Halide Perovskite Light-emitting Devices: Ionic Doping and Nanostructuring in Single Layer LEC and Laser

Abstract

Metal halide perovskites, as a new type of hybrid semiconductors, have demonstrated promising optoelectronic properties for state-of-the-art and emerging photonic technologies such as pure color light-emitting diodes, cost-effective nano-lasers, and efficient photovoltaic devices. Owing to highly tunable emission wavelengths, high absorption coefficient, high exciton binding energy, narrow emission linewidth, and less expensive fabrication methods, perovskite materials are excellent choices for the next generation of optoelectronic applications. In this dissertation, we mainly focus on introducing and understanding the physics and processing of the perovskite lightemitting devices regarding their dynamic behavior associated with ionic doping and nanopatterning effects in perovskite materials. We begin by investigating a novel and facile approach to overcome some important limitations of Perovskite Light-Emitting Electrochemical Cells (PeLECs) such as intrinsic ion motion degradation, low brightness, and short operational lifetime. In this method, we leverage the advantages of new nanocomposite with an electrolyte polymer along with a lithium salt additive (LiPF6) incorporated into the CsPbBr3 perovskite structure in order to passivate and suppress the traps, defects, and pin-holes in perovskite thin films aiming to improve the morphology and achieve high-performance single layer PeLEC for green emission. By implementing the material characterization techniques, we scrutinize the optimization process for lithium salt additive and demonstrate the advantages of LiPF6 additive including high photoluminescence quantum yield (PLQY), and stable photoluminescence (PL) dynamics, electroluminescence (EL) stability, low hysteresis, and high efficiency of devices. Inspired by the successes of ionic additives in these types of PeLECs, we further investigate the operational stability of devices and reach 100 hours of operational lifetime which is a 5.6-fold improvement over devices with no LiPF6 additive. We further develop our research by utilizing a new synthesized ionic iridium complex to build a HostGuest system in PeLEC structure in order to effectively tune the color emission, improve the morphology and consequently increase the efficiency of PeLECs for future display applications. In the next part of this dissertation, we provide a unique method to construct a multilayer blue Perovskite Light-Emitting Diode (PeLED) by utilizing the electron and hole transport layers as well as Quasi-2D perovskite composition. We successfully show that implementing two long and small ligands into the 3D perovskite precursor can beneficially form both small and large n phases perovskite layers, for the selective energy transfer process, and eventually provide an extremely efficient blue PeLED device. The maximum 10% EQE, maximum luminance 5500 cd m-2 , and 170 min half lifetime (T50) operational stability have been demonstrated. In the last section, we present the novel nanoimprint lithography method in order to perform direct nanopatterning on halide perovskite thin films to create laser cavities. With a meticulous approach that includes a practical encapsulation method, we have exhibited the first demonstration of quasi-CW lasing from directly patterned perovskites with a high-quality cavity design.