Slow‐Photon‐Effect‐Induced Photoelectrical‐Conversion Efficiency Enhancement for Carbon‐Quantum‐Dot‐Sensitized Inorganic CsPbBr3 Inverse Opal Perovskite Solar Cells

All‐inorganic cesium lead halide perovskite is suggested as a promising candidate for perovskite solar cells due to its prominent thermal stability and comparable light absorption ability. Designing textured perovskite films rather than using planar‐architectural perovskites can indeed optimize the optical and photoelectrical conversion performance of perovskite photovoltaics. Herein, for the first time, this study demonstrates a rational strategy for fabricating carbon quantum dot (CQD‐) sensitized all‐inorganic CsPbBr₃ perovskite inverse opal (IO) films via a template‐assisted, spin‐coating method. CsPbBr₃ IO introduces slow‐photon effect from tunable photonic band gaps, displaying novel optical response property visible to naked eyes, while CQD inlaid among the IO frameworks not only broadens the light absorption range but also improves the charge transfer process. Applied in the perovskite solar cells, compared with planar CsPbBr₃, slow‐photon effect of CsPbBr₃ IO greatly enhances the light utilization, while CQD effectively facilitates the electron–hole extraction and injection process, prolongs the carrier lifetime, jointly contributing to a double‐boosted power conversion efficiency (PCE) of 8.29% and an increased incident photon‐to‐electron conversion efficiency of up to 76.9%. The present strategy on CsPbBr₃ IO to enhance perovskite PCE can be extended to rationally design other novel optoelectronic devices.     

Low‐Voltage Photodetectors with High Responsivity Based on Solution‐Processed Micrometer‐Scale All‐Inorganic Perovskite Nanoplatelets

All‐inorganic photodetectors based on scattered CsPbBr₃ nanoplatelets with lateral dimension as large as 10 µm are fabricated, and the CsPbBr₃ nanoplatelets are solution processed governed by a newly developed ion‐exchange soldering mechanism. Under illumination of a 442 nm laser, the photoresponsivity of photodetectors based on these scattered CsPbBr₃ nanoplatelets is as high as 34 A W^?1, which is the largest value reported from all‐inorganic perovskite photodetectors with an external driven voltage as small as 1.5 V. Moreover, the rise and fall times are 0.6 and 0.9 ms, respectively, which are comparable to most of the state‐of‐the‐art all‐inorganic perovskite‐based photodetectors. All the material synthesis and device characterization are conducted at room temperature in ambient air. This work demonstrates that the solution‐processed large CsPbBr₃ nanoplatelets are attractive candidates to be applied in low‐voltage, low‐cost, ultra highly integrated optoelectronic devices.     

Controllable Growth of Aligned Monocrystalline CsPbBr3 Microwire Arrays for Piezoelectric‐Induced Dynamic Modulation of Single‐Mode Lasing

CsPbBr₃ shows great potential in laser applications due to its superior optoelectronic characteristics. The growth of CsPbBr₃ wire arrays with well‐controlled sizes and locations is beneficial for cost‐effective and largely scalable integration into on‐chip devices. Besides, dynamic modulation of perovskite lasers is vital for practical applications. Here, monocrystalline CsPbBr₃ microwire (MW) arrays with tunable widths, lengths, and locations are successfully synthesized. These MWs could serve as high‐quality whispering‐gallery‐mode lasers with high quality factors (>1500), low thresholds (<3 µJ cm^?2), and long stability (>2 h). An increase of the width results in an increase of the laser quality and the resonant mode number. The dynamic modulation of lasing modes is achieved by a piezoelectric polarization‐induced refractive index change. Single‐mode lasing can be obtained by applying strain to CsPbBr₃ MWs with widths between 2.3 and 3.5 µm, and the mode positions can be modulated dynamically up to ≈9 nm by changing the applied strain. Piezoelectric‐induced dynamic modulation of single‐mode lasing is convenient and repeatable. This method opens new horizons in understanding and utilizing the piezoelectric properties of lead halide perovskites in lasing applications and shows potential in other applications, such as on‐chip strain sensing.     

Aqueous Phase Exfoliating Quasi‐2D CsPbBr3 Nanosheets with Ultrahigh Intrinsic Water Stability

All‐inorganic cesium lead halide perovskite nanocrystals (NCs) have emerged as attractive optoelectronic materials due to the excellent optical and electronic properties. However, their environmental stability, especially in the presence of water, is still a significant challenge for their further commercialization. Here, ultrahigh intrinsically water‐stable all‐inorganic quasi‐2D CsPbBr₃ nanosheets (NSs) via aqueous phase exfoliation method are reported. Compared to conventional perovskite NCs, these unique quasi‐2D CsPbBr₃ nanosheets present an outstanding long‐term water stability with 87% photoluminescence (PL) intensity remaining after 168 h under water conditions. Moreover, the photoluminescence quantum yields (PLQY) of quasi‐2D CsPbBr₃ NSs is up to 82.3%, and these quasi‐2D CsPbBr₃ NSs also present good photostability of keeping 85% PL intensity after 2 h under 365 nm UV light. Evidently, such quasi‐2D perovskite NSs will open up a new way to investigate the intrinsic stability of all‐inorganic perovskites and further promote the commercial development of perovskite‐based optoelectronic and photovoltaic devices.     

A Microchannel-Confined Crystallization Strategy Enables Blade Coating of Perovskite Single Crystal Arrays for Device Integration

Perovskite single crystals (PSCs) possess superior optoelectronic properties compared to their corresponding polycrystalline films, but their applications of PSCs in high-performance, integrated devices are hindered by their heavy thickness and difficulty in scalable deposition. Here, a microchannel-confined crystallization (MCC) strategy to grow uniform and large-area PSC arrays for integrated device applications is reported. Benefiting from the confinement effect of the microchannels, solution flow dynamics is well controlled, and thus uniform deposition of PSC arrays with suitable thickness is achieved, meaning they are applicable for scale-up device applications. The resulting PSCs possess excellent optoelectronic properties in terms of a long carrier lifetime (175 ns) and an ultralow defect density (2 × 10⁹ cm⁻³), which are comparable to the corresponding bulk crystals. The unique embedded structure of PSCs within the microchannels allows the construction of a high-integration image sensor. This work paves the way toward high-throughput growth of PSCs for integrated optoelectronic devices.     

Dual‐Phase CsPbBr3–CsPb2Br5 Perovskite Thin Films via Vapor Deposition for High‐Performance Rigid and Flexible Photodetectors

Inorganic perovskites with special semiconducting properties and structures have attracted great attention and are regarded as next generation candidates for optoelectronic devices. Herein, using a physical vapor deposition process with a controlled excess of PbBr₂, dual‐phase all‐inorganic perovskite composite CsPbBr₃–CsPb₂Br₅ thin films are prepared as light‐harvesting layers and incorporated in a photodetector (PD). The PD has a high responsivity and detectivity of 0.375 A W^?1 and 10¹¹ Jones, respectively, and a fast response time (from 10% to 90% of the maximum photocurrent) of ≈280 µs/640 µs. The device also shows an excellent stability in air for more than 65 d without encapsulation. Tetragonal CsPb₂Br₅ provides satisfactory passivation to reduce the recombination of the charge carriers, and with its lower free energy, it enhances the stability of the inorganic perovskite devices. Remarkably, the same inorganic perovskite photodetector is also highly flexible and exhibits an exceptional bending performance (>1000 cycles). These results highlight the great potential of dual‐phase inorganic perovskite films in the development of optoelectronic devices, especially for flexible device applications.     

Phase Transition Control for High Performance Ruddlesden–Popper Perovskite Solar Cells

Ruddlesden–Popper reduced‐dimensional hybrid perovskite (RDP) semiconductors have attracted significant attention recently due to their promising stability and excellent optoelectronic properties. Here, the RDP crystallization mechanism in real time from liquid precursors to the solid film is investigated, and how the phase transition kinetics influences phase purity, quantum well orientation, and photovoltaic performance is revealed. An important template‐induced nucleation and growth of the desired (BA)₂(MA)₃Pb₄I₁₃ phase, which is achieved only via direct crystallization without formation of intermediate phases, is observed. As such, the thermodynamically preferred perpendicular crystal orientation and high phase purity are obtained. At low temperature, the formation of intermediate phases, including PbI₂ crystals and solvate complexes, slows down intercalation of ions and increases nucleation barrier, leading to formation of multiple RDP phases and orientation randomness. These insights enable to obtain high quality (BA)₂(MA)₃Pb₄I₁₃ films with preferentially perpendicular quantum well orientation, high phase purity, smooth film surface, and improved optoelectronic properties. The resulting devices exhibit high power conversion efficiency of 12.17%. This work should help guide the perovskite community to better control Ruddlesden–Popper perovskite structure and further improve optoelectronic and solar cell devices.     

Effect of sulfur-doped graphene quantum dots incorporation on morphological,optical and electron transport properties of CH3NH3PbBr3 perovskite thin films

Organic–inorganic hybrid perovskite materials have recently attracted extensive interest to develop next-generation high efficiency optoelectronic devices. However, in many of these devices, perovskite thin films are the key source of photogenerated electron and hole pairs. Therefore, a strategy for the preparation of high-quality perovskite thin films with a fewer number of traps at surfaces and grain boundaries is highly desired. In this work, sulfur-doped graphene quantum dots (S-GQDs) were synthesized and incorporated in the CH₃NH₃PbBr₃ perovskite precursor to prepare S-GQDs incorporated perovskite thin films. The as-prepared thin films were systematically characterized using X-ray diffractometer, field emission scanning electron microscope, UV–Vis and fluorescence spectrophotometer to investigate the effect of different amounts of S-GQDs on their morphology, optical absorbance and electron transfer properties. The experimental findings revealed that multiple surface functional groups, quantum confinement and desirable electronic conductivity in S-GQDs help passivate the perovskite surface by reducing the surface and grain boundary traps. Interestingly, the incorporation of S-GQDs increased the light absorption of CH₃NH₃PbBr₃ along with faster electron transfer across their interfaces. Hence, this strategy of S-GQDs incorporation presents a versatile and novel way to prepare highly efficient perovskite thin films for developing next-generation solar cells, light emitting diodes and other optoelectronic devices.

     

Spontaneous Self‐Assembly of Perovskite Nanocrystals into Electronically Coupled Supercrystals: Toward Filling the Green Gap

Self‐assembly of nanoscale building blocks into ordered nanoarchitectures has emerged as a simple and powerful approach for tailoring the nanoscale properties and the opportunities of using these properties for the development of novel optoelectronic nanodevices. Here, the one‐pot synthesis of CsPbBr₃ perovskite supercrystals (SCs) in a colloidal dispersion by ultrasonication is reported. The growth of the SCs occurs through the spontaneous self‐assembly of individual nanocrystals (NCs), which form in highly concentrated solutions of precursor powders. The SCs retain the high photoluminescence (PL) efficiency of their NC subunits, however also exhibit a redshifted emission wavelength compared to that of the individual nanocubes due to interparticle electronic coupling. This redshift makes the SCs pure green emitters with PL maxima at ≈530–535 nm, while the individual nanocubes emit a cyan‐green color (≈512 nm). The SCs can be used as an emissive layer in the fabrication of pure green light‐emitting devices on rigid or flexible substrates. Moreover, the PL emission color is tunable across the visible range by employing a well‐established halide ion exchange reaction on the obtained CsPbBr₃ SCs. These results highlight the promise of perovskite SCs for light emitting applications, while providing insight into their collective optical properties.     

Flexible and Self-Powered Photodetector Arrays Based on All-Inorganic CsPbBr3 Quantum Dots

Flexible devices are garnering substantial interest owing to their potential for wearable and portable applications. Here, flexible and self-powered photodetector arrays based on all-inorganic perovskite quantum dots (QDs) are reported. CsBr/KBr-mediated CsPbBr₃ QDs possess improved surface morphology and crystallinity with reduced defect densities, in comparison with the pristine ones. Systematic material characterizations reveal enhanced carrier transport, photoluminescence efficiency, and carrier lifetime of the CsBr/KBr-mediated CsPbBr₃ QDs. Flexible photodetector arrays fabricated with an optimum CsBr/KBr treatment demonstrate a high open-circuit voltage of 1.3 V, responsivity of 10.1 A W⁻¹, specific detectivity of 9.35 × 10¹³ Jones, and on/off ratio up to ≈10⁴. Particularly, such performance is achieved under the self-powered operation mode. Furthermore, outstanding flexibility and electrical stability with negligible degradation after 1600 bending cycles (up to 60°) are demonstrated. More importantly, the flexible detector arrays exhibit uniform photoresponse distribution, which is of much significance for practical imaging systems, and thus promotes the practical deployment of perovskite products.     

Stabilizing perovskite nanocrystals by controlling protective surface ligands density

After nanocrystals synthesis, the purification process with anti-solvents is an essential step to get clean nanocrystals, which could get rid of the by-products of the synthesis. It is generally recognized that this process could bring a positive effect for the afterward optoelectronic applications. Unfortunately, we found that the optical properties and photostability of perovskite CsPbBr₃ nanocrystals were unavoidably deteriorated after they were washed with anti-solvents, and this deterioration is strongly related to the decreasing of surface ligands density. Therefore, in this paper, we tried to purposely not wash the CsPbBr₃ nanocrystals solution after adding didodecyl dimethylammonium bromide (DDAB), and found the existing of DDAB in solution could result in a dramatically enhanced photostability. Inspired by these results, we proposed a new strategy to stabilize perovskite nanocrystals from the view of packaging process: adding protective ligands into the perovskite nanocrystals resin directly, then encapsulating them on blue light-emitting diodes (LED) chips. Surprisingly, stable LED devices (20 mA, 2.7V) were achieved by this way, which can keep 80% of the initial photoluminescence (PL) intensity for more than 50 h, while the devices with CsPbBr₃ nanocrystals without adding protective ligands into resin dropped to 50% of their initial PL intensity within 6 h. This approach offers a new thought to stabilize perovskite nanocrystals as down-conversion phosphor in quantum dots liquid crystal display.

     

Imbedded Nanocrystals of CsPbBr3 in Cs4PbBr6: Kinetics,Enhanced Oscillator Strength,and Application in Light‐Emitting Diodes

Solution‐grown films of CsPbBr₃ nanocrystals imbedded in Cs₄PbBr₆ are incorporated as the recombination layer in light‐emitting diode (LED) structures. The kinetics at high carrier density of pure (extended) CsPbBr₃ and the nanoinclusion composite are measured and analyzed, indicating second‐order kinetics in extended and mainly first‐order kinetics in the confined CsPbBr₃, respectively. Analysis of absorption strength of this all‐perovskite, all‐inorganic imbedded nanocrystal composite relative to pure CsPbBr₃ indicates enhanced oscillator strength consistent with earlier published attribution of the sub‐nanosecond exciton radiative lifetime in nanoprecipitates of CsPbBr₃ in melt‐grown CsBr host crystals and CsPbBr₃ evaporated films.     

Superior Self‐Powered Room‐Temperature Chemical Sensing with Light‐Activated Inorganic Halides Perovskites

Hybrid halide perovskite is one of the promising light absorber and is intensively investigated for many optoelectronic applications. Here, the first prototype of a self‐powered inorganic halides perovskite for chemical gas sensing at room temperature under visible‐light irradiation is presented. These devices consist of porous network of CsPbBr₃ (CPB) and can generate an open‐circuit voltage of 0.87 V under visible‐light irradiation, which can be used to detect various concentrations of O₂ and parts per million concentrations of medically relevant volatile organic compounds such as acetone and ethanol with very quick response and recovery time. It is observed that O₂ gas can passivate the surface trap sites in CPB and the ambipolar charge transport in the perovskite layer results in a distinct sensing mechanism compared with established semiconductors with symmetric electrical response to both oxidizing and reducing gases. The platform of CPB‐based gas sensor provides new insights for the emerging area of wearable sensors for personalized and preventive medicine.     

Direct Growth of Perovskite Crystals on Metallic Electrodes for High‐Performance Electronic and Optoelectronic Devices

Metal halide perovskite has attracted enhanced interest for its diverse electronic and optoelectronic applications. However, the fabrication of micro‐ or nanoscale crystalline perovskite functional devices remains a great challenge due to the fragility, solvent, and heat sensitivity of perovskite crystals. Here, a strategy is proposed to fabricate electronic and optoelectronic devices by directly growing perovskite crystals on microscale metallic structures in liquid phase. The well‐contacted perovskite/metal interfaces ensure these heterostructures serve as high‐performance field effect transistors (FETs) and excellent photodetector devices. When serving as an FET, the on/off ratio is as large as 10⁶ and the mobility reaches up to ≈2.3 cm² V^?1 s^?1. A photodetector is displayed with high photoconductive switching ratio of ≈10⁶ and short response time of ≈4 ms. Furthermore, the photoconductive response is proved to be band‐bending‐assisted separation of photoexcited carriers at the Schottky barrier of the silver and p‐type perovskites.     

All-inorganic dual-phase halide perovskite nanorings

In the present work, we report the growth of all-inorganic perovskite nanorings with dual compositional phases of CsPbBr₃ and CsPb₂Br₅ via a facile hot injection process. The self-coiling of CsPbBr₃-CsPb₂Br₅ nanorings is driven by the axial stress generated on the outside surface of the as-synthesized nanobelts, which results from the lattice mismatch during the transformation of CsPbBr₃ to CsPb₂Br₅. The tailored growth of nanorings could be achieved by adjusting the key experimental parameters such as reaction temperature, reaction time and stirring speed during the cooling process. The photoluminescence intensity and quantum yield of nanorings are higher than those of CsPbBr₃ nanobelts, accompanied by a narrower full width at half maximum (FWHM), suggesting their high potential for constructing self-assembled optoelectronic nanodevices.

     

Crystallization Kinetics and Morphology Control of Formamidinium–Cesium Mixed‐Cation Lead Mixed‐Halide Perovskite via Tunability of the Colloidal Precursor Solution

The meteoric rise of the field of perovskite solar cells has been fueled by the ease with which a wide range of high‐quality materials can be fabricated via simple solution processing methods. However, to date, little effort has been devoted to understanding the precursor solutions, and the role of additives such as hydrohalic acids upon film crystallization and final optoelectronic quality. Here, a direct link between the colloids concentration present in the [HC(NH₂)₂]_0.83Cs_0.17Pb(Br_0.2I_0.8)₃ precursor solution and the nucleation and growth stages of the thin film formation is established. Using dynamic light scattering analysis, the dissolution of colloids over a time span triggered by the addition of hydrohalic acids is monitored. These colloids appear to provide nucleation sites for the perovskite crystallization, which critically impacts morphology, crystal quality, and optoelectronic properties. Via 2D X‐ray diffraction, highly ordered and textured crystals for films prepared from solutions with lower colloidal concentrations are observed. This increase in material quality allows for a reduction in microstrain along with a twofold increase in charge‐carrier mobilities leading to values exceeding 20 cm² V^?1 s^?1. Using a solution with an optimized colloidal concentration, devices that reach current–voltage measured power conversion efficiency of 18.8% and stabilized efficiency of 17.9% are fabricated.     

Nanocube Superlattices of Cesium Lead Bromide Perovskites and Pressure‐Induced Phase Transformations at Atomic and Mesoscale Levels

Lead halide perovskites are promising materials for a range of applications owing to their unique crystal structure and optoelectronic properties. Understanding the relationship between the atomic/mesostructures and the associated properties of perovskite materials is crucial to their application performances. Herein, the detailed pressure processing of CsPbBr₃ perovskite nanocube superlattices (NC‐SLs) is reported for the first time. By using in situ synchrotron‐based small/wide angle X‐ray scattering and photoluminescence (PL) probes, the NC‐SL structural transformations are correlated at both atomic and mesoscale levels with the band‐gap evolution through a pressure cycle of 0 ? 17.5 GPa. After the pressurization, the individual CsPbBr₃ NCs fuse into 2D nanoplatelets (NPLs) with a uniform thickness. The pressure‐synthesized perovskite NPLs exhibit a single cubic crystal structure, a 1.6‐fold enhanced photoluminescence quantum yield, and a longer emission lifetime than the starting NCs. This study demonstrates that pressure processing can serve as a novel approach for the rapid conversion of lead halide perovskites into structures with enhanced properties.     

Perovskite single crystals: Dimensional control,optoelectronic properties,and applications

Lead halide perovskite single crystals have emerged as promising candidates for high-performance optoelectronic devices because of their superior optoelectronic properties. To date, much literature has reported the fabrication of various perovskite single-crystal structures. However, it still lacks effective rationalization and a comprehensive understanding of the relationship between the structural characteristics and functional properties of the perovskite single crystals, which is of great significance for fabricating perovskite single crystals-based high-performance optoelectronic devices. In this review, we give a comprehensive overview of the synthesis of perovskite single crystals with diverse dimensions, including 0D perovskite quantum dots (QDs), 1D micro/nanowires, 2D micro/nanoplates and single-crystal thin films (SCTFs), and 3D micro/nanoscale single-crystal structures. The relationship between the dimensional structure and properties of the perovskite single crystals is discussed in detail. Dimensional requirements for different optoelectronic applications are systematically summarized. Finally, perspectives on remaining challenges and future opportunities are highlighted.     

Highly luminescent and stable CsPbBr3 perovskite quantum dots modified by phosphine ligands

All-inorganic cesium lead halide perovskite quantum dots (QDs) have been a promising candidate for optoelectronic devices in recent years, such as light-emitting diodes, photodetectors and solar cells, owing to their superb optoelectronic properties. Still, the stability issue of nanocrystals is a bottleneck for their practical application. Herein, we report a facile method for the synthesis of a series of phosphine ligand modified CsPbBr₃ QDs with high PL intensity. By introducing organic phosphine ligands, the tolerance of CsPbBr₃ QDs to ethanol, water and UV light was dramatically improved. Moreover, the phosphine ligand modified QD films deposited on the glass subtracts exhibit superior PL intensity and optical stability to those of pristine QD based films.

     

A Strategy for Architecture Design of Crystalline Perovskite Light‐Emitting Diodes with High Performance

All present designs of perovskite light‐emitting diodes (PeLEDs) stem from polymer light‐emitting diodes (PLEDs) or perovskite solar cells. The optimal structure of PeLEDs can be predicted to differ from PLEDs due to the different fluorescence dynamics and crystallization between perovskite and polymer. Herein, a new design strategy and conception is introduced, “insulator–perovskite–insulator” (IPI) architecture tailored to PeLEDs. As examples of FAPbBr₃ and MAPbBr₃, it is experimentally shown that the IPI structure effectively induces charge carriers into perovskite crystals, blocks leakage currents via pinholes in the perovskite film, and avoids exciton quenching simultaneously. Consequently, as for FAPbBr₃, a 30‐fold enhancement in the current efficiency of IPI‐structured PeLEDs compared to a control device with poly(3,4ethylenedioxythiophene):poly(styrene sulfonate) as hole‐injection layer is achieved—from 0.64 to 20.3 cd A^?1—while the external quantum efficiency is increased from 0.174% to 5.53%. As the example of CsPbBr₃, compared with the control device, both current efficiency and lifetime of IPI‐structured PeLEDs are improved from 1.42 and 4 h to 9.86 cd A^?1 and 96 h. This IPI architecture represents a novel strategy for the design of light‐emitting didoes based on various perovskites with high efficiencies and stabilities.