CAREER: Manipulating Photon Energy by Perovskite-Sensitized Solid-State Upconversion

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Nontechnical DescriptionSolar energy is crucial to continue to meet the energy demands of today’s society. One pathway toward increasing the performance of solar cells is to increase the portion of sunlight that can be used to generate electricity. Much of the sun’s light is wasted because it consists of low-energy photons which are not absorbed by the semiconductors used to make solar cells. Low energy photons can be made usable by transforming them into higher energy photons through a process called upconversion. For example, two low-energy infrared photons can be converted into a higher-energy visible photon. This project will use a combination of organic molecules known to enable the upconversion process and metal halide perovskites, which are currently being investigated for use in solar cells. The perovskite will be used to absorb the low energy light and excite the organic molecules. Upon successful upconversion, higher energy light can then be absorbed for use in a solar cell. A combination of optical techniques and microscopy will lead to a detailed understanding of the underlying processes. Beyond the scientific impact of this project, a goal is to guide students to further pursue a scientific career and inspire their independent research, critical thinking, and creative problem-solving capabilities by strong mentorship in undergraduate research and education. This activity aims to inspire a new generation of scientists. To close the growing rift between scientists and the non-scientific community, a strong foundation linking the PI’s institution with the local community will be built by outreach lectures and science communication (‘Kitchen Chemistry’ or ‘Kitchen Spectroscopy’) via local TV and social media outlets.Technical DescriptionEfficient interconversion of solar energy to chemical or electrical energy is the key to meeting the future energy demands of our society. Improved photon utilization through an upconversion process involving triplet generation at the perovskite/organic semiconductor interface is a very promising approach to increase the photoexcited state lifetime and therefore, overall device efficiencies. The principal investigator will explore perovskite-sensitized solid-state upconversion via triplet-triplet annihilation to unravel the role of microscale and nanoscale molecular arrangement in OSCs. A combination of optical spectroscopy and scanning probe microscopy will be employed to elucidate the local optoelectronic properties originating from specific molecular arrangements of polyacenes on perovskite substrates. Control over orbital coupling by molecular placement will allow the involved steps to be systematically evaluated. The main goal is to understand why commonly utilized annihilators which exhibit high efficiencies in solution (e.g., diphenylanthracene) do not yield transferable results in the solid state, and how aggregation effects can be harnessed or avoided to improve solid-state upconversion yields. To achieve this goal, new perovskite/triplet acceptor pairs will be developed to investigate why promising solution-based triplet annihilators perform poorly in the solid state. The effect of local intermolecular interactions on the upconversion process will be studied on the microscale and the nanoscale using optical scanning probe microscopy and time-resolved optical spectroscopy. The combination of characterization methods spanning from the ensemble to the atomic scale will reveal the local structure-property relationships governing the bulk optoelectronic properties of hybrid perovskite/OSC-based TTA upconversion.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.