Stable and Efficient Electroluminescent Devices Based on 3D / 0D Perovskite Bulk/Nanocrystal Emission Layers

Nontechnical Description The exceptional electronic and optical properties of metal halide perovskites (MHPs) have drawn great interest for their use in electronic devices such as solar cells and light-emitting diodes. However, the stability of devices based on perovskites is an outstanding problem. Low-dimensional, fully inorganic perovskites have the potential to address this issue. This project develops heterostructures made from light-emitting perovskite nanocrystals embedded in a bulk perovskite matrix. The matrix provides efficient charge transport, and the nanocrystals emit bright and saturated red, green, and blue light. Furthermore, these structures show enhanced stability in operating devices. The work involves understanding the synthesis of novel nanocrystals, processing semiconductor blends, and developing structures for highly efficient and stable devices. This outcomes of this project impact the development of energy efficient electronics, including displays, flexible electronics, and solid-state lighting. Students will gain training that spans physics, chemistry, photonics, and materials science and engineering. Furthermore, the project fosters connections to industrial projects and international collaborations, providing pathways for future STEM careers. Technical Description Perovskite materials combine the advantages of both organic and inorganic emitters, with narrow emission bandwidth, high color tunability (by halide choice), facile chemical synthesis, and excellent charge transfer properties. The primary reason for instability, however, lies in the predominantly “soft” ionic structure of traditional (3D) materials with corner-sharing octahedra surrounded by the organic cations residing in the voids, thus providing insufficient stability. To address these problems, the research team proposes to develop and utilize inherently more stable, zero-dimensional (0D) perovskite nanocrystals (NCs) without corner-sharing connectivity. The higher degree of localization leads to much-improved stability. Our synthesis of highly emissive cesium lead bromide and cesium lead iodide 0D NCs and their seamless incorporation into the 3D perovskite injection matrix opens the possibility of creating stable, efficient white-light light emitting structures. For that purpose, the investigators will design perovskite light-emitting chemical cells employing polymer electrolytes and salts to invoke differential ion motion. When blended with perovskite film, smaller additive ions move in place of the perovskite ones, preserving the underlying structure of perovskite and allowing for an efficient charge injection from a single-layer device. This leads to low-voltage devices with record operational stability and lifetime. Specifically, the team will develop various methods of uniform or layer-by-layer blending of 0D perovskite NCs into a 3D matrix and conduct extensive optical and electrical characterization to develop structures for use in efficient devices. These strategies will ultimately open numerous avenues to explore low-dimensional perovskite materials for high-performance emissive devices. Importantly, this research on the interface of several disciplines will be a catalyst for many students to choose highly advanced fields of nanotechnology and will benefit them by providing diverse backgrounds in physics and materials science. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.