Towards High-Efficiency and High-Brightness Perovskite Quantum Dot Light-Emitting Diodes

Abstract

Metal-halide perovskite quantum dots show immense promise for future display and single-photonemission applications owing to their unique properties for optoelectronics applications, including their high defect tolerance, high photoluminescence quantum yields, facile processibility, and ease of spectral tunability. My work focuses on the integration of such perovskite quantum dots into quantum dot light-emitting diodes (QLEDs), including optimizing strategies for achieving higher brightness with an attention to interlayer, architecture, and ligand design. As rapid and exciting developments continue to unfold in the field of photovoltaics, there is an increasing need to translate the developments and lessons from the photovoltaics space into making more efficient, bright, and stable light-emitting diodes. In this work, I develop a deeper understanding of how interfacial modifiers of great relevance in photovoltaics can also lead to exciting performance gains in QLEDs. The use of a phosphonic acid hole-injecting interface material allows us modify the work function of the indium tin oxide (ITO) interface, thereby allowing us to achieve device brightnesses far exceeding what had previously been demonstrated for perovskite QLEDs, enabling brightness levels that were previously only attainable by 3-dimensional perovskite emitters. We explore the mechanisms underlying the superior brightness that can be achieved in QLEDs with the use of such interfacial modifiers. My second major advancement in the field involves the use of the carbazole phosphonic acid species as a ligand candidate binding to surface sites of the quantum dots in the active layer. The use of the species both as a ligand candidate and as an interfacial modifier enables us to achieve surface passivation and energy level modification directly in the quantum dot layer to enable improved charge injection balance throughout the device. Finally, I develop a Bayesian toolkit for the efficient characterization of single photon emitters (SPE) for rapid and robust screening of SPE’s for single photon purity and character. I explore Lasso regularization and Bayesian noise reduction techniques and contrast the Bayesian approach to least squares (?2) or maximum log likelihood estimation for predicting g2(0) values. This is accompanied by a single photon emitter simulator, enabling the user to generate simulated g2(?) traces to match observed experimental emitter behavior and noise levels, while also running statistical confidence interval tests on the estimation protocols. This tool contributes to the streamlining of experimental workflows in assessing the single photon character of single photon emitters such as quantum dots and defects in diamond in a high-throughput fashion, or when the data may be signal-to-noise limited.