Mechanical Flexibility of ZnSnO/Ag/ZnSnO Films Grown by Roll-to-Roll Sputtering for Flexible Organic Photovoltaics

The mechanical flexibility of ZnSnO (ZTO)/Ag/ZTO multilayer films prepared on flexible poly(ethylene terephthalate) (PET) substrates by roll-toroll (R2R) sputtering was investigated for use in cost-efficient flexible organic solar cells (FOSCs). The change of resistance (Delta R) of the ZTO/Ag/ ZTO films was measured by means of lab-made outer/inner bending, twist bending, and stretching test systems. The failure bending radii of the ZTO/Ag/ZTO film in the outer and inner bending tests were 3 and 4.5 mm, respectively. In addition, the twisting test showed that the resistance of the ZTO/Ag/ZTO multilayer began to increase at an angle of 38 degrees. Furthermore, the stretching test showed that the strain failure of the ZTO/Ag/ ZTO multilayer film was 3%. The superior flexibility of the ZTO/Ag/ZTO films is attributed to the existence of a ductile Ag layer and the mechanical stability of the amorphous ZTO film. Similar performances of the FOSCs with flexible ZTO/Ag/ZTO anodes to reference OSCs with ITO anodes indicate that the R2R sputter-grown ZTO/Ag/ZTO multilayer is promising as an indium-free flexible anode for cost-efficient FOSCs. (C) 2012 The Japan Society of Applied Physics