Flexible and light weight substrates for Cu(In,Ga)Se/sub 2/ solar cells and modules

The authors report on the fabrication and characterization of ZnO/CdS/Cu(In,Ga)Se/sub 2/ solar cells on flexible metal and polymer substrates. Na for the absorber was provided by NaF precursor films deposited prior to CIGS co-evaporation. The optimum precursor layer thickness was about 30 /spl Aring/ and 100-200 /spl Aring/ for CIGS on polymer and metal substrates, respectively. In comparison with reference CIGS solar cells on soda lime glass substrates mainly the open circuit voltage on flexible foil substrates is decreased. This is explained by insufficient Na content of the CIGS layers and diffusion of substrate constituent elements into the absorber. Secondary ion mass spectrometry of solar cells on Fe/Ni alloy substrates shows impurities of Fe, Ni and Co inside the absorbers. An increased density of deep defects was identified in these solar cells by admittance spectrometry. CIGS solar module fabrication have been demonstrated on enamel coated steel substrates as well as on thin insulated (125 /spl mu/m) ferritic steel foils.