Photogeneration and charge transport mechanisms in thin films of organic electron acceptor 2,4,7-trinitro-9-fluorenone

The photogeneration process in thin films of vacuum-evaporated amorphous 2,4,7-trinitro-9-fluorenone (a-TNF) is investigated by steady-state photoconductivity measurements and by the photoinduced discharge method. It was found that in the intrinsic spectral range of absorption (λ≤400 nm) the charge carrier photogeneration mechanism includes several steps. The final step, thermal dissociation of light generated electron-hole pairs, is realized according to the Onsager mechanism. The effect of trapping centers on the conductivity of thin films of a-TNF is investigated by space charge limited current (SCLC), steady-state photoconductivity, and transient photoconductivity methods. It is suggested that the transport of charge carriers in a-TNF is controlled by traps.