The goal of IEC's research has always been to advance the development and acceptance of
thin-film photovoltaic modules. This research is often carried out in close collaboration with
and in support of (national) research teams. Our current technical objectives in each of four
thin film solar cell programs are as follows:
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I. CuInSe2-based Solar Cells
- Develop an understanding of the functioning and processing requirements for high-efficiency
Cu(In,Ga)(S,Se)2 cells with bandgaps from 1.3 to 1.7 eV.
- Explore and understand Cu(In,Ga)(S,Se)2 absorber formation limiting
reaction temperatures to approximately 400 C.
- Identify the critical requirements of all materials used in the device fabrication process
(glass, Mo, CdS, surface modification of Cu(In,Ga)(S,Se)2, ZnO, etc.)
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II. Amorphous Silicon
- Increase the short-circuit currents in the component cells of multijunction devices by reducing
optical losses and improving light-trapping.
- Optimize interfaces to improve Voc of component cells in multijunction devices.
- Quantify and reduce the optical and contact losses of multijunction devices as prioritized by
the a-Si Research Teams.
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III. CdTe-based Solar Cells
- Improve the understanding for the requirements of the CdS/CdTe junction using a thin CdS layer
and how this interface can be manipulated by altering the cell processing.
- Provide stability tests on CdTe cells and interpret the results found.
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IV. Thin poly-Si layers on low cost substrates
- Deposit thin Si layers by hot wire CVD on glass or other low cost substrates having large grains
and optoelectronic properties suitable for solar cells
- Fabricate and characterize devices with hot wire CVD Si absorber layers and c-Si or a-Si doped layers
- Develop and verify a kinetic model for gas phase and surface reactions leading to film growthThin poly-Si layers
on low cost substrates
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Research Facilities and Equipment
The IEC has established the equipment and capabilities required to conduct leading edge research
on thin film photovoltaic materials. Presently, our ability to deposit a wide range of materials is
made possible with the following equipment:
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- a rf plasma CVD reactor for depositing amorphous and microcrystalline
Si layers and solar cells
- a hot wire CVD reactor for depositing polycrystalline Si
- 3 multisource evaporators for depositing CdTe, Cu(In,Ga)Se2 ,
and CdS for polycrystalline thin film solar cells
- chemical bath deposition of CdS
- a selenization reactor for reacting Cu, In, and Ga layers with
Se
- a dc sputtering system for depositing Cu, In, Ga, Mo and Al
- a rf sputtering system for depositing ZnO, ITO, and Mo
- two electron beam evaporators for depositing a wide range of metals
- several ovens and furnaces for annealing and recrystallizing under
various chemical atmospheres
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In order to evaluate the wide range of materials deposited in
the above systems, it is necessary to
maintain an equally broad
array of equipment for characterization of the materials and the
solar
cells. IEC has the following measurement and analysis capabilities:
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- scanning electron microscope for structural analysis
- X-ray diffraction for structural and crystallographic analysis
- energy dispersive spectroscopy (or energy dispersive analysis
of X- rays) for compositional analysis
- atomic absorption spectroscopy for chemical analysis
- UV-VIS-IR optical spectrometer for analysis of optical properties
- four-point probe for resistivity measurement
- Hall effect for resistivity and mobility measurement
- temperature controlled current-voltage measurement for conductivity
and solar cell characterization
- laser scanning (or LBIC) for spatial uniformity of photoresponse
- calibrated solar simulator for solar cell performance testing
- spectral response for quantum efficiency measurement
- capacitance for junction characterization
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IEC has always made laboratory safety a major concern, and has
been a leader among university
solar cell research facilities
in this regard. We have an extensive interlocked system of hazardous
gas detection and containment with back-up power for ventilation.
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