Stable Charge-Transfer Doping of Transparent Single-Walled Carbon Nanotube Films

Single walled carbon nanotube (SWCNT) films are candidates for use as transparent electrodes, especially where low-cost, flexible materials are desired. Chemical doping is a critical step in fabricating conductive films as doping substantially decreases the sheet resistance within SWCNTs and at tube−tube junctions. Despite the importance of chemical doping, surprisingly little effort is devoted to developing doping chemistry. Concentrated acid solutions are typically used to dope SWCNT films. Although they are effective at reducing the sheet resistance of SWCNT films, this method is plagued by two critical drawbacks. The first is that concentrated acid baths, such as HNO 3, are extremely harsh and will damage virtually any device technology. Second, the film resistance is unstable and rises dramatically over time. These drawbacks make implementation of SWCNT transparent, conducting films in technological applications extremely difficult. Here, we report an alternative doping scheme that utilizes a single-electron oxidant (triethyloxonium hexachloroantimonate) to effectively dope the SWCNT films. As evidenced by optical and electrical measurements, the compound effectively p-dopes SWCNT films. In addition to the effective doping, the resultant film resistance is stable over time. The films doped with triethyloxonium hexachloroantimonate outperform nitric acid doped films by a factor of 2.5 over time. This study introduces a new category of chemical dopants that yield stable, transparent, and conductive SWCNT films suitable for technological applications.