm2 under nanosecond-pulsed optical pumping. The thresholds of these heterostructure devices decrease statistically by about 50% compared to the control group with no energy donor layers, PMMA/QD/PMMA in an identical microcavity. We show that there is efficient energy transfer from the barrier regions of the quasi-2D phases to the QD layer by transient absorption and luminescence lifetime spectra and that such energy transfer leads to marked threshold reduction. This work indicates that the double-heterostructure configurations should play a significant role in the future perovskite electrically pumped laser.

Metal-Halide Perovskite Lasers: Cavity Formation and Emission Characteristics

Hybrid metal-halide perovskites (MHPs) have shown remarkable optoelectronic properties as well as facile and cost-effective processability. With the success of MHP solar cells and light-emitting diodes, MHPs have also exhibited great potential as gain media for on-chip lasers. However, to date, stable operation of optically pumped MHP lasers and electrically driven MHP lasers-an essential requirement for MHP laser's insertion into chip-scale photonic integrated circuits-is not yet demonstrated. The main obstacles include the instability of MHPs in the atmosphere, rudimentary MHP laser cavity patterning methods, and insufficient understanding of emission mechanisms in MHP materials and cavities. This review aims to provide a detailed overview of different strategies to improve the intrinsic properties of MHPs in the atmosphere and to establish an optimal MHP cavity patterning method. In addition, this review discusses different emission mechanisms in MHP materials and cavities and how to distinguish them.

Nonlinear Boost of Optical Angular Momentum Selectivity by Hybrid Nanolaser Circuits

Selective control of light is essential for optical science and technology, with numerous applications. However, optical selectivity in the angular momentum of light has been quite limited, remaining constant by increasing the incident light power on previous passive optical devices. Here, we demonstrate a nonlinear boost of optical selectivity in both the spin and orbital angular momentum of light through near-field selective excitation of single-mode nanolasers. Our designed hybrid nanolaser circuits consist of plasmonic metasurfaces and individually placed perovskite nanowires, enabling subwavelength focusing of angular-momentum-distinctive plasmonic fields and further selective excitation of nanolasers in nanowires. The optically selected nanolaser with a nonlinear increase of light emission greatly enhances the baseline optical selectivity offered by the metasurface from about 0.4 up to near unity. Our demonstrated hybrid nanophotonic platform may find important applications in all-optical logic gates and nanowire networks, ultrafast optical switches, nanophotonic detectors, and on-chip optical and quantum information processing.

Green Solvent Ethanol-Based Inks for Industrially Applicable Deposition of High-Quality Perovskite Films for Optoelectronic Device Applications

Incontrovertibly there is an increasing demand for the development of benign inks suitable for fabrication of high-performing perovskite-based thin film functional layers. Nevertheless, most reported perovskite precursors rely on the use of highly toxic solvents such as acetonitrile, 2-methoxyethanol, dimethylformamide, and many others. Hence, there is a strong imperative for the development of novel and greener inks, which will facilitate smoother commercialization of technologies based on functional perovskite films. Therefore, four perovskite precursors are studied, some of which consist of up to 90% ethanol. All inks are developed to fulfill the requirements of a high-throughput deposition compatible with roll-to-roll techniques at room temperature, assisted by an air knife for instant solvent removal. Two of the inks are particularly suitable for the fabrication of high-quality and densely packed multi-crystalline (CH3 NH3 )PbI3 layers, as confirmed by numerous nanoscale spectroscopic and material characterization techniques. Additionally, large-area photoluminescence (PL) imaging is demonstrated to improve the quality of the deposited perovskite films, with a route to enhance deposition uniformity when upscaling for manufacture. The genuine potential of the developed greener perovskite inks is demonstrated with the fabrication of solar cells with power conversion efficiencies above 19.5%.

Highly Crystalized MAPbX3 Perovskite Triangular Nanowire Arrays for Optoelectronic Applications

Here, a facile fabrication approach for the high-quality 1D perovskite triangular nanowire (TNW) array synthesis through space-confined effect is reported. A soft stamp containing 1D triangular linear array pattern is used to confine the MAPbX3 solution and to guide the growth of the nanowires along the prescribed direction with good crystallinity. The further constructed photodetectors based on the obtained MAPbI3 TNWs exhibit superior photoresponse properties with a responsivity of (125.2 ± 2.5) A W-1 and detectivity of (2.8 ± 0.8) × 1013 Jones at the wavelength of 650 nm. This excellent performance is attributed to the highly crystalline TNW with optical anisotropy and a small asymptotic height, which reduces the probability of the photon reflection and promotes the carrier transport. More interestingly, the increased surface area of the triangular device can present superior flexibility after a couple of thousands of bending cycles. Furthermore, by fabricating 7 × 7 photodetector arrays, the potential image sensor application is demonstrated. The perovskite nanowire fabrication approach is scalable and compatible with current semiconductor manufacturing, which indicates their great potential in broad applications.

Growth and High-Performance Photodetectors of CsPbBr3 Single Crystals

Organic-inorganic hybrid perovskites have demonstrated exceptional photovoltaic properties, making them highly promising for solar cells and photodetectors (PDs). However, the organic components of these materials are vulnerable to heat and strong light illumination, limiting their application prospects. All-inorganic cesium-based perovskite PDs, on the other hand, possess enhanced thermal tolerance and stability, making them ideal for perovskite applications. The utilization of a ternary mixture solvent and additives in combination with single crystal (SC) growth has enabled the production of highly crystalline SCs with a defect density of 3.79 × 10⁹ cm^-3. The performance of the SC PDs had been evaluated using metal-semiconductor-metal devices, which demonstrated excellent results with a dark current as low as 0.198 μA at 10 V bias, on-off ratios exceeding 10³, and a response time of shorter than 1 ms.

Toward Nonepitaxial Laser Diodes

Thin-film organic, colloidal quantum dot, and metal halide perovskite semiconductors are all being pursued in the quest for a wavelength-tunable diode laser technology that does not require epitaxial growth on a traditional semiconductor substrate. Despite promising demonstrations of efficient light-emitting diodes and low-threshold optically pumped lasing in each case, there are still fundamental and practical barriers that must be overcome to reliably achieve injection lasing. This review outlines the historical development and recent advances of each material system on the path to a diode laser. Common challenges in resonator design, electrical injection, and heat dissipation are highlighted, as well as the different optical gain physics that make each system unique. The evidence to date suggests that continued progress for organic and colloidal quantum dot laser diodes will likely hinge on the development of new materials or indirect pumping schemes, while improvements in device architecture and film processing are most critical for perovskite lasers. In all cases, systematic progress will require methods that can quantify how close new devices get with respect to their electrical lasing thresholds. We conclude by discussing the current status of nonepitaxial laser diodes in the historical context of their epitaxial counterparts, which suggests that there is reason to be optimistic for the future.

Exciton-polariton light-emitting diode based on a single ZnO superlattice microwire heterojunction with performance enhanced by Rh nanostructures

One-dimensional (1D) wirelike superlattice micro/nanostructures have received considerable attention for potential applications due to their versatility and capability for modulating optical and electrical characteristics. In this study, 1D superlattice microwires (MWs), which are made of undoped ZnO and Ga-doped ZnO with periodic and alternating crystalline layers (ZnO/ZnO:Ga), were synthesized individually. Under optical excitation, a series of resonance peaks in the photoluminescence spectrum can be ascribed to polariton emission, which originates from the coupling interaction of the 1D photonic crystal and confined excitons along the wire direction. Using a p-type GaN layer as the hole transport layer, a kind of waveguide light source based on an individual ZnO/ZnO:Ga superlattice MW was proposed and constructed. By analysing the spatially resolved electroluminescence spectra, the observed multipeak was ascribed to exciton-polariton emission with a vacuum Rabi splitting of about 275 meV. Cladding with Rh nanostructures gives rise to appropriate ultraviolet plasmons, and the Rabi splitting energy of our device was enhanced up to 413 meV. The exciton-polariton properties were further examined using angle-resolved electroluminescence measurements. Therefore, individual superlattice MWs can act as optical microresonators to achieve photon-exciton coupling with a large Rabi splitting energy. The experimental results indicate that an individual ZnO/ZnO:Ga superlattice MW can be generally used in developing exciton-polariton luminescence/lasing light sources, particularly for constructing low-threshold/thresholdless lasers toward pragmatic applications.

Temperature-Dependent Amplified Spontaneous Emission in CsPbBr3 Thin Films Deposited by Single-Step RF-Magnetron Sputtering

Due to their high optical efficiency, low-cost fabrication and wide variety in composition and bandgap, halide perovskites are recognized nowadays as real contenders for the development of the next generation of optoelectronic devices, which, among others, often require high quality over large areas which is readily attainable by vacuum deposition. Here, we report the amplified spontaneous emission (ASE) properties of two CsPbBr₃ films obtained by single-step RF-magnetron sputtering from a target containing precursors with variable compositions. Both the samples show ASE over a broad range of temperatures from 10 K up to 270 K. The ASE threshold results strongly temperature dependent, with the best performance occurring at about 50 K (down to 100 µJ/cm²), whereas at higher temperatures, there is evidence of thermally induced optical quenching. The observed temperature dependence is consistent with exciton detrapping up to about 50 K. At higher temperatures, progressive free exciton dissociation favors higher carrier mobility and increases trapping at defect states with consequent emission reduction and increased thresholds. The reported results open the way for effective large-area, high quality, organic solution-free deposited perovskite thin films for optoelectronic applications, with a remarkable capability to finely tune their physical properties.

Lead-free all-inorganic halide double perovskite materials for optoelectronic applications: progress, performance and design

The geometrical and electronic structures of all-inorganic halide double perovskites and their applications in optoelectronic devices are reviewed. Novel design methods are desirable to develop this type of perovskite with superior performance.