Semiconductors group

Abstract:

A study is presented on how encapsulation of conjugated polymer chains affects the motion of photoexcitations and the formation of interchain aggregates in solid films. It is shown that threading of a poly(diphenylene vinylene) backbone inside insulating cyclodextrins (rotaxination) and/or complexation of the chains with poly(ethylene oxide) are effective means of preventing the diffusion of excitons to nonradiative defect sites. Ultrafast time-resolved photoluminescence data reveal that excitation transfer between encapsulated chains is still possible and, for the case of rotaxination, is likely to be facilitated through close packing of end groups belonging to adjacent chains. © 2006 American Institute of Physics.

Abstract:

We have used differential terahertz spectroscopy to monitor performance degradation in state-of-the-art polymer field effect transistors (pFETs) based on poly[(9,9-dioetylfluorene-2,7-diyl)-co-(bithiophene)] (F8T2). After extended periods of operation holes are trapped in the polymer, increasing the device's threshold voltage. We monitor the trapped charge density using THz spectroscopy, and investigate the device's recovery as trapped holes are thermally removed. Illuminating the devices for a period with above-bandgap photons leads to a change in the terahertz transmission through the device, which is short lived after switching the light off.