CHARGE-TRANSFER PROCESSES IN BUCKMINSTERFULLERENE FILMS

The spectral dependence of the photogeneration efficiency eta in sublimed undoped C60-C70 films has been determined from photoinduced xerographic discharge curves. The dependence of eta on the exciting light wavelength from 7250 to 3500 angstrom and electric field are reported. At an applied field of 2.7 x 10(5) V cm-1, eta is essentially wavelength independent with a value of about 5 x 10(-3) from 7250 to 5500 angstrom. At shorter wavelengths, eta is essentially proportional to the absorption coefficient, rising by more than an order of magnitude to about 6 x 10(-2) at 3500 angstrom. The difference between the charge-transfer efficiencies of these two regions is discussed in terms of an Onsager surface-mediated dissociation of singlet excitons.