Transparent and ultra-flexible PEDOT:PSS/ITO/Ag/ITO on Parylene thin films with tunable properties

Transparent and flexible conductive materials are critical components in many optoelectronic devices, such as wearable electronics, biosensors, displays, etc. Conventional transparent electrodes made of a single material, such as indium tin oxide (ITO), ultrathin metals, graphene and poly-(3, 4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT:PSS) have limitations and hardly possess the desired combination of broadband transmittance, low electrical resistivity, mechanical flexibility, and biocompatibility. Herein, we designed and constructed an ultra-flexible, conductive, transparent thin film using a PEDOT:PSS/ITO/Ag/ITO multilayer structure on Parylene C. The multilayer assembly was optimized to achieve the lowest theoretical reflectance by simulating the coatings admittance loci under the preferred reference wavelength. ITO and Ag were deposited consecutively using RF magnetron sputtering at room temperature, followed by spin-coating of PEDOT:PSS. The sputtering deposition temperatures were tuned to achieve the optimal optical and electrical properties. Compared to a single-layer ITO film of equivalent thickness, the multilayer films exhibited significantly decreased sheet resistance, reduced electrochemical impedance, remarkable transmittance, large Young's modulus values, and superior stability in air and saline. The multilayer films also showed strong adhesion to the Parylene C substrate and subsequently excellent bending tolerance. Moreover, the peak transmittance of our multilayer flexible thin films could be tailored to a specific wavelength for particular applications, such as optogenetics that utilizes light of different wavelengths to excite or inhibit the activity of genetically targeted neurons or intracellular signaling pathways.