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Metal halide perovskites have emerged as a new class of low-cost solution processable semiconductor materials with applications in a variety of optoelectronic devices, from photovoltaics, to photodetectors, lasers, and light emitting diodes (LEDs). Efficient electrically driven LEDs with green light emission based on lead bromide perovskites, such as MAPbBr3 and CsPbBr3 have been achieved. While electrically driven perovskite LEDs have shown great promise with the device efficiency approaching to those of organic and quantum dot LEDs, a number of challenges, such as long-term stability and color tunability, remain to be addressed before the consideration of commercialization. For full-color display and solid-state lighting applications, highly efficient blue and red LEDs are required in addition to green ones, which however have yet achieved comparable device performance for perovskites-based devices. To implement red perovskite LEDs, two major strategies have been attempted to date, one relying on mixing halide, and the other involving the control of quantum well structures. Mixing halide has been shown to enable precise color tuning of photoluminescence and electroluminescence of perovskite LEDs. However, mixed halide perovskites show relatively low photoluminescence quantum efficiency. More critically, mixed-halide perovskites suffer from low spectral stability due to ion migration and phase separation under illumination and electric field. the change of electroluminescence color during the device operation has been observed in all LEDs based on mixed-halide perovskites. In this invention disclosure, we report bright and efficient red perovskites LEDs with great spectral stability by using quasi-2D halide perovskites/polymer (i.e. PEO, PVK, PIP, etc.) composite thin films as the light-emitting layer. By controlling the molar ratios of large organic salt (i.e. benzyl ammonium iodide, phenethylammonium iodide, butylammonium iodie, etc.) and inorganic salts (Csl and Pbl2), FSU researchers have been able to obtain luminescent quasi-2D perovskite thin films with tunable colors from red peaked at 615 nm to deep red peaked at 676 nm. The perovskites/polymer composite approach enables quasi-2D perovskite/PEO composite thin films to possess much higher photoluminescence quantum efficiencies and smoothness than their neat quasi-2D perovskite counterparts. Advantages include: 1. These quasi-2D halide perovskites/polymer composite thin films have high photoluminescence quantum efficiency and superior thin film morpology. 2. Electrically driven LEDs with tunable emissions based on quasi-2D halide perovskites/polymer composite thin films have been achieved with superior device performance. 3. These devices show exceptional EL spectra stability and device performance stability.
Key Words : Chemical Synthesis, LEDs, Perovskites
Low-cost, nontoxic, highly stable industrial organic pigments are utilized as surface passivation agents for perovskite solar cells (PSCs).
Next-generation thin-film perovskite solar cells have been shown to have major advantages over their silicon-based counterparts. They are low-cost, highly efficient, and are simple to synthesize from earth-abundant materials. However, to become truly competitive with current on-the-market solar cells, PSCs need to overcome the challenge of long-term stability while maintaining their ability to be mass-produced.
Dr. Biwu Ma of Florida State University has developed a method to apply a layer of organic pigments to PSCs as a passivation agent, increasing the useable lifespan of these solar cells. The pigments are well-known, low-cost, and have been shown to improve the efficiency PSCs; in one experiment, the efficiency of a solar cell was increased from 18.9% to 21.1% with the application of the pigment.
The pigments are applied via solution processing of soluble pigment derivatives followed by thermal annealing to convert them into insoluble coating. This enables effective passivation through strong interactions organic pigments and the metal halides of the solar cell. Together with the hydrophobicity of the coating, this enables highly efficient PSCs with remarkable stability.
Dr. Ma has recently developed highly efficient X-ray scintillators with state-of-the-art performance based on organic metal halide hybrids, which could be prepared using a facile solution growth method at room temperature to form inch-sized single crystals. These organic-inorganic hybrid materials with a zero-dimensional
(0D) structure at the molecular level exhibit tunable emissions in the visible spectrum region with high photoluminescence quantum efficiencies (PLQEs) of up to 100%. X-ray imaging tests have showed that scintillators based on powders could provide an excellent visualization tool for X-ray radiography, and
flexible scintillators could be fabricated by blending powders with polymer matrix, such as polydimethylsiloxane (PDMS).
These X-ray scintillators have numerous advantages over currently-used materials: