Slope to intercept ratio of low-field photogeneration efficiency in β-metal-free phthalocyanine

Using the delayed collection field technique we measured the slope to intercept ratio of the photogeneration quantum efficiency in β-metal-free phthalocyanine. At short delay times between pulsed laser illumination and the application of the collection field slope to intercept ratio is significantly smaller than the value predicted by the Onsager theory of geminate recombination. At longer delay times, exceeding about 200 ms, the slope to intercept ratio reaches the theoretical value indicating that the time evolution of geminate recombination is significantly slowed down by traps. At higher fields the carrier generation is dominated by the field modulated yield of the geminate pairs.