Emergent Opto-Mechanical and Electro-Mechanical Coupled Behavior of Halide Perovskites

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Nontechnical DescriptionSo-called ‘halide perovskites’ are a family of materials at the heart of a new type of solar-cell technology. These new solar cells are showing great promise as they are not only highly efficient in converting sunlight into electricity but also potentially very inexpensive to manufacture. However, the mechanical properties of these new solar cell materials are not known, especially under operating conditions of a solar cell: in sunlight, and also when electric current is passing through them. Thus, it is very important to study and understand these properties because they determine the long-term durability of the new solar cells, which are expected to operate efficiently for twenty years or more in the element. To that end, systematic research is conducted, where the following relevant mechanical properties of the new solar cell materials are studied under light and/or electric current: (1) cracking and healing of the cracks; (2) plastic deformation; and (3) time-dependent deformation. These studies are conducted on materials of well-defined chemical compositions, configurations, and morphologies. The results from these studies are analyzed critically to understand the behavior of the new solar cell materials. This is expected to have a broad impact on the ability to make highly durable, low-cost solar cells of the future, and to help this new solar-cell technology then reach its full potential. As part of this effort, underrepresented minority undergraduate researchers from Tugaloo College are trained. This leverages the fifty-year old partnership between Brown University and Tugaloo College -- an Historically Black College or University. The public outreach effort is aimed at enhancing the public's understanding of concepts in science, engineering, and technology. This entails leveraging the well-established science cartoons (SciToons) program at Brown University for creating two new SciToons on: ‘Emerging Solar Cells Technologies’ and ‘Strength of Materials.’Technical DescriptionThere are compelling reasons to suggest there are fascinating, rich opto-mechanical and electro-mechanical coupled behavior in halide perovskite materials, yet there is extreme paucity of research in this area. Considering the unprecedented promise of halide perovskites for new types of solar-cell and other devices, it is imperative to have a more in-depth understanding of the mechanical degradation of halide perovskites coupled with optical and/or electrical stimuli that are ubiquitous in devices. To that end, this project comes at a highly opportune time, and it entails four interrelated Tasks, and several Subtasks within. In Task 1, the effect of electric field on the fracture and crack-healing behavior in halide perovskite single-crystals and thin films is studied experimentally and quantified. Task 2 involves the quantitative study of plastic deformation of halide perovskite single-crystals, and the effect of light (photoplasticity). In Task 3, the effect of electric field on the time-dependent creep deformation of halide perovskite bulk polycrystalline pellets is studied. The efficient generation of photocarriers and facile ion migration in soft halide perovskites are expected to mediate crack-healing, plasticity, and creep phenomena, through their interactions with point and line (dislocations) defects in halide perovskites. Finally, in Task 4 the manifestation of photoplasticity effects, as an example, are demonstrated in devices. The considerable research infrastructure needed for the project developed at Brown University is leveraged fully. This research contributes to the scientific foundation for the development of next-generation perovskite solar-cell and other devices that are more efficient, and importantly more durable over the long term. As such, this research is expected to be highly impactful, and useful to researchers and technology developers alike.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.