Abstract:

With the advancement of technology, there is an increasing demand for multifunctional materials that combine optical, electronic, mechanical, and ionic properties. Hybrid metal halide semiconductors (MHS) have emerged as promising candidates for a wide range of optoelectronic applications, including solar cells, light-emitting diodes (LEDs), photodetectors, and lasers. These materials exhibit a unique set of finely tunable properties, providing a versatile platform for addressing limitations in currently available technologies. In particular, introducing controlled porosity could enable their use in previously unexplored applications such as sensing, electrocatalysis, and solid-state batteries, while the assembly of crystalline MHS that integrate the characteristics of both organic and inorganic semiconductors can open new directions in materials engineering.

Motivated by these synthetic challenges, we recently developed a general strategy for generating porosity in MHS using molecular cages serving as structure-directing agents and counter-cations. [1-3] The reaction of the [2.2.2] cryptand (DHS) linker with Pb(II) in acidic media gave rise to the first porous 2D metal halide semiconductor with formula (DHS)2Pb5Br14. The corresponding material is stable in water for over three years, while gas and vapor sorption studies revealed that it can selectively and reversibly adsorb H2O and D2O at room temperature (RT). Solid-state NMR measurements and DFT calculations verified the incorporation of H2O and D2O in the organic linker cavities, and shed light on their molecular configuration. The recorded water stability is unparalleled for hybrid metal halide and perovskite materials, while the generation of porosity opens up new pathways toward unexplored applications (e.g., solid-state batteries and the hydrogen evolution reaction (HER)) for this class of hybrid semiconductors.

Taking a step further in material design, we implemented molecular and crystal engineering to design and synthesize an unprecedented crystalline fullerene-based 2D metal halide semiconductor, namely (C60-2NH3)Pb2I6, (C60-2NH3 = bis(2-aminoethyl) malonate-C60), as a benchmark material to shed light on the interactions among semiconducting heterostructures. [4] To the best of our knowledge, this is the first report of a fullerene-based metal halide semiconductor in single-crystal form (excluding van der Waals heterostructures), and it was regarded by many as an improbable material to synthesize. We consider this compound to set the foundation of a new family of materials, namely, crystalline fullerene-based metal halide semiconductors (FMHS), with applications beyond photovoltaics to capacitors, catalysis and sensors.

References

1. A. Azmy, S. Li, G. K. Angeli, C. Welton, P. Raval, M. Li, N. Zibouche, L. Wojtas, G. N. M. Reddy, P. Guo, P. N. Trikalitis, I. Spanopoulos, "Porous and Water Stable 2D Hybrid Metal Halide with Broad Light Emission and Selective H2O Vapor Sorption", Angew. Chem. Int. Ed. 2023, 62, e202218429
2. A. Azmy, X. Zhao, G. K. Angeli, C. Welton, P. Raval, L. Wojtas, N. Zibouche, G. N. Manjunatha Reddy, P. N. Trikalitis, J. Cai, I. Spanopoulos, "One-Year Water-Stable and Porous Bi(III) Halide Semiconductor with Broad-Spectrum Antibacterial Performance," ACS Appl. Mater. Interfaces 2023, 15, 36, 42717–42729.
3. A. Azmy, A. B. Anderson, A. Mishra, E. Lo, N. Tariq, I. N. Gkikas, B. Sauval, N. Giunto, A. Kaur, S. Krzypkowski, N. Zibouche, G. P. Philippidis, I. Spanopoulos, "Unravelling the Impact of Porosity on Water Stability of Porous Bi(III) Halide Semiconductors and Their Potential for Red Tide Mitigation", Chem. Mater. 2025, 37, 8636-8648
4. W. Shen, A. Azmy, G. Li, A. Mishra, Z. Syrgiannis, W. Zheng, G. Volonakis, M. Kepenekian, J. Even, L. Wojtas, C. Wang, L. Huang, W. Chen, S. Zhou, J. Zhou, G. Zeng, D. Pu, H. Guan, G. Fang, W. Ke, I. Spanopoulos, “A Crystalline 2D Fullerene-Based Metal Halide Semiconductor for Efficient and Stable Ideal-bandgap Perovskite Solar Cells”, Adv. Energy Mater. 2024, 2400582, 1-12.

Bio:

Ioannis D. Spanopoulos received his BSc in Chemistry and MSc in Environmental Chemistry and Technology from the National and Kapodistrian University of Athens. In 2015, he earned his PhD in Materials Chemistry from the University of Crete, where his doctoral research focused on the development of metal–organic frameworks for gas storage and separation applications. In 2016, he joined the research group of Prof. Mercouri G. Kanatzidis at Northwestern University as a postdoctoral fellow, working on the design and synthesis of perovskite materials for optoelectronic applications. In 2021, he began his independent academic career as an Assistant Professor in the Department of Chemistry at the University of South Florida. Dr. Spanopoulos has received multiple awards and honors, including the 2020 IIN Outstanding Researcher Award from the International Institute for Nanotechnology, the 2022 ACS PRF Doctoral New Investigator Research Award, the 2024 DOE Early Career Research Program (ECRP) Award, the 2024 High Impact Practices (HIPs) Excellence Award, the 2025 Global Excellence in Research Award, and the 2025 Outstanding Research Achievement Award from USF. He was recognized as an Emerging Investigator from the Journal of Materials Chemistry A, a Rising Star from Advanced Optical Materials and ACS Organic & Inorganic Au, a Fellow of the International Association of Advanced Materials (IAAM) and is the author of over 100 publications across multiple disciplines, with more than 9,500 citations. Research at the Spanopoulos Group focuses on implementing molecular and crystal engineering to design and synthesize next-generation, multi-functional materials for medical, energy, and environmental applications. The group recently reported two new families of materials, the Porous Metal Halide Semiconductors (PMHSs) and the crystalline Fullerene-based Metal Halide Semiconductors (FMHSs).