Speakers

Prof. Aleksandra B. Djurišić obtained Ph. D. degree in Electrical Engineering from the School of Electrical Engineering, the University of Belgrade in 1997. She has been a postdoctoral fellow at the University of Hong Kong and Alexander von Humboldt postdoctoral fellow at TU Dresden. She joined the department of Physics at the University of Hong Kong in 2003 as assistant professor and she is currently a professor. Her research interests include halide perovskite materials, nanomaterials, wide-bandgap semiconductors, and organic materials, and their applications in areas related to energy and environment, such as photocatalysis, solar cells, and LEDs. She has published 392 research articles including reviews, and has been cited over 22000 times. Her h-index is 66.

Towards improved efficiency and stability of metal halide perovskite devices using 2D perovskite materials

Abstract

Metal halide perovskite materials have been attracting great attention for applications in optoelectronic devices due to their outstanding properties. These hybrid organic- inorganic materials offer the possibility of combining low cost and simplicity of solution processing common for organic materials with high device efficiencies common for inorganic semiconductors. In a recent decade, the efficiencies of both perovskite solar cells (PSCs) and perovskite light emitting diodes (PeLEDs) have rapidly increased. While significant progress in device stability compared to early days of perovskite research has also been made, the stability of these materials still remains a problem that must be addressed before the metal halide perovskite devices can be commercialized. The intrinsic instability of commonly used 3D lead halide perovskite materials with a formula APbX₃ (A is a monovalent organic or Cs⁺ cation, X is a halide anion) upon exposure to ambient atmosphere, illumination, elevated temperature, and/or electrical bias limits the device stability since the exposure to bias, illumination, and elevated temperature is inevitable during device operation (ambient exposure can be mitigated with encapsulation).

While stability issues can be mitigated using optimized material composition and deposition conditions, defect passivating additives and interface modifications, for further improvements it is necessary to consider perovskite materials with improved stability. For this purpose, 2D and quasi-2D perovskites have been attracting increasing attention as they are generally more stable compared to 3D materials. These materials have a formula C_zA_n-1B_nX_3n+1 where C is monovalent (z=2) or divalent (z=1) bulky spacer cation, A is a small organic monovalent cation or Cs⁺, B is a divalent metal cation (commonly Pb²⁺), X is a halide anion, and n is the number of 3D perovskite layers which are separated from each other by spacer cations. The bulky spacer cations contribute to enhanced ambient stability and reduced ion migration, but also hinder the charge transport in the direction perpendicular to lead halide octahedral layers. In addition, the spin-coated films typically contain multiple n phases, resulting in complex film properties. Therefore, careful optimization of the perovskite composition and deposition conditions is necessary to achieve improved device performance. In this talk, I will first discuss the stability of different 2D perovskites, followed by the effect of 2D perovskite top layer on efficiency and stability of 3D/2D perovskite solar cells. This will include the selection of spacer cation, as well as overall effects of device architecture and interface modification layers on the performance. Then, the use of different quasi-2D perovskites in PeLEDs will be discussed. This will include different methods of controlling the phase composition, optimizing the charge transfer among different n phases and passivating defects. Finally, future outlook on the role of 2D perovskites in improving stability of PSCs and PeLEDs will be discussed.