Uncovering Energy and Charge Transport Mechanisms in Organic-Inorganic Hybrid Perovskite Quantum Wells with Nonlinear Action Spectroscopies

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WIth support from the Chemical Structure, Dynamics & Mechanisms-B (CSDM-B) Program and the Chemical Measurement and Imaging (CMI) Program of the Division of Chemistry, Wei You and Andrew Moran of the Department of Chemistry at the University of North Carolina at Chapel Hill are developing two-dimensional organic-inorganic hybrid perovskite (2D-OIHPs) materials for their potential use in solar cells. In these materials, layers of organic molecules confine photoexcited electrons within inorganic metal-halide sheets termed “quantum wells.” The goal of this research is to enable long-range electron transport in such 2D-OIHP based solar cells by tuning the electronic structures of the interstitial organic layers using derivatives of tetrazine molecules. Materials developments will be guided by direct measurements of electron velocities with newly developed laser spectroscopies. The project lies at the interface of physical and materials chemistry. Graduate student education and outreach activities involving K-12 students are integral parts of this project. Two-dimensional organic-inorganic hybrid perovskites (2D-OIHPs), in which organic cations and inorganic halide frameworks are assembled in an alternating manner into a layered structure, have been intensively studied due to their unique optoelectronic properties. The inorganic phases of these systems (i.e., quantum wells) exhibit properties that depend on the number of stacked metal-halide octahedra and interactions with the organic layers. In the proposed work, derivatives of tetrazine will be incorporated into 2D-OIHPs to promote out-of-plane electron transfer processes by varying donor-acceptor interactions and distances between neighboring quantum wells. The team hypothesizes that out-of-plane electron transfer will be facilitated by aligning the LUMO levels of tetrazine spacer molecules with the conduction band minima of the quantum wells. In addition to conventional techniques, the team will apply newly developed, multidimensional “action spectroscopies” to distinguish energy and charge transport dynamics in these systems. This collaborative proposal leverages the complementary expertise of research groups who specialize in (i) materials synthesis and device fabrication as well as (ii) the development and application of multidimensional laser spectroscopies.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.