SEERC FUNDED PROJECTS:
Advanced Materials

FISCAL YEAR 2011 ($122,259.00)

1. Enhanced Visible Light Absorption in Thin Film Multicrystalline Si Incorporated with Nanocrystals ($37,000)

FISCAL YEAR 2010 ($118,916.00)

1. Evaluation of Hydrogen Storage Capacity of Novel Nanomaterials Through
   Molecular-Level Modeling ($0)

FISCAL YEAR 2009 ($172,808.00)

Fiscal Year 2011 ($122,259.00)

Description

Through fundamental research, an interdisciplinary group of soft-materials scientists are developing methods to create nanoscale structures that are needed to efficiently transform solar energy to electricity with organic photovoltaic materials. In organic photovoltaics, it is critical that the material consist of two phases, one that creates an electron and one that can transport that electron to the electrodes to create an electrical current.  Moreover, there are limitations on the size of these domains (ca. 10 nm).  Unfortunately, there exist difficulties in predictably and reproducibly creating these nanoscale structures, thus our efforts focus on providing the fundamental understanding needed to guide the formation of organic photovoltaic materials with these targeted nanoscale structures.

These efforts have focused on exploiting the powerful potential of the self-assembly of diblock copolymers and the naturally optimized process of photosynthesis to create novel organic materials that can readily be incorporated into the next generation of photovoltaic devices.  For instance, biologically based materials are under investigation, such as the encapsulation of photosystem I in diblock copolymer matrices to create sustainable organic photovoltaic devices (Fig. 1). Additionally, the self-assembly of diblock copolymer (BCP) to form nanoscale microphases (Figure 2 top) is under investigation to create the nanoscale structrures needed for efficient photovoltaics. Similarly, when placed near a surface, the affinity of each half of the BCP for the surface controls its microphase structure, and this controllable phenomenon is utilized to induce the desired interconnected morphologies for a broad range of systems (Figure 2 bottom).

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Self-Consistent Field and Single Chain in
Mean-Field Simulations of Diblock and
Triblock Copolymer Systems

Participants

Faculty:
Brian Edwards (Chemical and Biomolecular Engineering; Lead)
Bamin Khomami (Chemical and Biomolecular Engineering)

Postdoctoral Fellow: Xianggui Ye
Visitor: Pavlos Stephanou

Description

One particular area of research that could have a major impact on the future of energy technology is that of self-assembling diblock and triblock copolymer systems, where can be used to tailor nanoscale structures that combine the beneficial characteristics of the various architectural blocks.  For instance, one block can induce stable film formation on a substrate, and another block can provide the deposited film with electronic properties for energy production, storage, and transfer.  Key features of these materials are the control of homogeneity, pattern formation, density, and physical dimensions of integrated circuits.
The most common approach to simulation is the self-consistent field (SCF) method.  The essential feature of this approach is the substitution of the interactions between all copolymer macromolecules with a system of noninteracting copolymers subject to external fields, which are position dependent and which act to determine the copolymer conformations, densities, etc., within the sample.  Despite the advantages of SCF methodology, there are some critical phenomena that are missing that are of relevance to the design of patterned nanoscale devices.  Primarily, density fluctuations are ignored in SCF, and these can actively participate in determining the properties of the diblock system.  Single-chain in mean-field (SCMF) simulation methodology was developed to retain the computational feasibility of the SCF approach, yet to include relevant fluctuation effects in the overall system description.  In this project, we develop the necessary expertise, computational algorithms, and simulation techniques to apply SCF and SCMF simulations to materials of interest and relevance to the challenges facing sustainable energy harvesting in the future. 

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Heavy-Atom Molecular Structure Effects
on Photovoltaic Response in Organic
Solar Cells

Participants

Faculty: Bin Hu (Materials Science and Engineering)

Graduate Students:
Huidong Zang (Materials Science and Engineering),
David White (Materials Science and Engineering)

Description

This project plans to use our unique experimental tool magnetic field effects of photocurrent together with polarization-induced photoluminescence quenching to investigate how heavy-atom molecular structure affects the key photovoltaic process: exciton dissociation and exciton recombination in organic solar cells. The goal is to reveal why triplet states can increase photovoltaic response in organic materials.
The proposed experiments include (i) magnetic field effects of photocurrent together with polarization-induced photoluminescence quenching and (ii) the modification of heavy-atom molecular structure. Specifically, magnetic field effects of photocurrent together with polarization-induced photoluminescence quenching will be used to elucidate how heavy-atom molecular structure changes singlet and triplet exciton dissociation and recombination. The modification of heavy-atom molecular structure will be done by dispersing phosphorescent molecules into photovoltaic polymer matrices based on inter-molecular electrical and magnetic interactions. These two experiments have been already developed in our research of organic spintronics. The project will deliver critical understanding of effects of heavy-atom molecular structure on singlet and triplet photovoltaic processes in organic solar cells.

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Enhanced Visible Light Absorption in Thin
Film Multicrystalline Si Incorporated with
Nanocrystals

Participants

Faculty:
Ramki Kalyanaraman (Materials Science and Engineering and Chemical and Biomolecular Engineering; Lead),
Gerd Duscher (Materials Science and Engineering and ORNL),
Philip Rack (Materials Science and Engineering)

Graduate Student: Ritesh Sachan (Materials Science and Engineering)

Description

The goal of this interdisciplinary and collaborative research activity is to enhance visible light absorp­tion in ultrathin films of multicrystalline (MC) Si by incorporating nanocrystals chosen to provide strong spectrally-tailored response within Si. Solar cells made from thin film MC-Si are viewed as an important photovoltaic material for future use in large-area sustainable energy applications, such as in solar panels requiring low cost, high efficiency and flexibility. Presently, the poor absorption of Si in the visible wave­lengths limits its use in such applications. Recent works have suggested that appropriately chosen nanopar­ticles placed inside MC-Si can enhance absorption in visible wavelengths. However, the strong chemical reactivity of most materials with Si makes the selection and fabrication of such MC-Si nanocomposite films a challenging task. In this work, we will combine theoretical models of optical mixing with materials pro­cessing considerations to design MC-Si nanocomposite films. Promising MC-Si nanocomposites will be fabricated utilizing thin film and processing techniques, including by sputter deposition and laser anneal­ing. The nanoscale structure and interfaces in the resulting nanocomposites will be investigating utilizing high-resolution electron and scanning microscopies and will be correlated with optical reflection and trans­mission characteristics of the films. From this integrated activity we anticipate an improved understanding of the role nanocrystals embedded inside MC-Si could play on enhancing solar energy absorption within such MC-Si thin films.

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