HCOO- Doping-Induced Multiexciton Emissions in Cs3Cu2I5 Crystals for Efficient X-Ray Scintillation.

Self-trapped exciton (STE) luminescence, typically associated with structural deformation of excited states, has attracted significant attention in metal halide materials recently. However, the mechanism of multiexciton STE emissions in certain metal halide crystals remains largely unexplored. This study investigates dual luminescence emissions in HCOO- doped Cs3Cu2I5 single crystals using transient and steady-state spectroscopy. The dual emissions are attributed to intrinsic STE luminescence originating from the host lattice and extrinsic STE luminescence induced by external dopants, respectively, each of which can be triggered independently at distinct energy levels. Theoretical calculations reveal that multiexciton emission originates from structural distortion of the host and dopant STEs within the 0D lattice in their respective excited states. By meticulously tuning the excitation wavelength and selectively exciting different STEs, the dynamic alteration of color change in Cs3Cu2I5:HCOO- crystals is demonstrated. Ultimately, owing to an extraordinarily high photoluminescence quantum yield (99.01%) and a diminished degree of self-absorption in Cs3Cu2I5:HCOO- crystals, they exhibit remarkable X-ray scintillation characteristics with light yield being improved by 5.4 times as compared to that of pristine Cs3Cu2I5 crystals, opening up exciting avenues for achieving low-dose X-ray detection and imaging.

Melt blending crystallization regulating balanced nanodomains in efficient and scalable coating processed organic solar cells.

The miscibility between active layer donors (D) and acceptors (A) is a key factor impeding the development of organic photovoltaics (OPVs) toward higher performance and large-area production. In this study, melt blending crystallization (MBC) was used to accomplish molecular-level blending and highly oriented crystallization in bulk heterojunction (BHJ) films realized by a scalable blade coating process, which increased the D/A contact area and provided sufficient exciton diffusion and dissociation. At the same time, the highly organized and balanced crystalline nanodomain structures permitted dissociated carriers to be efficiently transmitted and collected, resulting in significantly enhanced short-circuit current density, fill factor, and efficiency of the device by means of optimum melting temperature and quenching rates. The method can be simply incorporated into current efficient OPV material systems and achieve a device performance comparable to the best values. The blade-coating-processed PM6/IT-4F MBC devices achieved an efficiency of 13.86% in a small-area device and 11.48% in a large-area device. A power conversion efficiency (PCE) of 17.17% was obtained in PM6:BTP-BO-4F devices, and a PCE of 16.14% was acquired in PM6:Y6 devices.

Detector-grade perovskite single-crystal wafers via stress-free gel-confined solution growth targeting high-resolution ionizing radiation detection.

Solution-processed organic‒inorganic halide perovskite (OIHP) single crystals (SCs) have demonstrated great potential in ionizing radiation detection due to their outstanding charge transport properties and low-cost preparation. However, the energy resolution (ER) and stability of OIHP detectors still lag far behind those of melt-grown inorganic perovskite and commercial CdZnTe counterparts due to the absence of detector-grade high-quality OIHP SCs. Here, we reveal that the crystallinity and uniformity of OIHP SCs are drastically improved by relieving interfacial stress with a facial gel-confined solution growth strategy, thus enabling the direct preparation of large-area detector-grade SC wafers up to 4 cm with drastically suppressed electronic and ionic defects. The resultant radiation detectors show both a small dark current below 1 nA and excellent baseline stability of 4.0 × 10-8 nA cm-1 s-1 V-1, which are rarely realized in OIHP detectors. Consequently, a record high ER of 4.9% at 59.5 keV is achieved under a standard 241Am gamma-ray source with an ultralow operating bias of 5 V, representing the best gamma-ray spectroscopy performance among all solution-processed semiconductor radiation detectors ever reported.

Electrically conductive hybrid organic crystals as flexible optical waveguides.

Hybrid materials capitalize on the properties of individual materials to attain a specific combination of performance assets that is not available with the individual components alone. We describe a straightforward approach to preparation of sandwich-type hybrid dynamic materials that combine metals as electrically conductive components and polymers as bending, momentum-inducing components with flexible organic crystals as mechanically compliant and optically transducive medium. The resulting hybrid materials are conductive to both electricity and light, while they also respond to changes in temperature by deformation. Depending on the metal, their conductivity ranges from 7.9 to 21.0 S µm‒1. The elements respond rapidly to temperature by curling or uncurling in about 0.2 s, which in one typical case corresponds to exceedingly fast deformation and recovery rates of 2187.5° s‒1 and 1458.3° s‒1, respectively. In cyclic operation mode, their conductivity decreases less than 1% after 10,000 thermal cycles. The mechanothermal robustness and dual functionality favors these materials as candidates for a variety of applications in organic-based optics and electronics, and expands the prospects of application of organic crystals beyond the natural limits of their dynamic performance.

Highly Stable and Moisture-Immune Monocomponent White Perovskite Phosphor by Trifluoromethyl (-CF3) Regulation.

Halide perovskites are emerging as promising candidates for white light solid state lighting. Nevertheless, there are still challenges of a high water stability, a tunable color temperature, and a high photoluminescence quantum yield (PLQY). Herein, we report hydrophobic, electron-withdrawing trifluoromethyl (-CF3)-modified phenethylamine lead bromide (PEA2PbBr4) with ultrahigh stability in water for >2 months, and the broadband white light emission is illustrated by self-trapped excitons attributed to exciton-phonon coupling that coordinate molecular vibration, lattice distortion, and electrostatic interaction. In particular, by Mn2+ doping, the emission color can be tuned from cold (10237 K) to warm (2406 K), and a greatly enhanced PLQY of ≤87.93% can be achieved. Furthermore, the perovskites also possess an excellent color rendering index (the highest is 94). A monocomponent white light-emitting diode with amazing CIE 1931 coordinates of (0.33, 0.32) is further assembled, demonstrating a luminance of 471.5 cd m-2 at 50 mA and good long-term operation stability after >2 months. This study of highly efficient and stable perovskites with high-quality white light emission will open up new opportunities in solid state lighting.

Thermal Shock Fabrication of Ion-Stabilized Perovskite and Solar Cells.

A highly crystalline tempered-glass-like perovskite grain structure with compressed surface lattice realized by a thermal-shocking fabrication is shown. The strained perovskite grain structure is stabilized by Cl- -reinforcing surface lattice and shows enhanced bonding energy and ionic activation temperature, which contributes to hysteresis-free operation of perovskite solar cells (PSCs) at much higher temperature up to 363 K in thermal-shocking-processed MAPbClx I3- x (T-MPI). The PSCs can be fabricated by a high-speed fully air process without post-annealing based on the scalable bar-coating technique. Both high efficiency and stability are achieved in T-MPI PSC with a power conversion efficiency (PCE) up to 22.99% and long-term operational stability with T80 lifetime exceeding 4000 h.

Thermochromic Cs2 AgBiBr6 Single Crystal with Decreased Band Gap through Order-Disorder Transition.

Lead-free Cs2 AgBiBr6 double perovskite is considered to be a promising alternative to the traditional lead-based analogues due to its long carrier lifetime, high structural stability, and non-toxicity. However, the large band gap limits its absorption of visible light, which is not conducive to further optoelectronic applications. Herein, a thermochromic strategy is reported to decrease the band gap of Cs2 AgBiBr6 by approximately 0.36 eV, obtaining the smallest reported band gap of 1.69 eV under ambient conditions. The experimental data indicate that after annealing the Cs2 AgBiBr6 single crystals at 400 °C, the silver (Ag) and bismuth (Bi) atoms occupy the B-site in a random way and form a partially disordered configuration. The formation of the antisite defects broadens the band edges and decreases the band gap. This work offers new insights into the preparation of narrow band gap lead-free double perovskites, and a deep understanding of their structural and electronic properties for further development in photoelectric devices.

Hydration Intermediate Phase Regulated In-Plane and Out-Plane Epitaxy Growth of Oriented Nano-Array Structures on Perovskite Single Crystals.

Fabrication of organic-metal-halide perovskite micro-nano array structures draws attention to the potential application in polarized light, high-resolution X-ray imaging, light-emitting diodes, and lasers. However, it is still challenging to achieve the growth of controllable long-range ordered nanostructure arrays by chemical solution-based techniques. Herein, controllable epitaxial growth of long-range ordered micro-nano arrays on MAPbI3 single crystal (SC) surface is reported. A hydrated intermediate phase is found that can effectively regulate in-plane and out-plane orientated growth, respectively. This is attributed to the regulation of growth thermodynamics by hydration 0D perovskite intermediate phase enabling free recombination of PbI42- octahedral cages. Further, it is found that the degree of hydration is the key to the realization of in-plane and out-plane growth. Meanwhile, polarization emission and amplified spontaneous emission property are observed in highly oriented nanorod arrays with potential applications in anti-counterfeiting polarized emission.

Elimination of Interfacial-Electrochemical-Reaction-Induced Polarization in Perovskite Single Crystals for Ultrasensitive and Stable X-Ray Detector Arrays.

Organic-inorganic halide perovskites have exhibited bright prospects in high-sensitivity X-ray detection. However, they generally suffer from the severe field-driven polarization issue that remarkably deteriorates the detection performance. Here, it is demonstrated that the interfacial electrochemical reaction between Au electrodes and halogen in MAPbI3 single crystals (SCs) is the major source of the dark current polarization in the metal-semiconductor-metal (MSM)-structured perovskite X-ray detectors at the initial stage of biasing. By introducing the p- and n-type charge transport layers to isolate the electrodes from contacting the SC surface, the polarization is fully eliminated under a large electric field up to 1000 V cm-1 . Moreover, the resultant lateral p-i-n heterojunction suppresses the dark current of the devices by nearly 3 orders of magnitude as compared to the MSM counterparts and therefore enables a high sensitivity of 5.2 × 106  µC Gy-1 air cm-2 and a record low X-ray detection limit down to 0.1 nGyair s-1 . The excellent biasing stability and sensitivity of the devices allow to prepare the linear detector arrays for X-ray imaging applications.

Efficient and Stable Red Perovskite Light-Emitting Diodes with Operational Stability >300 h.

The long-term operational stability of perovskite light-emitting diodes (PeLEDs), especially red PeLEDs with only several hours typically, has always faced great challenges. Stable ß-CsPbI3 nanocrystals (NCs) are demonstrated for highly efficient and stable red-emitting PeLEDs through incorporation of poly(maleic anhydride-alt-1-octadecene) (PMA) in synthesizing the NCs. The PMA can chemically interact with PbI2 in the precursors via the coupling effect between O groups in PMA and Pb2+ to favor crystallization of stable ß-CsPbI3 NCs. Meanwhile, the cross-linked PMA significantly reduces the PbCs anti-site defect on the surface of the ß-CsPbI3 NCs. Benefiting from the improved crystal phase quality, the photoluminescence quantum yield for ß-CsPbI3 NCs films remarkably increases from 34% to 89%. The corresponding red-emitting PeLEDs achieves a high external quantum efficiency of 17.8% and superior operational stability with the lifetime, the time to half the initial electroluminescence intensity (T50 ) reaching 317 h at a constant current density of 30 mA cm-2 .

Electrospinning preparation and anti-infrared radiation performance of silica/titanium dioxide composite nanofiber membrane.

Silica/titanium dioxide (SiO2/TiO2) composite nanofiber membranes with different TiO2 content were prepared with the technology of electrospinning using ethyl orthosilicate, butyl titanate and polyvinyl pyrrolidone as silicon titanium sources and spinning aids. TGA, XRD, SEM and FT-IR were used to analyze the thermal decomposition process, phase composition, microscopic morphology and infrared properties of the products. The study showed that with the increase of the calcination temperature, the TiO2 phase gradually changed from amorphous to anatase structure. Above 900 °C, a sample containing rutile TiO2 with a higher refractive index was obtained. Simultaneously, the continuity of the sample deteriorated, and the mechanical properties deteriorated. The study found that after calcination at 900 °C, the fiber membrane with a TiO2 content of 12% had the lowest cost and the best overall performance, with tensile strength being 3.09 MPa, and thermal conductivity at 500 °C being 0.0899 W m-1 K-1, which is 20% lower than that of pure SiO2 fiber membrane. This research provides a reference for the development of high temperature insulation materials with good flexibility.

Electrospinning preparation and near-infrared absorption properties of a silica/cesium tungsten bronze micro-nano fiber membrane.

Silica/cesium tungsten bronze (SiO2/Cs x WO3) composite micro-nano fiber membranes were prepared by the co-precursor electrostatic spinning method using cesium chloride, tungsten powder and tetraethyl orthosilicate as raw materials. TGA, XRD, FT-IR, XPS, SEM and ultraviolet-visible-near red spectrophotometry were used to analyze the thermal decomposition process, phase composition, microscopic morphology and near-infrared absorption properties of the product. Studies have shown that as the ratio of Cs/W of raw materials increases, the crystallinity of Cs x WO3 in the product increases first and then decreases. When n(Cs)/n(W) reaches 0.5, its crystallinity is the most complete; similarly, calcination also contributes to the crystallization of Cs0.33WO3, but high temperatures above 800 °C will also destroy its crystal structure. The study found that after calcination at 700 °C, the fiber membrane with a Cs/W atomic ratio of 0.5 has the best infrared absorption performance. The average absorbance of near-infrared light at 780-2500 nm is 1.5, which is 5.56 times that of the pure SiO2 fiber membrane. The tensile strength reaches 2.4 MPa, which can meet practical requirements. This research provides a basis for the development of flexible solar shading materials under complex outdoor conditions.

Atomistic Surface Passivation of CH3NH3PbI3 Perovskite Single Crystals for Highly Sensitive Coplanar-Structure X-Ray Detectors.

Organic-inorganic halide perovskites (OIHPs) are recognized as the promising next-generation X-ray detection materials. However, the device performance is largely limited by the ion migration issue of OIHPs. Here, we reported a simple atomistic surface passivation strategy with methylammonium iodide (MAI) to remarkably increase the ion migration activation energy of CH3NH3PbI3 single crystals. The amount of MAI deposited on the crystal surface is finely regulated by a self-assemble process to effectively suppress the metallic lead defects, while not introducing extra mobile ions, which results in significantly improved dark current stability of the coplanar-structure devices under a large electric field of 100 V mm-1. The X-ray detectors hence exhibit a record-high sensitivity above 700,000 µC Gyair -1 cm-2 under continuum X-ray irradiation with energy up to 50 keV, which enables an ultralow X-ray detection limit down to 1.5 nGyair s-1. Our findings will allow for the dramatically reduced X-ray exposure of human bodies in medical imaging applications.

Dynamic Passivation in Perovskite Quantum Dots for Specific Ammonia Detection at Room Temperature.

Perovskite structured CsPbX3 (X = Cl, Br, or I) quantum dots (QDs) have attracted considerable interest in the past few years due to their excellent optoelectronic properties. Surface passivation is one of the main pathways to optimize the optoelectrical performance of perovskite QDs, in which the amino group plays an important role for the corresponding interaction between lead and halide. In this work, it is found that ammonia gas could dramatically increase photoluminescence of purified QDs and effectively passivate surface defects of perovskite QDs introduced during purification, which is a reversible process. This phenomenon makes perovskite QDs a kind of ideal candidate for detection of ammonia gas at room temperature. This QD film sensor displays specific recognition behavior toward ammonia gas due to its significant fluorescence enhancement, while depressed luminescence in case of other gases. The sensor, in turn-on mode, shows a wide detection range from 25 to 350 ppm with a limit of detection as low as 8.85 ppm. Meanwhile, a fast response time of ≈10 s is achieved, and the recovery time is ≈30 s. The fully reversible, high sensitivity and selectivity characteristics make CsPbBr3 QDs ideal active materials for room-temperature ammonia sensing.

Efficient lateral-structure perovskite single crystal solar cells with high operational stability.

The power conversion efficiency of perovskite polycrystalline thin film solar cells has rapidly increased in recent years, while the stability still lags behind due to its low thermal stability as well as the fast ion migration along the massive grain boundaries. Here, stable and efficient lateral-structure perovskite solar cells (PSCs) are achieved based on perovskite single crystals. By optimizing anode contact with a simple surface treatment, the open circuit voltage and fill factor dramatically increase and promote the efficiency of the devices exceeding 11% (0.05 to 1 Sun) compared to that of 5.9% (0.25 Sun) of the best lateral-structure single crystal PSCs previously reported. Devices show excellent operational stability and no degradation observed after 200 h continuous operation at maximum power point under 1 Sun illumination. Devices with scalable architectures are investigated by utilizing interdigital electrodes, which show huge potential to realize low cost and highly efficient perovskite photovoltaic devices.

Combined use of radiocarbon and stable carbon isotope to constrain the sources and cycling of particulate organic carbon in a large freshwater lake, China.

The concentrations and isotopic compositions of dissolved inorganic carbon (DIC) and particulate organic carbon (POC) were measured in order to better constrain the sources and cycling of POC in Lake Fuxian, the largest deep freshwater lake in China. Model results based on the combined δ13C and Δ14C, showed that the average lake-wide contributions of autochthonous POC, terrestrial POC, and resuspended sediment POC to the bulk POC in Lake Fuxian were 61%, 22%, and 17%, respectively. This indicated autochthonous POC might play a dominant role in sustaining large oligotrophic lake ecosystem. A mean 17% contribution of resuspended sediment POC to the bulk POC implied that sediment might have more significant influence on aquatic environment and ecosystem than previously recognized in large deep lakes. The contributions of different sources POC to the water-column POC were a function of the initial composition of the source materials, photosynthesis, physical regime of the lake, sediment resuspension, respiration and degradation of organic matter, and were affected indirectly by environmental factors such as light, temperature, DO, wind speed, turbidity, and nutrient concentration. This study is not only the first systematic investigation on the radiocarbon and stable isotope compositions of POC in large deep freshwater lake in China, but also one of the most extensive radiocarbon studies on the ecosystem of any great lakes in the world. The unique data constrain relative influences of autochthonous POC, terrestrial POC, and resuspended sediment POC, and deepen the understanding of the POC cycling in large freshwater lakes. This study is far from comprehensive, but it serves to highlight the potential of combined radiocarbon and stable carbon isotope for constraining the sources and cycling of POC in large lake system. More radiocarbon investigations on the water-column POC and the aquatic food webs are necessary to illuminate further the fate of autochthonous POC, terrestrial POC, and resuspended sediment POC, and their eco-environmental effects.