Photoeffect in Metal‐Free Phthalocyanine Crystals

Abstract

AbstractThe drift mobilities of electrons (0.43 to 0.70 cm2 V−1s−1) and holes (0.24 to 0.56 cm2 V−1s−1) in thoroughly purified metal‐free phthalocyanine crystals have been measured by illumination with short light pulses. The mobilities of carriers of both sign diminish with increasing temperature: μ ∽ T−n, n = 1.3 to 1.5 for holes, n = 1.5 to 1.9 for electrons. The quantum yields of holes and electrons are equal in magnitude (7 ± 6 × 10−5 at 295 °K) and increase exponentially with temperature. Probably, the generation of photocarriers is caused by thermal dissociation of singlet excitons. The difference between the energy gap and the singlet exciton energy is equal to the activation energy of quantum yield (0.19 cV). Under the giant ruby laser pulse the photocurrent in pure crystals is a linear function of light intensity, whereas in crystals containing impurities the square dependence is observed. The mechanism of charge carrier production under high light intensity is probably the singlet exciton annihilation, the rate constant being 4 × 10−15 to 8 × 10−14 cm3s−1.