Speakers

Prof. Kai ZHU is currently a senior scientist in the Chemistry and Nanoscience Center at the National Renewable Energy Laboratory (NREL). He received his PhD degree in physics from Syracuse University in 2003, where he studied the electrical & optical properties and device physics of solar cells based on amorphous-silicon thin films and dye-sensitized mesoporous TiO₂ films. He then spent about one year at Kansas State University as a postdoctoral researcher, working on III-Nitride wide-bandgap semiconductors for high-power blue and UV light emitting diodes. In 2004, he joined NREL as a postdoctoral researcher in the laboratories of Dr. Arthur J. Frank, working on fundamental charge carrier transport and recombination in photoelectrochemical cells, especially dye-sensitized solar cells. Since 2007, he has worked as a staff scientist at NREL.

Prof. ZHU’s current research interests are focused on both basic and applied research on perovskite solar cells, including perovskite material development, device fabrication and characterization, and basic understanding of charge carrier dynamics in these cells. In addition to solar cell applications, his research interests have also included hydrogen production via photoelectrochemical cells as well as nanostructured electrodes for Li-ion batteries and supercapacitors.

Efficient and stable perovskite solar cells enabled by surface engineering with bulky organic molecules

Abstract

Organic-inorganic hybrid halide perovskites have attracted significant R&D attentions in the photovoltaic community as a competitive future photovoltaic technology. The certified efficiency of single-junction perovskite solar cell (PSC) has reached near 26%. Using molecules or structures based on bulky organic cations (e.g., butylammonium or phenethylammonium) to improve the surface and interface properties have become a promising strategy to enhance both efficiency and stability of perovskite solar cells. However, significant issues still exist with the use of bulky organic molecules, including structure control, charge transport, bulk and surface morphology, and interfacial energy alignment. In this talk, I will discuss our recent studies on surface engineering of 3D perovskites by using structures based on bulky organic molecules. The use of bulky organic molecules often results in the formation of 2D perovskite structures, which usually exhibit significant transport barriers, especially in the out-of-plane transport direction. In addition, the use of bulky organic structures can disrupt the growth of 3D perovskites. A good understanding and control of the perovskite growth is critical to fully utilize the benefits associated with bulky organic molecules and related structures. I will present strategies based on our recent studies to suppress defect formation, improve bulk and surface morphology, and reduce transport barrier for better extraction. The physical and optoelectronic properties of perovskites can be affected by controlling the precursor chemistry and growth conditions. Some of our recent results on perovskite-based tandem devices will also be discussed.