Dispersive electron transport in an electroluminescent polyfluorene copolymer measured by the current integration time-of-flight method

Campbell, Alasdair J.; Bradley, Donal D. C.; Antoniadis, Homer
October 2001
Applied Physics Letters;10/1/2001, Vol. 79 Issue 14, p2133
Academic Journal
Here, we report results of both traditional current mode and current integration mode time-of-flight (TOF) measurements on the electroluminescent polyfluorene copolymer poly(9,9-dioctylfluorene-co-benzothiadiazole) (BT). Current mode TOF shows a strong but dispersive electron transport signal. The mobility derived from the current integration mode transit time (t[sub Q]) increases with decreasing film thickness as expected for dispersive transport. The fastest carriers in the photogenerated carrier packet are estimated to have mobilities of order 10[sup -3] cm[sup 2]/V s at applied fields of 0.5 MV/cm. Holes are heavily trapped close to the interface at which they are photogenerated. The TOF signals decay with repeated measurement and t[sub Q] remains constant with applied field. The transport properties of BT are thus in complete contrast to those of other polyfluorenes which show high-mobility nondispersive hole transport but weak and highly dispersive electron transport. © 2001 American Institute of Physics.


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