My PhD research has primarily focused on novel measurement techniques to probe mechanisms of charge transport and recombination in organic bulk heterojunction (BHJ) solar cells.  Most researchers use a typical vertical device structure to study transport in organic photovoltaic (OPV) cells but this structure has many limitations.  Instead, we have developed a lateral structure where we can study charge carriers traversing OPV devices of various lengths.  The variation in device length has given us the ability to measure the mobility-lifetime product and generation rate of charge carriers in these devices.  The mobility-lifetime product in OPV cells is the primary figure of merit to characterize the movement of charge carriers BHJ solar cell devices.  Additional studies to determine the effect of light intensity, light spectrum, electric field, and temperature on the mobility-lifetime product have begun to provide insight on recombination mechanisms, the mobility of the charge carrier, and the carrier's lifetime.  The incorporation of additional measurement techniques on lateral solar cell devices is also planned to further probe transport and recombination mechanisms in these materials.

In addition to transport studies, we have begun to work with a small business to develop inkjet printable OPV cells on flexible substrates.  These OPV cells will provide power to a wireless communication system and other microelectronic devices based on a inkjet printable architecture.  Currently, we are optimizing commercially available materials and device architectures in order to integrate the OPV cell and the communication system into a fully automated manufacturable process that is compatible with flexible electronic systems.

Copper indium diselenide (CIS) and a related material copper indium gallium selenide (CIGS) have been actively researched for over 20 years and researchers have made solar cells with efficiencies nearing 20%.  In order to reduce the cost of these materials and add potential for commercialization, we have collaborated with a group that synthesized CIS nanoparticles from solution.  Transport studies of nanoparticle films of CIS reveal variable range hopping transport in this material.  In addition to transport studies, solar cells based on CIS nanoparticles have been fabricated and have exhibited efficiencies currently exceeding 3%.

Refereed Publications

1. Lombardo, C., E. Danielson, and A. Dodabalapur, Examining charge transport and recombination in the bulk heterojunction solar cells using a lateral solar cell geometry. Journal of Applied Physics, 2011. Under Preparation.
2. Lombardo, C., Z. Ooi, B. Cobb, E. Danielson, and A. Dodabalapur, Measurement of the mobility-lifetime product in bulk heterojunction organic photovoltaic materials. Organic Electronics, 2011. Under Preparation.
3. Lombardo, C., V. Akhavan, M. Panthani, B. Goodfellow, B. Korgel, and A. Dodabalapur, Temperature-Dependent Charge Transport in Copper Indium Diselenide Nanocrystal Films. Applied Physics Letters, 2011. Under Preparation.
4. Lombardo, C. and A. Dodabalapur, Nongeminate carrier recombination rates in organic solar cells. Applied Physics Letters, 2010. 97(23): p. 233302-3.
5. Lombardo, C. and A. Dodabalapur. Using bulk heterojunction field effect measurements to understand charge transport in solar cell materials, in Organic Photovoltaics and Related Electronics—From Excitons to Devices, edited by V.R. Bommisetty, N.S. Sariciftci, K. Narayan, G. Rumbles, P. Peumans, J. van de Lagemaat, G. Dennier, S.E. Shaheen (Mater. Res. Soc. Symp. Proc. Volume 1270, Warrendale, PA, 2010), 1270-GG10-02.

Conference Publications and/or Presentations

1. Dodabalapur, A., C. Lombardo, and E. Danielson, Charge Transport and Recombination in Organic Bulk Heterojunctions. 2011: Montreal, Quebec.
2. Lombardo, C., E. Danielson, and A. Dodabalapur, Studying recombination in the bulk heterojunction solar cells using lateral solar cell geometries, in American Physical Society March Meeting. 2011: Dallas, TX.
3. Danielson, E., C. Lombardo, and A. Dodabalapur, Scaling behavior and transport in bulk heterojunction materials, in American Physical Society March Meeting. 2011: Dallas, TX.
4. Lombardo, C., E. Danielson, and A. Dodabalapur. Examining charge transport and recombination in the bulk heterojunction solar cells using a lateral solar cell geometry. in Materials Research Society Fall Meeting. 2010. Boston, MA.
5. Lombardo, C., E. Danielson, and A. Dodabalapur, Application of field-effect device structures in the study of charge transport and recombination in bulk heterojunction materials systems, in SPIE Photonic Devices + Applications. 2010: San Diego, CA.
6. Dodabalapur, A., C. Lombardo, and E. Danielson, Liquid Crystals for Renewable Energy, in Workshop on Directing Nanoscale Organization in Organic Photovoltaics, Solar Cell Workshop. 2010: Boulder, CO.
7. Lombardo, C. and A. Dodabalapur. Using bulk heterojunction field effect measurements to understand charge transport in solar cell materials. in Materials Research Society Spring Meeting. 2010. San Francisco, CA.
8. Chisolm, R., N. Craik, and C. Lombardo, Community Partnership, in Engineers Without Borders South Central Regional Workshop. 2009: Normon, OK.
9. Lombardo, C. and K. Alexander, Plan B: Achieving Success after Unforeseen Setbacks, in Engineers Without Borders International Conference 2009: Milwaukee, WI.
10. Mitra, R., E. Chmela, J. Delgado Vela, and C. Lombardo, Computers and Internet for Education: Northern Coahuila, Mexico, in Engineers Without Borders International Conference. 2009: Milwaukee, WI.
11. Lombardo, C., A. O'Neill, and P. Kulis, Turning Road Blocks into Successes, in Engineers Without Borders International Conference. 2008: Seattle, WA.
12. Jeong, Y., C. Lombardo, D. Duarte, and A. Dodabalapur. Surface-Treatment Effects on the Pentacene-Based Organic Field-Effect Transistors with Anodized Gate Dielectrics. in American Physical Society March Meeting. 2008. New Orleans, LA.

Unrefereed Publications

1. Ervin, M., S. Kilpatrick, C. Lombardo, B. Nichols, A. Perrella, and A. Wickenden, The Present State of Amperometric Nanowire Sensors for Chemical and Biological Detection, A.R.L. Sensors and Electron Devices Directorate, Editor. 2006: Adelphi, MD.