Atomic-Level Insight into Photoinduced Transformations in Perovskite Optoelectronics

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The climate emergency makes the search for new more efficient energy materials imperative. Metal halide perovskites (MHPs) belong to a class of materials promising highly efficient, affordable, and lightweight solar cells and light emitting diodes. One of the key challenges is that these materials are remarkably sensitive to ambient conditions and readily undergo chemical transformations in the presence of oxygen, humidity and under illumination. While these processes can be either pernicious or beneficial, very little is known about their atomic- level mechanism, which makes it difficult to rationally design mitigation strategies. PhotoPeroNMR sets out to address this challenge by using a combination of highly efficient synthetic approaches and solid-state Magic Angle Spinning (MAS) Nuclear Magnetic Resonance (NMR). The project will study the reactivity of MHP surfaces with ambient gases, identify the chemistries of the surface species across a wide range of structurally diverse materials relevant to optoelectronics, including lead and lead-free perovskites and double perovskites. Next, it will develop a strategy to access atomic-level (local) structural data from MHPs in their form directly relevant to optoelectronics, intact optoelectronic devices. It will develop a strategy to illuminate MHPs in a variety of atmospheres and study the microscopic mechanism of the resulting transformations. Finally, it will elucidate the local structural changes taking place in devices under illumination using operando NMR. The combined knowledge obtained here will serve to formulate rational design principles enabling the design of passivation agents with improved characteristics. This local structure characterization framework will provide an underpinning microscopic insight into the most successful materials, naturally combining the effects of intentional and unintentional surface passivation, photoinduced effects, and interactions with the neighboring device layers.