NEW PRINCIPLE OF THE MOLECULAR PHOTO-FET

Irena Kratochvílová

Institute of Physics, Academy of Sciences of the Czech Republic, Na Slovance, Prague, Czech Republic

We report a possibility of a reversible formation of charge carrier traps in molecular system consisting of polymer matrix containing photochromic species. One can envisage a construction of photo-FET device in which source-drain current in a semiconductor film is influenced by photo formed dipolar fields associated with charge carrier traps in a photoactive “gate” layer. The results demonstrate that the suitable photochromic reaction can modulate the transport of the charge carriers in a semiconducting film between the source and drain electrodes. The speed of the modulation is limited by the speed of the photochromic transformation – in a suitable system with a free volume of the polymer it can reach microseconds scale. The speed can be improved using the polarity of the exciting state where picoseconds scale can simply be reached. The experimental effects presented here, leading to the decrease of charge carrier mobility and therefore of the photocurrent by factor ca. 3, strongly depends on the sample geometry, thicknesses of the films and the concentration and orientation if photochromic additive in the “gate” polymer layer.The finding of the suitable parameters is in progress. DFT calculations on model dimer (H₂Pc)₂ show changes in electronic structure caused the induced dipole which lower the carrier mobility.