PHOTOCONDUCTION IN SOLID FILMS OF C-60

Photoconduction in solid films of C-60 has been investigated as a func tion of applied field, excitation wavelength and light intensity. Expo sure of the films to ultraviolet and visible light (200-800 nm), and e xternally applied voltage produced photocurrent in the range 10(-11)-1 0(-6) A/cm(2); the magnitude depended on the polarity of the illuminat ed electrode. This asymmetry is a function of electric field and light penetration depth. It is attributed to a combined effect of varying e xcitonic electron injection from the Al cathode and a difference in mo bility of holes and electrons. Spectral features of the photocurrent v ary from sample to sample, but a notable number of recurrent bands can be distinguished, in addition to principal features such as their ant ibatic behaviour with the absorption spectrum and higher photogenerati on 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 forb idden electron transitions identified in high-resolution absorption sp ectra of C-60. Correspondingly, a complex relationship between photocu rrent and light intensity is observed.