Relaxation of excited states and analysis of photoconductivity spectrum of C/sub 60/ polycrystalline films

Summary form only given. Relaxation of excited states as well as photocarrier generation and transport in C/sub 60/ polycrystalline films have been investigated by means of luminescence and steady-state photoconductivity. A tentative explanation of the relaxation of excited states and photocarrier generation in C/sub 60/ polycrystalline film has been developed, based on the following results. On one hand the shape of the luminescence emission spectrum is independent of the excitation energy (/spl lambda//sub exc/=330, 400, 550, 610, 640nm in the range (/spl lambda//sub em/=700-850nm). This result indicates that internal conversion takes place to the lowest localized electronic state. The maximum of the luminescence emission corresponds to 730nm (1.7eV). On the other hand the temperature dependence of the photoconductivity shows that the activation energy is constant Ea(/spl sigma/ph)=0.2eV for (/spl lambda//sub exc/=300 and 600nm. Carriers might be generated from the lowest excited state of Frenkel-type exciton carrying a substantial charge transfer character. In addition subsequent transport of carriers might happen in narrow conduction states by hopping from site to site (the conduction state has been estimated at 1.9eV). The steady-state photoconductivity action spectrum has been analyzed in term of the bimolecular recombination model [1]. This model shows that the photocarrier generation efficiency () is almost constant in the wavelength range 300/spl les//spl lambda//spl les/620nm. Moreover, the thickness dependence of the photoconductivity action spectrum can be also explained. Bimolecular recombination appears to be the most efficient process that shortens the free carrier life time.