The opticd limiting action of CSU in toluene solution is mainly due to revem saturable absorption (RSA). It is shown that the formalism describing nonlinear optical response due to instantaneous two-photon absorption can be used in the case of sequential two-photon absorption, yielding effective values of the relevant parameters of optical nonlinearity due to RSA. The effective twc-photon absorption parameter and the effective nonlinear refractive index parameter y&, which are related respectively to the imaginary and real parts of the effective third-order susceptibility $2. were measured by the L-scan technique as a function of fullerene concentration and of incident laser intensity and wavelength over the 42W nm region. The concentration dependence of these parameters indicates that the solution is optically lhin as far as the ground state of Cm is concerned, whereas he wavelength dependence confirms the applicability of the formalism used in the sequential two-photon absorption model. Comparisons are made with other I-scan results on Cm.

We present a systematic study of the effects of post-fabrication annealing on the performance of photovoltaic devices that incorporate a photoactive donor–acceptor dispersed heterojunction system. Solar cells have been fabricated based on poly(3-octylthiophene) as donor (D) and single-wall carbon nanotubes as the electron acceptor (A) with a PEDOT:PSS hole transport layer. A post-fabrication annealing treatment was carried out at a temperature range of 40–200 °C. The best results were obtained at 120 °C; at this temperature the cell shows a short circuit current, Isc = 0.5 mA cm−2, an open circuit voltage, Voc = 0.75 V and a fill factor, FF = 0.6, resulting in a power conversion efficiency of η = 0.22% under AM 1.5 (100 mW cm−2) white light illumination. The annealing treatment led to a doubling of the power conversion efficiency. This was attributed to a better charge carrier transport in the polymer matrix and more effective charge separation and collection.

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