The wavelength, temperature, time and intensity dependence of photocurrent of metal-free phthalocyanine (H2Pc) and copper phthalocyanine (CuPc) single crystals were investigated. The thermal activation energies in the dark are 0·5 and 0·6 eV for H2Pc and CuPc respectively and the corresponding photo-thermal activation energies are 0·3 and 0·2 eV. An energy level scheme for single crystals of H2Pc and CuPc is proposed which consists of two trapping levels and five narrow optically active valence bands. In H2Pc (CuPc), one trapping level at 0·5 eV (0·6 eV) above the valence band edge to which the charge carriers are thermally excited in the dark; and the other trapping level is at 0·3 eV (0·2 eV) below the conduction band edge where all the optical transitions terminate. In H2Pc(CuPc), the forbidden gap is 1·44 eV (1·34 eV) wide; the five valence bands are at the band edge, and 0·09 (0·22), 0·42 (0·63), 0·69 (0·90), 1·32 (2·17) eV below the band edge.
Volume 43, 2020
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