Mechanical integrity of flexible Ag nanowire network electrodes coated on colorless PI substrates for flexible organic solar cells

We investigated the mechanical integrity and flexibility of the transparent Ag nanowire (NW) network electrode coated on colorless polyimide (CPI) substrates using a lab-made bending test apparatus involving detailed outer/inner bending, twisting, and stretching for flexible organic solar cells. At the optimized conditions with a coverage rate of 42.25%, the Ag NW network electrode showed a sheet resistance of 21.76 Ω/□ and an optical transmittance of 84.84%, which are better than the values obtained from a conventional flexible amorphous ITO film. Notably, the Ag NW electrode had a constant resistance change (ΔR/R0) within an outer and inner bending radius of 5 mm each. The twisting test also revealed that the resistance of the Ag NW network electrode remained constant below a twisting angle of 35° due to the superior flexibility of the Ag NW network. Furthermore, the stretched Ag NW electrode showed a fairly constant resistance change (ΔR/R0) up to 4%, which is more stable than the resistance change of a flexible ITO electrode. Flexible organic solar cells were fabricated on flexible Ag NW network electrodes and peeled off the supporting glass substrates. The power conversion efficiency of the flexible solar cells was measured to be 2.62%, demonstrating the possibility of Ag NW networks as flexible transparent conducting electrodes for flexible organic solar cells.