NEAR-INFRARED ELECTROCHROMISM IN LIXC60 FILMS

Fullerene thin films deposited on transparent substrates were found to exhibit electrochromic switching in the near infrared. The as-deposited films were optically transparent between 0.9 and 2.0 mum. The oxidation state of the fullerene films was altered by electrochemical insertion of Li ions from a liquid electrolyte. Upon Li insertion the transmittance of the films decreased markedly in the near infrared. Subsequent Li extraction restored most of the original transparency. The observed electrochromism occurs due to switching between the C60 and C-60(1-) oxidation states. Electrochemically, the insertion process is highly reversible. The lack of complete optical reversibility is attributed to solubility of C-60(1-) in the electrolyte employed.