Light-emitting diode (LED) refers to a light source which has a longer lifetime, emit less heating, and use less electricity consumption as compared to both incandescent bulb and other light sources. When red, green, and blue LED all combine then they produce a white light source, which function as an alternative energy-saving white light source which we all are using in our daily life e.g. mobile backlight, home light, car headlights, and mobile and TV display. However, the existing commercial LED technologies typically rely on high temperature and high vacuum manufacturing processes which increase the fabrication and equipment costs. Therefore, a new class of materials-metal halide perovskite-have been shown great potential for green and red LEDs which can be cheaper for lighting and displays technology. But the poor device efficiency and colour stability i.e. during device operation, the emission colour of the blue LED shifts in the green spectral region which leads to poor device performance.
The project has partially achieved its objectives and milestones for the period. This project includes three objectives, from materials to films and device fabrication, which are shown as follows-
• To synthesize novel quasi-2D perovskites for blue electroluminescence (EL) with excellent optoelectronic properties. We have designed and synthesized a series of efficient and stable quasi-2D perovskite emitters by optimizing the organic spacer cations and employing mixing of the short ligand group to stabilize the colour stability. The work is under investigation for the design of quasi-2D perovskite through short chain ligand to enhance the colour stability and device performance. Moreover, we have found that the use of a small amount of organic diammonium halide group can lead to the formation of colour-stable perovskite for blue emission. Based on such new materials, we have developed blue PeLEDs with excellent colour stability and reasonable device performance.
• To deposit high-quality quasi-2D perovskite films. We have obtained a series of high-quality quasi-2D perovskite films by controlling the ratio of long chain and short chain ligand and surface defects passivation with metal doping. We also used the anti-solvent method to get high-quality perovskite films. However, the anti-solvent treatment does not help to maintain the peak position of the blue emission. To resolve this, we used a co-solvent approach to deposit high-quality perovskite thin film, and the overall emission properties are improved.
• To fabricate efficient and stable blue PeLEDs beyond the state-of-the-art. We have fabricated a number of efficient and colour-stable blue PeLEDs based on p-i-n device architectures. We have also achieved blue PeLEDs with 7.7% EQE and 1484 cd/m2. Furthermore, we have carried out device physics studies on blue emissive PeLEDs and found that the EL emission peak does not shift with the voltage scan.
