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.

About the Speaker(s)

Nakita Noel
Associate Research Scholar, Princeton University

Dr. Nakita K. Noel obtained her undergraduate degrees in chemistry and physics at the University of the West Indies, St. Augustine. After this she joined the laboratory of Prof. Henry J. Snaith at the University of Oxford where she undertook her PhD in condensed matter physics. During her PhD, Dr. Noel focused on tailoring the composition and surface chemistry of metal halide perovskites with the goals of reducing toxicity and improving the efficiency of perovskite-based photovoltaics. After completing her PhD, she stayed on at Oxford as a postdoctoral researcher where her main focus was understanding the fundamental chemistry of the perovskite precursor solutions and its impact on the crystallisation on perovskite films. Based on the insights gained from this work, she developed a new low-boiling point solvent for the deposition of perovskite thin films and linked a fundamental solvent decomposition process to the dissolution of colloids in perovskite precursor solutions, providing a simple route to fabricating perovskite solar cells with record low voltage losses. Noel then moved to Princeton University to take up a Materials Science Postdoctoral Research Fellowship in the Princeton Center for Complex Materials working primarily with Prof. Craig B. Arnold. Here, she studies the detailed chemical composition of perovskite precursor inks and its impact on crystallisation kinetics, and the role of interfaces and defects on the performance of perovskite optoelectronics.

Contact

For more information, contact Ashley Parker at ashley.l.parker@dartmouth.edu.