Engineering research seminar with Nakita Noel, Associate Research Scholar, Princeton University, presenting a variety of defect mitigation strategies for perovskite-based devices.
Meeting ID: 966 5391 3134
Within the past decade, metal halide perovskites have been attracting significant interest due to their versatile use in a wide range of applications. These materials have been used in lasers, photodetectors, and most commonly, in photovoltaic devices and light emitting diodes. Despite the cheap and simple fabrication methods by which these materials are deposited, the resulting perovskite films are effectively high-quality semiconductors, and the power conversion efficiencies of lead halide perovskite solar cells are now exceeding certified values of 25%. However, perovskite-based devices are yet to achieve their full potential. One of the major hindrances to achieving this, is an incomplete understanding of defects at perovskite surfaces and interfaces. Deficiencies at these interfaces may be responsible for the largest losses in perovskite-based optoelectronic devices; limiting charge extraction, increasing non-radiative recombination rates and leading to hysteresis, and significantly increasing the voltage loss in perovskite photovoltaics.
Herein, I will present a variety of defect mitigation strategies, from manipulating solution chemistry to interface modification strategies. Importantly, I will focus on the utilisation of charge-transfer dopants to dope the perovskite interface, resulting in the formation of narrow homojunctions. These homojunctions result in reduced interfacial recombination, suppressed hysteresis and improved device performance, yielding steady-state device efficiencies of over 21%. I will also discuss the use of ionic liquids at the metal-oxide perovskite interface and show that not only do they affect the work function of the metal oxide, but also interact strongly with the perovskite causing a shift in the Fermi level of the material such that it moves toward the conduction band. A variety of optoelectronic measurements show that this approach significantly improves the quality of the perovskite film through reducing the trap density by an order of magnitude. The utility of these defect mitigation strategies extends beyond perovskite solar cells and can also be used to further improve the performance other perovskite optoelectronic devices, bringing this promising technology closer to commercialisation.
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