Development of High Performance Organic-Inorganic Halide Perovskite Optoelectronic Devices via Morphological and Interfacial Manipulation
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Organic-inorganic halide perovskites (OIHPs) have emerged as excellent solution processable semiconductors for a new generation of potentially printable and efficient optoelectronic devices in recent years, including photodetection, energy harvesting, and light-emitting devices. The rise to prominence for this class of materials is fueled by their superior properties, such as tunable bandgap, high carrier mobility, outstanding optoelectronic merits, and low-cost solution processability. Given all exciting properties, solution-processed perovskite thin film also shows very challenging characteristics including difficult morphology control and substantial defects at film surface and grain boundaries (GBs). In this dissertation, integrated morphological and interfacial approaches have been utilized to overcome the above-mentioned challenges and further enhance performance of OIHP optoelectronic devices. Chapter 1 briefly overviews basics of perovskite material, current status of various perovskite optoelectronic devices, and remaining challenges for obtaining high quality solution processed perovskite thin film. Chapter 2 introduces common experimental details involved in this work including material preparation, material property characterization, device fabrication and performance test. Chapter 3 demonstrates a fast (<1s) and simple post deposition chemical treatment during which crystal reconstruction induced by a methylamine (MA0) vapor greatly improves perovskite film coverage, crystallinity, and perovskite solar cell (PSC) performance. In Chapter 4, another method to improve perovskite film morphology is proposed. An ion exchange method for conversion from two-dimensional (2D) to three-dimensional (3D) perovskite is developed to grow highly oriented methylammonium lead bromide (MAPbBr3) thin films with much-improved substrate coverage. The enhanced film quality leads to ultra-narrow electroluminescence spectra (15.3 nm full width half maximum (FWHM) and 98.10% color purity) and demonstrates immense potential of the ion exchange method for achieving ultrahigh resolution displays. Chapter 5 presents a simple defect passivation method by post-treating CH3NH3PbI3 (MAPbI3) film with diammonium iodide NH3I(CH2)8NH3I (C8). Bilateral ammonium iodide end of C8 can simultaneously passivate perovskite layer and dope adjacent electron-transporting layer in derived PSCs. Consequently, the thin-film PSC passivated by C8 show reduced recombination loss and a much-improved power conversion efficiency (PCE) of 17.2% compared to 14.7% of the control device.