FREQUENCY-RESPONSE OF MOLECULARLY THIN ALTERNATING-CURRENT LIGHT-EMITTING-DIODES

The frequency response of molecularly thin alternating-current polymer ic light-emitting diodes has been studied. Langmuir-Blodgett (LB) film s of poly(3-hexylthiophene) (PHT) were used as the active emitting mat erial and the device was formed by sandwiching PHT films between LB fi lms of emeraldine base polyaniline. As a step towards molecular electr onic devices, we have shown that even two molecular layers of PHT (app roximate to 6 nm) are sufficient for light emission. The high frequenc y operation limit of the device has been discussed in terms of a charg e accumulation process at the polymer-polymer interface. The electrolu minescence (EL) spectra of different structures have been compared wit h corresponding photoluminescence spectra. A significant blueshift in EL has been observed in thinner structures and its origin has been dis cussed. (C) 1998 American Institute of Physics. [S0021-8979(98)02103-3 ].