Roll-to-roll sputtered Si-doped In₂O₃/Ag/Si-doped In₂O₃ multilayer as flexible and transparent anodes for flexible organic solar cells

Amorphous Si-doped In₂O₃ (a-ISO), crystalline Ag, and a-ISO layers were sputtered onto a flexible polyethylene terephthalate substrate by using a lab-scale roll-to-roll (RTR) sputtering system. The resulting a-ISO/Ag/a-ISO multilayer was studied to optimize their characteristics for use as flexible and transparent anodes in flexible organic solar cells (FOSCs). To optimize the electrical and optical properties of the a-ISO/Ag/a-ISO multilayer, the thicknesses of each a-ISO and Ag layer were varied by controlling the DC power applied on ISO and Ag targets during the RTR sputtering process. Compared to the top and bottom a-ISO layer, controlling the thickness of the Ag layer is more effective for realizing a low sheet resistance and high transmittance a-ISO/Ag/a-ISO multilayer. At optimized thicknesses of a-ISO (30nm) and Ag (10nm), a symmetric a-ISO/Ag/a-ISO multilayer showed a sheet resistance of 5.256 Ω/sq and a high optical transmittance of 83.9%. Various bending test results showed that the high failure strain of the Ag interlayer led to good flexibility of the multilayer films. Furthermore, the authors discuss the effect of each a-ISO and Ag layer thickness on the performance of FOSCs fabricated on RTR-sputtered a-ISO/Ag/a-ISO anodes.