Atmospheric Pressure Chemical Vapor Deposition and Jet Vapor Deposition of CdTe for High Efficiency Thin Film PV Devices: Final Technical Report, 26 January 2000 - 15 August 2002

ITN's three-year project, Atmospheric Pressure Chemical Vapor Deposition (APCVD) of CdTe for High Efficiency Thin Film PV Devices, had the overall objectives of improving thin-film CdTe PV manufacturing technology and increasing CdTe PV device power-conversion efficiency. CdTe deposition by APCVD employs the same reaction chemistry as has been used to deposit 16%-efficient CdTe PV films, i.e.,close-spaced sublimation, but employs forced convection rather than diffusion as a mechanism of mass transport. Tasks of the APCVD program center on demonstration of APCVD of CdTe films, discovery of fundamental mass-transport parameters, application of established engineering principles to the deposition of CdTe films, and verification of reactor design principles that could be used to designhigh-throughput, high-yield manufacturing equipment. Additional tasks relate to improved device measurement and characterization procedures that can lead to a more fundamental understanding of CdTe PV device operation, and ultimately, to higher device conversion efficiency and greater stability. Under the APCVD program, device analysis goes beyond conventional one-dimensional devicecharacterization and analysis toward two-dimensional measurements and modeling. Accomplishments of the concluding year and extension of the APCVD subcontract included: incorporation of high-resistivity transparent buffer layers and achievement of 12.3%-efficient (NREL-measured, but not certified) devices by APCVD; analysis of scale-up issues related to APCVD, analysis of dust formation dynamics;demonstration of the inherent deficiencies of APCVD for CdTe manufacturing; modeling effects of CdSTe and SnOx layers; and electrical modeling of grain boundaries; design and construction of a low-pressure jet vapor deposition (JVD) reactor; JVD CdTe film characterization as a function of substrate and source temperature; demonstration of high growth rates using JVD; and superstrate-type andsubstrate-type device fabrication using low-substrate-temperature JVD CdTe films.