Highly Conductive and Transparent Coatings via Low‐Temperature Hydroiodic Acid Vapor Treatment of Oxo‐Graphene Thin Films

Transparent conductive graphene films are typically fabricated at processing temperatures above 500°C, making the applied processes unsuitable for flexible polymer substrates and limiting their integration into semiconductor device technologies. Here we demonstrate a method for fabricating such films at temperatures below 200°C. To this end, oxo‐graphene flakes are assembled into continuous films using the double self‐assembly technique. Subsequent hydroiodic acid (HI) vapor treatment at 40°C removes the oxygen‐containing groups and, combined with a mild 180°C annealing step on heat‐stable substrates, lowers the sheet resistance by more than a factor of five to about 3 kΩ/sq while preserving optical transparencies of up to 88% at 550 nm wavelength. The trade‐off between sheet resistance and transparency is set by the number of stacked layers, and on flexible polyethylene terephthalate (PET), where the annealing step is precluded, the films reach a sheet resistance of about 2.8 kΩ/sq after the HI step alone. These results demonstrate that the double self‐assembly of oxo‐functionalized graphene flakes, combined with mild HI‐vapor reduction and a 180°C annealing step, can deliver highly transparent and conductive graphene films while remaining compatible with semiconductor device technologies.