Mechanical integrity of flexible InZnO/Ag/InZnO multilayer electrodes grown by continuous roll-to-roll sputtering

The mechanical integrity of a flexible ZnO-doped In2O3 (IZO)/Ag/IZO multilayer electrode deposited onto a flexible PET substrate using a continuous roll-to-roll (R2R) sputtering system was investigated by means of outer/inner bending, twisting and stretching tests. The R2R-sputtered flexible IZO (40 nm)/Ag (12 nm)/IZO (40 nm) electrode with a sheet resistance of 5.37 Ω/sq and an optical transmittance of 87.3% exhibited superior flexibility due to existence of a ductile Ag layer with high strain failure. It was noteworthy that the failure bending radius (5.5 mm) of the inner bending test was lower than that (6.5 mm) of the outer bending test due to complete separation of the cracks on the top IZO layer during the outer bending test. In addition, the twisting test showed that the resistance of the flexible IZO/Ag/IZO electrode began to increase at an angle of 26°. Furthermore the stretching test demonstrated that the strain failure of the IZO/Ag/IZO multilayer was 2.4%, which is higher than those of conventional flexible ITO electrodes. The mechanical integrity of the R2R-sputtered IZO/Ag/IZO multilayer indicated that hybridization of an oxide and Ag metal is a promising flexible electrode scheme for next generation flexible organic solar cells.