Utility of Thin-Film Solar Cells on Flexible Substrates for Space Power

ABSTRACT The thin-film solar cell program at NASA GRCis developing solar cell technologies for spaceapplications which address two critical metrics:specific power (power per unit mass) and launchstowed volume. To be competitive for many spaceapplications, an array using thin film solar cells mustsignificantly increase specific power while reducingstowed volume when compared to the presentbaseline technology utilizing crystalline solar cells.The NASA GRC program is developing twoapproaches. Since the vast majority of the mass of athin film solar cell is in the substrate, a thin film solarcell on a very lightweight flexible substrate (polymeror metal films) is being developed as the firstapproach. The second approach is the developmentof multijunction thin film solar cells. Total cellefficiency can be increased by stacking multiple cellshaving bandgaps tuned to convert the spectrumpassing through the upper cells to the lower cells.Once developed, the two approaches will be mergedto yield a multijunction, thin film solar cell on a verylightweight, flexible substrate. The ultimate utility ofsuch solar cells in space require the development ofmonolithic interconnections, lightweight arraystructures, and ultra-lightweight support anddeployment techniques.