Materials Optimization for Silicon Heterojunction Solar Cells Using Spectroscopic Ellipsometry
We have used hot wire chemical vapor deposition (HWCVD) to fabricate silicon heterojunction (SHJ) solar cells on p-type FZ silicon substrates with efficiencies as high as 18.2%. The best cells are deposited on anisotropically-textured (100) silicon substrates where an etching process creates pyramidal facets with (111) crystal faces. Texturing increases J{sub sc} through enhanced light trapping, yet our highest V{sub oc} devices are deposited on un-textured (100) substrates. One of the key factors in maximizing the efficiency of our SHJ devices is the process of optimization of the material properties of the 3-5 nm thick hydrogenated amorphous silicon (a-Si:H) layers used to create the junction and back contact in these cells. Such optimization is technically challenging because of the difficulty in measuring the properties of extremely thin layers. In this study, we have utilized spectroscopic ellipsometry (SE) and photoconductivity decay to conclude that a-Si:H films grown on (111) substrates are substantially similar to films grown on (100) substrates. In addition, analysis of the substrate temperature dependence of surface roughness evolution reveals a substrate-independent mechanism of surface smoothening with an activation energy of 0.28 eV. Analysis of the substrate temperature dependence of surface passivation reveals a passivation mechanism with an activation energy of 0.63 eV.
- Research Organization:
- National Renewable Energy Laboratory (NREL), Golden, CO.
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC36-08GO28308
- OSTI ID:
- 978495
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
36 MATERIALS SCIENCE
ACTIVATION ENERGY
CHEMICAL VAPOR DEPOSITION
DECAY
EFFICIENCY
ELLIPSOMETRY
ETCHING
HETEROJUNCTIONS
OPTIMIZATION
PASSIVATION
PHOTOCONDUCTIVITY
ROUGHNESS
SILICON
SOLAR CELLS
SUBSTRATES
Silicon Materials and Devices
Solar Energy - Photovoltaics
TEMPERATURE DEPENDENCE
TRAPPING