The performance (i.e., light harvesting, optical gain or emission outputs) of many optoelectronics devices (i.e., lasers, photovoltaics (PVs), light emitting diodes (LEDs), etc.) critically depends on the ability to deposit solution processed nanocrystals (NCs) into well-organized, close-packed solids with high photoluminescence quantum yields (PL QYs) and the long term stability of NC films. However, irrespective of the high quality of NCs or the passivation techniques used in solution, the deposition of NC multilayers as well as the exposure to the environment during solid state device fabrication often require or lead to changes in the NCs chemical environment, such as exchange/loss of ligands, which eventually leads to formation of trap states that decrease the PL QYs of NCs and are often detrimental to device performances. An attractive approach to protect the NCs’ integrity is the use of atomic layer deposition (ALD) in which self-limiting surface reactions of the precursors allow conformal growth of the metal oxide layer with precise thickness control to encapsulate NCs. This process, though preventing the deterioration of NCs, is observed to decrease their PLQY significantly. To mitigate this issue, we recently developed an alternate gas phase deposition technique where a pulsed co-deposition of both metal and oxidant precursors at room temperature (RT) (reminiscent of chemical vapor deposition, CVD) is able to deposit uniform metal oxide (AlO<sub>x</sub>) films, originating from gas-phase reactions in the immediate vicinity of the NC layer. Unlike conventional ALD, this method preserves the optical properties, e.g., PLQY and lifetimes of metal chalcogenide NCs films. With this new approach, we investigate the encapsulation of metal halide perovskite NCs, which have been at the forefront of recent optoelectronic materials research due to their high absorption coefficients, high charge carrier mobilities, balanced ambipolar transport properties, and easy solution processability. However, in spite of the exceptional upsurge in the lab scale device efficiency of perovskites in a remarkably short time frame, the practical application of the same in real world is restricted by their inherent instability. AlO<sub>x</sub> deposition on perovskite nanocrystals with our modified approach not only retains the optical properties of the NCs, but also improves them, even at a single particle level, which paves the way for their unique optoelectronic opportunities.

Encapsulation of perovskite nanocrystal solids using metal oxides: A closer look into optical properties

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.