Research Terms
Industrial Engineering Manufacturing Engineering
Keywords
Famu-Fsu College Of Engineering
Industries
Industrial Engineering Manufacturing Engineering
In recent years, remarkable optoelectronic properties have been discovered in a group of halide perovskite semiconductors. Their potential to invigorate the current solar cell and light-emitting diode (LED) industries has been demonstrated by achieving very high device efficiencies in relatively short periods. While higher efficiency records are pursued, an equally important task is to improve their device reliability. So far, most reported perovskite solar cells and LEDs employed a polycrystalline thin film for light absorbing or light emitting purposes. The size of the grains in such films typically varied from sub-100 nanometers to a few micrometers. The high density of grain boundary defects can trap charge carriers and aid the diffusion of water molecules and ionic species in the perovskites, deteriorating their structural integrity and transportation properties in long-term applications.
We recently have invented a new process enabling the formation of perovskite thin films with a ultra-large and uniform grain size. The large grain size will significantly reduce the density of grain boundaries, and the films perform nearly the same as single crystalline materials. In addition, the simple solution process in our approach will potentially more practical to scaled up for future high throughput industrial production. The new discovery is based on our scientific understanding to precisely control the nucleation sites and nucleation densities of halide perovskites during film formation on a substrate.
Our halide perovskite thin films with large and uniform grains can exhibit enhanced structural and morphological stability in ambient air. For instance, efficient LEDs had been made with our methylammonium lead tribromide films after exposing them in air for three months without encapsulation. Our halide perovskite thin films also showed greatly reduced ionic migration tendency under an external electrical field. Photo-detectors had been fabricated using our methylammonium lead triiodide films. The devices exhibited 10 times lower dark current at a constant applied voltage compared to devices with conventional halide perovskite thin films that were processed using previously reported methods. In addition, no measurement hysteresis was observed in our halide perovskite thin films when a dynamic voltage was applied at both dark and illuminated conditions.
An FSU researcher created a novel material comprised of halide perovskite crystals embedded in a polymer matrix for radiation blocking and detection. The material is lightweight and lead free. Other materials require expensive and long manufacturing processes, but this novel material can be manufactured in a variety of ways such as solution-based drop casting, hot pressing, melt extrusion, injection molding, and 3D printing, to save time and money. Electrodes can be embedded in the material for passive and accurate x-ray and gamma-ray detection.
Third party independent testing has shown that the material is 50% more effective than current state of the art radiation blocking technology. These semiconducting nanocrystals are uniformly dispersed in the polymer matrix to not only block radiation but also detect high energy radiation.
Organometal halide perovskite (Pero) materials have been recently intensively explored. They are ideal in forming optoelectronic devices due to their optical and electronic properties. For example, solar cells with a thin layer of methyl ammonium lead iodide have achieved about 20% power conversion efficiency, approaching the state-of-the-art performance of polycrystalline thin film solar cells. Pero materials also exhibit high photoluminescence yield and can be tuned to cover the visible spectrum, thus they are potentially valuable in light-emitting diodes (LEDs) for information displays and lighting luminaires.
We have created single-layer LEDs using a composite thin film of Pero and poly(ethylene oxide) (PEO). In contrast to the multi-layer strategy, a simplified device structure is certainly advantageous in terms of processing flexibility and fabrication cost at the manufacturing stage. Our single-layer thin films are synthesized by a one-step spin coating process and have a device structure that resembles “bottom electrode (ITO)/Pero-PEO/top electrode (In/Ga or Au)”. In spite of the simple device structure, the green emission LEDs with methylammonium lead bromide (bromide-Pero) and PEO composite thin films exhibit a low turn-on voltage of ~2.8-3.1V (defined at 1 cd m-2 luminance), a maximum luminance of 4064 cd m-2 and a moderate maximum current efficiency of ~0.24-0.74 cd A-1. Such performance is on par with reported results in literature involving a more complex multi-layer device structure. Blue and red emissions LEDs have also been fabricated.
Organometal halide perovskites (Pero) have been well known for their astounding opto-electronic properties and in their utilizations in photovoltaic cells and light emitting diodes (LEDs). They are highly efficient, have low processing temperatures, and are cost effective. For Pero solar cells, the highest power conversion efficiency has reached about 20%, which approaches the best efficiencies of thin film solar cells. With continuing efforts to improve device efficiency and operational stability, the next challenge is to develop Pero solar cells and LEDs using a scalable printing technique to fulfill the promise of large scale, low cost devices.
The present technology is first to develop printed Pero LEDs on rigid indium tin oxide (ITO)/glass and flexible carbon nanotubes (CNTs)/polymer substrates. The devices have ITO or CNTs as the transparent anode, a printed composite film consisting of methyl ammonium lead tri-bromide (Br-Pero) and polyethylene oxide (PEO) as the emissive layer, and printed silver nanowires as the cathode. The printing process can be carried out in air without any deliberate control of humidity; in fact, printing the PEO/Br-Pero in air actually improves its photoluminescence properties. The light intensity, turn-on voltage, and maximum luminescence compare favorably to existing Pero LEDs that are made of multi-layer structures which are formed by more complex fabrication techniques.
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Halide perovskites have emerged as a new generation semiconducting materials for LED applications. A recent finding at the Flroida State University found by adding an ionic insulating polymer into the mixture of perovskite/ionic-conducting polymer the device can perform significantly better. The use of a ternary composite to replace the previously used binary composite can help optimize the morphology and crystallinity of the perovskite materials, which led to efficient charge injection and transportation in the composites.
This invention allows LEDs to achieve a reach of 800,000 cd m-2, 40x higher than the previous record. These devices can also be switched on at 1.8V, 40 percent lower than the devices with a binary composite.
Commercial neutron detectors have problems of heavy weight, high power consumption and low response speed. This new invention disclosed a new method of manufacturing compact boron nitride-phosphor composites for efficient, portable, and fast-responding thermal neutron detection. Since the composite can be manufactured like conventional commodity plastics using a solution or compress molding process, they can be made at a very-low cost and large area, enabling a high efficiency of stand-off detection and imaging of thermal neutrons in presence of special nuclear materials and nuclear events.
Advantages
Numerous materials have been used for radiation protection. For example, radiation protection materials have been used in articles of clothing, such as gloves, but such materials typically include relatively low concentration of particles, such as concentrations of up to 80 %, by weight, of embedded particles. Greater concentrations have not been used, because doing so makes it difficult, if not impossible, to maintain suitable flexibility of the materials. There remains a need for flexible radiation shielding composite materials with high attenuation, including materials that can maintain a desired degree of flexibility at relatively high particle concentrations.
This invention embodies composite materials including bismuth oxide that may be flexible and include relatively high particle loadings. These composite materials, therefore, may be flexible, and have very high attenuation properties per unit thickness and/or per unit weight. The potential uses are improved flexible and stretchable radiation protection material which have potential uses in clothing, gloves, and more.
Advantages
Ceramics and their composites are demanded for high temperature and extreme environment applications. However, they are brittle and easy to crack especially upon mechanical shock and thermal shock. We discovered that by incorporating nanotube/nanowire fillers and following the manufacturing procedure in this invention, high performance ceramic composites can be obtained with greatly enhanced mechanical shock resistance and thermal shock resistance. The composite can also be rapidly fabricated with 10-50 times improvement of manufacturing throughput.
Advantages:
