LEDs from Metal Halide Perovskites

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