Poster: "Charging and discharging of single F8BT nanoclusters in hole injection devices"

PALACIOS, RODRIGO E.; RIVAL, ARNAUD; ADACHI, TAKUJI; BARBARA, PAUL F.

New Orleans, Louisiana, USA

Congreso; The 235th American Chemical Society National Meeting; 2008

The American Chemical Society

Detailed understanding of polaron charging/discharging processes in conjugated polymers (CPs) is crucial for the application of these materials in organic electronic devices. The study of these processes is usually carried out in complete devices creating difficulties due to the large number of polaron related process occurring in a functional device. Additionally, the disordered nature of CPs at the nanoscale further complicates these studies. In order to reduce these complications we studied hole-polaron charging/discharging processes on individual F8BT nanoclusters in simple hole-only capacitor-like devices using Fluorescence Voltage Single Molecule Spectroscopy (F-V/SMS). The technique is based on the quenching or decay of singlet excitons induced by hole-polarons which leads to a decrease of conjugated polymer florescence intensity. F-V/SMS uses this relationship between charges and fluorescence to indirectly measure electrical charges in individual particles. Two types of devices were studied having either a single layer PEDOT:PSS or a bilayer TPD/CBP as the hole injection film. In both types of devices the nanoclusters charging behavior was dependent on the magnitude of the applied bias resembling the charging behavior of typical semiconductor capacitors. At values of bias below the threshold voltage, charge injection into the particles was not observed; whereas at higher values, charge injection increased semi-linearly with increasing bias. Additionally, charge injection was found to be dependent on the optical excitation intensity in PEDOT devices but not in TPD/CBP devices. These results indicate that photo-assisted hole-injection is the prevailing injection mechanism in PEDOT devices whereas thermionic injection is the dominant mechanism in TPD/CBP devices. Finally, a slow recovery of the fluorescence intensity (after a bias induced quenching) was observed in both devices. This slow florescence recovery was associated with the formation of deep trapped holes during hole-charging of the CP nanoclusters.