Spectral and photocarrier dynamics in thin films of pristine and alkali-doped C 60

Abstract

This article summarizes our contribution to three distinct areas of research on thin films of fullerenes. In the first part we present results of an in-situ optical absorption study on K-doped thin films of C 60 from which an unambiguous assignment of certain low energy electronic transitions in C 60 and K x C 60 was deduced. The second part of the article concerns transient and steady-state photoconductivity (PC) of pristine and oxygen-exposed thin films of C 60 examined as a function of temperature and photon energy. We find that the presence of oxygen is responsible for the creation of deep traps which reduce the steady-state and transient PC by several orders of magnitude, particularly in the 1.6–2.3 eV excitation region. The thermally activated transport in an oxygen-free C 60 sample is quenched upon exposure to oxygen so that both steady-state and transient PC become nearly temperature independent. In the last part we present two examples of utilizing C 60 thin films for application in opto-electronics. The mechanism of light-induced charge transfer at the conducting polymer-C 60 interface is described and the current versus voltage rectifying characteristics (> 10 4) of the MEH-PPV C 60 thin film heterojunction is presented. In addition, a non-linear transient photovoltaic response in a AlC 60 Au sandwich-type device featuring control of polarity with optical bias is described.