Spectral and Photocarrier Dynamics in Thin-Films of Pristine and Alkali-Doped C60

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 C60 from which an unambiguous assignment of certain low energy electronic transitions in C60 and KxC60 was deduced. The second part of the article concerns transient and steady-state photoconductivity (PC) of pristine and oxygen-exposed thin films of C60 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 C60 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 C60 thin films for application in opto-electronics. The mechanism of light-induced charge transfer at the conducting polymer-C60 interface is described and the current versus voltage rectifying characteristics (> 104) of the MEH-PPV/C60 thin film heterojunction is presented. In addition, a non-linear transient photovoltaic response in a AlC60/Au sandwich-type device featuring control of polarity with optical bias is described.