A photophysical study of PCBM thin films

Abstract

The photophysical properties of [6,6]-phenyl C 61 butyric acid methyl ester (PCBM) are found to differ depending on its concentration in thin films. A film of dispersed PCBM molecules in polystyrene (PS) showed only weak absorption in the visible region (400–700 nm) with a single S 1 → S 0 emission band at around 700 nm. By comparison, a film of pristine PCBM showed heightened absorption in the visible region and the presence of an additional higher energy emission at ∼500 nm assigned to the presence of charge transfer (CT) transitions in crystalline PCBM. The energy of the CT exciton is estimated to be ∼2.8 eV.