May 19, 2008

2009 Joint NSLS-CFN Users' Meeting Workshop

Nanostructured Photovoltaic Materials and Devices

2009 was the first year for a workshop focused on nanostructured photovoltaic materials and devices. The workshop, which was organized by Brookhaven's Center for Functional Nanomaterials (CFN), was well attended throughout the entire event.

CFN Director Emilio Mendez started the workshop with some welcoming remarks, including describing the CFN mission and encouraging everyone in attendance (speakers and audience) to explore ways to further engage with CFN in pursuing scientific research goals. Workshop organizer Charles Black followed Mendez by describing workshop organizational details, including the day’s agenda. Black served as moderator for the four workshop technical sessions.

Participants of the Nanostructured Photovoltaic Materials and Devices Workshop

The first morning session opened with a talk by professor Marc Baldo from the Massachusetts Institute of Technology. Baldo is the Principle Investigator of the Center for Excitonics, a newly funded Department of Energy (DOE) Energy Frontier Research Center led by MIT, with Harvard University and Brookhaven National Laboratory (CFN) as partners. Baldo spoke about the Center for Excitonics research goals, as well as examples from his own research program, including higher-performing luminescent solar concentrators.

Michael Pellin followed with an overview of his program at Argonne National Laboratory focusing on implementing atomic-layer deposition as a synthesis method for wide-bandgap oxides – a useful tool for fabricating highly nanostructured solar devices. Pellin is the Acting Materials Science Division Director at Argonne and leader of the Argonne-Northwestern Solar Energy Research Center, which was also recently awarded a DOE Energy Frontier Research Center.

The second morning session included two talks from CFN researchers Chang-Yong Nam and Raluca Gearba, both Goldhaber Distinguished Fellows at the Laboratory. Nam presented experimental results on understanding the effects of oxygen exposure on the performance of organic solar cells, including methods for achieving high performance in all-air-processed materials. Gearba also spoke about organic-based photovoltaic devices, and presented a new method from crosslinking poly-3-hexyl-thiophene that improves the electrical properties.

The first afternoon session opened with a talk by Seth Darling, an assistant scientist at the Center for Nanoscale Materials (CNM) at Argonne National Laboratory. Darling first presented an overview of the CNM, a sister institution to Brookhaven's CFN. He next described experimental progress using block copolymer thin film materials to self-organize the active semiconductor layer of an organic photovoltaic device, with a target goal of improving charge collection. Dr. Darling also presented work on a hybrid organic-inorganic solar device utilizing nanostructured TiO₂ (made by an anodization process) together with in-situ ultraviolet polymerized polythiophene. This work was performed in collaboration with professor Steve Sibener at the University of Chicago.

Professor Vladmir Bulovic (Massachusetts Institute of Technology) followed with a discussion of his group's recent research efforts in nanostructured photovoltaic devices. Bulovic described advantages of nanostructured photovoltaic materials, including tunable absorption spectra, efficient use of materials, and low-temperature (and cost) fabrication. In particular, he described quantum-dot-based solar cells having much-improved open circuit voltage (as high as 1.3V) – an important metric for overall performance efficiency. Tandem versions of these devices have open circuit voltages as high as ~2.5V.

Next, David Mitzi from the IBM Thomas J. Watson Research Center presented an overview of his research efforts at solution-phase processing of copper-indium-gallium-sulfide (CIGS) –based solar cells. Thin-film cells using CIGS have reached performance efficiencies of up to ~19 percent in the laboratory and 10 percent in modules. The idea behind Mitzi's research is to replace vacuum based techniques of depositing layers with solution methods. He described techniques of precursor formation and recipes for thin-film processing, and reported device performance efficiencies of nearly 13 percent using solution-phase methods. Mitzi also discussed similar devices using copper-indium-sulfide (CIS) materials, with performance efficiencies of order 10 percent.

For more information:
Charles Black
Brookhaven National Laboratory
Center for Functional Nanomaterials
Email: ctblack@bnl.gov