Research On Optimization Of Perovskite Films In Organic-inorganic Hybrid Perovskite Light-emitting Devices

As a kind of solid-state display devices, light-emitting devices(LED) have attracted considerable attention for decades because of high display quality, wide working temperature range, low power consumption, thin-type and light mass, etc. Since 21 th century, growing with the application demand of lighting and display, improving the properties of LED has been the key for satisfying its application in the future. Research and development of new materials has become the research emphasis of improving the display quality of LED.To date, there are many excellent light-emitting materials that have been researched and developed. The light-emitting materials mainly include inorganic light-emitting materials(II-VI semiconductor doped rare earth element or transition elements), organic materials(small molecules and polymers) and organic–inorganic hybrid light-emitting materials(Organic–inorganic hybrid perovskite or quantum dots). Perovskite materials possess both the remarkable qualities of inorganic semiconductor(high charge-carrier mobility) and the facile processability of organic semiconductors(easy solution processing) as it is comprised of inorganic semiconductor and organic semiconductor in molecular level. Meanwhile, organic–inorganic hybrid light-emitting materials can tune the property itself through designing and tailoring the material in the combination process. Through substituting the bromide(Br-) ion with chloride(Cl-) or iodide(I-) ions, the bandgap of perovskite materials can be changed and the tuning over the entire visible spectral range(390nm~790nm) can be achieved. A narrow PL spectral width and high PL quantum yield indicate that perovskite materials have strong PL properties, making them potential candidates for use in light-emitting devices. But perovskite materials have poor film-forming properties which limit its application in light-emitting devices.In this paper, we successfully fabricate large crystallite, high crystallinity CH3NH3 Pb Br3 perovskite film and improve the surface coverage of perovskite film through optimizing crystallization in the spin-coating process. Due to this formation technique for CH3NH3 Pb Br3 perovskite thin-films, we were able to improve the electroluminescence(EL) properties of perovskite light-emitting device. The improved perovskite crystallites can be achieved by depositing a DMF solvent layer before single-step spin-coating which can provide a long time of wet environment under the concentration of CH3NH3 Pb Br3 solution unchanged to promote the grain growth. From the SEM images we can see CH3NH3 Pb Br3 films produced by our formation technique efficiently improve the grain size and surface coverage of perovskite film. Intense XRD signal of films produced by our formation technique can be observed from the XRD graph. As the quality of perovskite film is increased, we observed an associated increase in the lifetime(from 1.05 ns to 2.50 nm) and the full width at half maximum(FWHM) of PL spectra is only 31 nm. The CH3NH3 Pb Br3 perovskite LED without pre-depositing a DMF layer exhibited a maximum luminance of 340.6 cd/m2 and an external quantum efficiency(EQE) of 0.405%. By contrast, the CH3NH3 Pb Br3 perovskite LED with, in which the quality of perovskite film was improved, exhibit a remarkably improved maximum luminance of 2088 cd/m2 and an EQE of 0.728%. The electroluminescence from the representative device is uniform and the FWHM of the emission was only 20 nm. The perovskite film produced by our formation technique can improve the stability of device.