Blue nanocrystal perovskite LEDs have traditionally lagged behind their red and green cousins. Here, we discuss the reasons for this lag and propose solutions to these problems, producing high efficiency blue perovskite LEDs. We demonstrate the NiOx, a transport material in one of the highest performing devices to date, reduces the performance of nanocrystals near to the interface. By replacing it with an alternative transport structure, we show that the nanocrystal emission is unperturbed. We then build full LEDs out of this transport structure, increasing the EQE from 0.03% to 0.50%, the highest for inorganic perovskite nanocrystals at this wavelength. We further show that the benefits of this transport structure relax as the energetics redshift, as our blue-green devices match those from literature. These results are a useful step forward towards commercially relevant perovskite LEDs.
Organic-inorganic perovskites have revolutionized the optoelectronics field, providing materials with a wide range of properties for solving numerous applications. Indeed, much recent work has been focused on nanostructured perovskites, with quantum dots, nanowires, and nanoplatelets showing tremendous potential. Here, we utilize the unique tunability of 2D perovskite nanoplatelets to build LEDs that span the visible spectrum. Quantum confinement in the z direction drives a significant blueshift, allowing for blue devices utilizing the bromide system and orange devices utilizing the iodide system. We demonstrate that excess ligand addition is crucial to achieving this blueshift in thin films that otherwise suffer from energy funneling. We build devices that show electroluminescence from 440 nm to 650 nm, although they still suffer from low efficiencies due to low photoluminescence quantum yields. We finally demonstrate that these materials suffer from reversible degradation with an applied electric field, further limiting the efficiency. The favorable optoelectronic properties of perovskite materials, combined with the blueshift due to quantum confinement, shows the promise of these materials as a new class of low cost emitters.
Conference Committee Involvement (1)
Physical Chemistry of Semiconductor Materials and Interfaces XVIII
11 August 2019 | San Diego, California, United States