Properties of Polaron Pairs in Conjugated Polymers Studied by Two-Correlated-Pulses Technique(Condensed Matter : Electronic Structure, Electrical, Magnetic and Optical Properties)

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Picosecond time-resolved measurements utilizing a two-correlated-pulses technique have been applied for studying the temperature and electrical field strength dependences of second-order process responsible for the formation of free charge in poly(3-octylthiophene) (PAT) and poly[2-methoxy-5-(2-ethylhexyloxy)-l,4-phenylene-vinylene] (MEH-PPV). We have observed maximum photocurrent at the superposition of pulses (Δt = 0), which originates from the formation of free charge carriers in the second-order process, and it was clarified that fast and delayed components of the lifetime of polaron pairs exist. The lifetime of thermalized or trapped polaron pairs (τ_<delay>) was shown to increase at low temperature and low electrical field strength. The fast-decaying component of a polaron pair with the lifetime τ_<fast> of about 10 ps, which is prescribed to pretrapped polaron pairs, is insensitive to temperature and electrical field strength changes. Polaron pairs with short intercharge distances became remarkable at low temperature and high electrical field strength. For photoluminescence intensity, we obtained the opposite property : quenching of the photoluminescence intensity was maximal at the superposition of the pulses (Δt = 0). We clarified that exciton dissociation hardly contributed to second-order photocurrent.
社団法人日本物理学会の論文
2004-07-15