Metal halide perovskites for light-emitting applications

Resumen

In the past decade, flat-panel displays have become ubiquitous due to the proliferation of modern electronic devices such as laptops, tablets, and smartphones. This has steered scientific efforts towards innovating electroluminescent materials that are energy efficient and possess excellent emission properties. As a result of extensive research, evaporated organic light emitting diodes emerged as a successful display technology and have since enjoyed significant market penetration. However, they have broad emission spectra and are also fairly expensive particularly for flexible displays. Thus, low-cost solution-processed light-emitting materials that exhibit colour pure electroluminescence are invaluable for next-generation display and lighting technologies. In this dissertation, novel light-emitting diodes based on perovskite semiconductors are presented. Some of their beneficial properties include bandgap tunability, balanced charge carrier mobilities, colour-pure emission with a full-width at half maximum of < 20 nm, solution processability, and low material cost. These attributes make them particularly attractive for low-cost light-emitting applications. By developing a device with suitable charge transport layers and by optimizing the perovskite deposition protocol, perovskite light-emitting diodes (PeLEDs) with luminance exceeding 17,000 cd/m2 with an external quantum efficiency of 3.9% were obtained. Further analysis shows that the key to better performance lies in fabricating thin and dense perovskite layers composed of tiny crystallites. Additionally, a novel gas-assisted perovskite thin-film deposition protocol was developed which is compatible with commercial roll-to-roll manufacturing techniques. Using this technique, large area devices with uniform emission were fabricated on a 230 cm2 substrate. While the efficiencies of PeLEDs have been gradually growing in the past four years, their operational lifetime needs to be addressed as it is relatively short. Here, the underlying degradation mechanisms in PeLEDs that limit their lifetime are elucidated. Decomposition of the organic cations in the perovskite layer seems to be the major degradation factor under bias. By replacing the organic cation with an inorganic cation their operational lifetime can be substantially improves. The insights provided in this dissertation are likely to catapult emerging PeLED technology further.