David Mitzi1
Duke University1
Recent literature provides a stream of new recipes and processing techniques for halide perovskite semiconductors, leading to improved optoelectronic device performance and power conversion efficiencies for photovoltaics (PVs), although often with limited detailed understanding of the underlying mechanisms. For example, additive engineering and stoichiometric variations are particularly interesting in terms of controlling defects and optimizing performance levels within solar cells and related devices. However, the underlying impact of additives and stoichiometry on film grain structure, transport, and defect properties is often not well understood. This talk will address recent efforts to examine shoichiometry control and additive engineering in the model system CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub>, using a variety of tools, including a new carrier-resolved photo-Hall (CRPH) technique [1,2] and <i>in-situ</i> X-ray and photoluminescence characterization during film deposition [3,4]. In particular, the CRPH approach [1] provides unique insights into the majority <i>and</i> minority carrier properties, as a function of light intensity and using the same sample and measurement. The talk will also involve another important aspect of additive and defect engineering, namely doping (Fermi level) control [5]. A recent demonstration [6] shows that careful selection of molecular dopant and perovskite band positions enables five orders of magnitude control over conductivity and carrier density in a mixed-metal CH<sub>3</sub>NH<sub>3</sub>Sn<sub>0.5</sub>Pb<sub>0.5</sub>I<sub>3</sub> perovskite. Such fundamental studies related to grain structure, defect properties and doping are expected to provide an enhanced degree of control over semiconducting properties for PV and related optoelectronic devices.<br/><br/><b>References:</b><br/>[1] Gunawan, O.; Pae, S. R.; Bishop, D. M.; Virgus, Y.; Noh, J. H.; Jeon, N. J.; Lee, Y. S.; Shao, X.; Todorov, T.; Mitzi, D. B.; Shin, B. Carrier-Resolved Photo-Hall Effect. <i>Nature </i>2019, 575, 151-155.<br/>[2] Euvrard, J.; Gunawan, O.; Mitzi, D. B. Impact of PbI<sub>2</sub> Passivation and Grain Size Engineering in CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> Solar Absorbers as Revealed by Carrier-Resolved Photo-Hall Technique. <i>Adv. Energy Mater.</i> 2019, 9, 1902706.<br/>[3] Abdelsamie, M.; Li, T.; Babbe, F.; Xu, J.; Han, Q.; Blum, V.; Sutter-Fella, C. M.; Mitzi, D. B.; Toney M. F. Mechanism of Additive-Assisted Room-Temperature Processing of Metal Halide Perovskite Thin Films. <i>ACS Appl. Mater. Interfaces</i> 2021, 13, 13212-13225.<br/>[4] Han, Q.; Bai, Y.; Liu, J.; Du, K.-z.; Li, T.; Ji, D.; Zhou, Y.; Cao, C.; Shin, D.; Ding, J.; Franklin, A. D.; Glass, J. T.; Hu, J.; Therien, M. J.; Mitzi, D. B. Additive Engineering for High-Performance Room-Temperature-Processed Perovskite Absorbers with Micron-Size Grains and Microsecond-Range Carrier Lifetimes. <i>Energy Env. Sci. </i>2017, 10, 2365-2371.<br/>[5] Euvrard, J.; Yan, Y.; Mitzi, D. B. Electrical Doping in Halide Perovskites. <i>Nature Rev. Mater. </i>6, 531-549.<br/>[6] Euvrard, J.; Gunawan, O.; Zhong, X.; Harvey, S. P.; Kahn, A.; Mitzi, D. B. p-Type Molecular Doping by Charge Transfer in Halide Perovskite. <i>Mater. Adv. </i>2021, 2, 2956-2965.