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.
