Device Physics of Thin-Film Polycrystalline Cells and Modules: Final Report, February 1998 -- August 2001

Technical Report · Tue Jan 01 00:00:00 EST 2002

DOI:https://doi.org/10.2172/15000241· OSTI ID:15000241

Sites, J R

This report describes the basic measurements of CdTe and CI(G)S solar cells fabricated at a number of collaborating laboratories. The first area of emphasis has been to quantitatively deduce the loss mechanisms in these cells, and to make appropriate comparisons that illuminate where progress in being made. Cells evaluated include those at or near record efficiencies and those made with new processing strategies. A second area of emphasis, the role of impurities, has focused on sodium in CIS. Cells made with varying amounts of sodium added during CIS deposition were fabricated at NREL using four types of substrates. Best performance was achieved with 0.01 to 0.1 at% sodium. The third area of study has been small-spot measurement of micro-nonuniformities. A new facility was built to focus a laser beam onto a solar cell with 1-um beam size, 1-um resolution and repeatability, and one-sun intensity. Specific projects to date have focused on CdTe and have included the local effect of CdCl2, local intermixing of sulfur, and the effect of temperature-induced stress. Documentation of cell changes at elevated temperatures has been the fourth area of study. Changes seen in CdTe J-V curves are almost certainly related to diffusion of copper from the back contact, but in most cases an activation-energy model predicts sufficient stability for a 30-year product lifetime. Transients seen in some CIS cells are primarily seen in fill-factor and are primarily driven by voltage bias rather than illumination condition. The final area of emphasis has been numerical simulations of CdTe and CI(G)S cells. Results with CdTe are able to replicate experimental data, have explained the effects of partial overlap of the primary junction with the back contact, and have shown how variations in carrier density, carrier lifetime, and CdTe layer thickness impact cell performance.

• Research Organization: National Renewable Energy Lab. (NREL), Golden, CO (United States)
• Sponsoring Organization: US Department of Energy (US)
• DOE Contract Number: AC36-99-GO10337
• OSTI ID: 15000241
• Report Number(s): NREL/SR-520-31458; XAK-8-17619-07; TRN: US200325%%183
• Resource Relation: Other Information: PBD: 1 Jan 2002; Related Information: Work performed by Colorado State University, Fort Collins, Colorado.
• Country of Publication: United States
• Language: English

Related Subjects

14 SOLAR ENERGY
ACTIVATION ENERGY
CARRIER DENSITY
CARRIER LIFETIME
COPPER
ILLUMINANCE
IMPURITIES
PHYSICS
PROCESSING
SODIUM
SOLAR CELLS
STABILITY
SUBSTRATES
SULFUR
THICKNESS
PV
CDTE
CIGS
WHOLE-CELL LOSS ANALYSIS
IMPURITY EFFECTS
SPATIAL MICRO-NONUNIFORMITIES
ELEVATED-TEMPERATURE EFFECTS
COMPUTATIONAL MODELING
SOLAR ENERGY - PHOTOVOLTAICS