Jean-Luc Bredas

Regents Professor

Research

Harnessing Solar Energy with Organic and Hybrid Perovskite Photovoltaic Cells

Organic solar cells (OSCs) are currently attracting significant interest due to a number of appealing characteristics such as low cost, low environmental impact, solution-processing ability, conformability, and large-area manufacturing capability. Recent advances in the design of new electron-donor and electron-acceptor materials, optimization of the active-layer morphology, device engineering, modeling, and other disciplines resulted in the development of OSC devices with power conversion efficiencies over 18% in single-junction cells. By exploiting an integrated approach that combines quantum-chemical calculations based on density functional theory, theoretical modeling, molecular dynamics simulations at atomistic and coarse-grained levels, and kinetic Monte Carlo simulations, our studies focus on establishing chemical structure–morphology–electronic properties–performance relationships. We are currently interested in OSCs where the active layers are based on binary or ternary blends of polymer donors with small-molecule nonfullerene acceptors. We address a number of fundamental issues related to the description of the photo-excited states, and the processes of charge separation and charge recombination at the donor/acceptor interfaces as well as of energy and charge transport in the active layer.

Thermal Imaging with Sulfur Copolymers

Sulfur is one of the most abundant elements on the earth and plays a crucial role in various biological processes as a component of proteins and redox agents. They are being produced in large quantities as a byproduct of petroleum refining, but their technological applications are limited. However, recent development of polymers with high sulfur content has emerged as a promising solution for energy, environment, and healthcare challenges. Our group is contributing to the ongoing DMREF effort by developing sulfur and organic comonomer-derived polymers for thermal IR imaging applications using a combination of theoretical and computational methods including reactive-force field-based MD and machine learning approaches.

Hybrid Organic-Inorganic Perovskites

Perovskite-based organic-inorganic materials with varying dimensions (from 3D to 2D, 1D and 0D) have emerged as a new material platform with applications as thin-film solar cells and light-emitting devices. These materials combine organic molecular cations with inorganic (BX6) anionic octahedra (where B is usually Pb, Sn, or another metal; and X, a halide), which form corner-, edge-, or face-sharing crystalline structures. Our current computational studies focus on: (1) evaluating the electronic and vibrational couplings between the organic and inorganic components in low-dimensional perovskites that are expected to result in hybrid excitonic states or Dexter-type energy transfers; (2) understanding the defect physics, chemistry, and Sn oxidation mechanisms in Sn-based perovskite materials; (3) understanding the evolution of geometric and electronic structures in 2D perovskites induced by varying the perovskite layer thickness and ligand functionalization.

Two-Dimensional π-Conjugated Networks  

In two-dimensional (2D) covalent organic frameworks (COFs), monomer cores and linkers organize to form well-defined periodic structures via covalent bonds. The topology derives from the directionality of the covalent linkages, which offers a means to organize chemical functionality with atomic precision over long distances. The vast structural diversity of organic -conjugated moieties provides great opportunities in terms of designing and tailoring novel properties in 2D polymer networks. These emerging materials show great promise for applications including optoelectronic and spintronic devices, molecular recognition and sensing, catalysis, or membranes. Work in our group focuses on predicting and theoretically characterizing the novel electronic, magnetic, optical, and quantum topological properties that could be derived from free-standing single-layer and multi-layer 2D COFs, as well as from their interactions with metal, graphene, and transition metal dichalcogenides surfaces.

Organic Light-Emitting Diodes (OLEDs)  

Organic light-emitting diodes (OLEDs) are revolutionizing the consumer electronics market, as they offer high-quality displays for smartphones, laptops, televisions, and wearable devices, as well as solid-state lighting solutions. Our research aims to develop a comprehensive understanding of the electronic and optical processes taking place within OLEDs, with the goal of further improving their efficiency. This includes investigating charge and energy transfer, aggregation effects on electronic structure, thermally activated delayed fluorescence, hyperfluorescence, and the use of neutral radical-carrying organic emitters.

Hybrid Electrical-Ion Transport of Organic Polymer-Electrolyte Systems

Hybrid electrical-ionic transport has gained widespread focus in the frontiers of electronics research including the areas of optoelectronics, energy storage and catalysis. The π-conjugated hairy-rod type polymer N2200 offers new design paradigms suited for next-generation organic active materials. Realizing precise control of film microstructure to fine-tune desirable properties during fabrication is a feat that is of critical importance, however, a one that is hurdled by limited experimental in situ probing techniques. In Bredas laboratory, we exploit multi-scale modeling and simulations to uncover critical structure-property relationships of polymer-electrolyte interphases. The atomic and molecular scale insight that is obtained are in turn used in deriving ubiquitous protocols and guidelines for accelerating materials discovery, and effective film-morphology control during fabrication.

Morphology and Processing  

The importance of microstructure and morphology in polymer related fields is crucial, as these aspects significantly impact the functionality and sustainability of the used materials. A comprehensive understanding of these characteristics is essential for advancing polymer applications across various sectors, including electronics, biomedicine, and renewable energy. Our research team concentrates on advancing our understanding of the interplay between the chemical structure of active components, solvents, additives, temperature-dependent aggregation, and post-deposition processing steps in determining the thin-film morphology and stability of active layers in organic photovoltaic devices.

Additionally, we aim to unveil the impact of polymer structure, polymer-solvent interactions, and non-equilibrium effects during processing on the aggregation state and assembly pathways of conjugated polymers. By leveraging side-chain interactions and solvent quality, we intend to direct ordering during processing and enhance the stability of kinetically formed structures post-processing. The results of our research facilitate the understanding and designing conjugated-polymer based materials, generating novel assembled structures, and developing new manufacturing approaches to enhance device properties.