Abstract
Jablonski diagram comparing the energy of the intramolecular and the more delocalised charge transfer states in thin films of PCBM.
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.