Above: VHF plasma reactor
Photovoltaic Materials and Device Research
MRC scientists and students have established a world-class laboratory for research in photovoltaic(solar) energy conversion materials and devices. The program focuses on growth of thin film electronic materials suitable for photovoltaic conversion, and on fabricating devices in them. Current materials of interest include amorphous Si and its alloys, and CdTe.
A. Research on a-Si:H and its alloys
A-Si is deposited using a remote, reactive ECR plasma deposition, and after deposition, the films are characterized for their optical and electronic properties. The reactors can be used also to make doped layers and devices in these films. The devices are measured using solar simulators and other electronic measurement techniques, such as capacitance-frequency measurements and quantum efficiency measurements. This is an active research program, supported by National Renewable Energy Laboratory and by industry. ISU is one of the leaders in the world in this field.
Left: Activation energy setup
Another part of the a-Si program is a theoretical effort to understand the microscopic origins of defects in a-Si, using molecular dynamic simulations to simulate local Si-Si and Si-H bonds in the material, and their statistical distributions. The simulations also try to model the movement of H in these materials in response to energetic inputs, and see how these movements and bond-rearrangements affect the electronic properties.
This theoretical effort is complemented by experimental work to measure the diffusion of H and D in a-Si , a-(Si,C) and a-(Si,Ge) materials. It is known that diffusion of H plays a critical role in defect creation in these materials, and by using Secondary Ion Mass Spectroscopy, one can determine the diffusion kinetics of H and D, and correlate them with the defect structure in the material.
B. Semiconductor Process research
Production cost of solar electric conversion panels is the critical element which determines their commercial success. We work with a local company, Iowa Thin Film technologies, Inc.(ITFT), which is a spin-off from ISU, to improve the processing of solar cells. ITFT deposits these cells on polyimide substrates, in continuous deposition reactors using a roll-to-roll process. ISU scientists work with ITFT to understand the plasma processes that govern deposition, and on development of in-situ sensors for process controls and reliability.
Solar simulator
Faculty
Vikram Dalal
Staff
Ruth Shinar, Max Noack, Keqin Han
Students
Debju Ghosh, Viswas Jaju, Kamal Muthukrishnan, Dan Pates, Satya Saripali, Puneet Sharma, Nanlin Wang
Papers
Funding Agencies
