Photoconduction in solid films of C-60

Photoconduction in solid films of C-60 has been investigated as a function of applied field, excitation wavelength and light intensity. Exposure of the films to ultraviolet and visible light (200-800 nm), and externally applied voltage produced photocurrent in the range 10(-11)-10(-6) A/cm(2); the magnitude depended on the polarity of the illuminated electrode. This asymmetry is a function of electric field and light penetration depth. It is attributed to a combined effect of varying excitonic electron injection from the Al cathode and a difference in mobility of holes and electrons. Spectral features of the photocurrent vary from sample to sample, but a notable number of recurrent bands can be distinguished, in addition to principal features such as their antibatic behaviour with the absorption spectrum and higher photogeneration yield in the long-wavelength part of the spectra above 400 nm. This behaviour can be explained by a vast range of orbitally and spin forbidden electron transitions identified in high-resolution absorption spectra of C-60. Correspondingly, a complex relationship between photocurrent and light intensity is observed.