Optical measurements (absorption coefficients, photoluminescence) and light-induced electron spin resonance (LESR) technique was used to study on photoinduced charge generation and transfer in conjugated polymer/fullerene composites. The quenching of fluorescence by C₆₀ gives first information on the effective charge transfer from P3DDT to C₆₀. At 77 K two kinds of LESR signal were identified one, from polaron (P⁺) on the polymer chains and anion radical (C₆₀^-) of the fullerene. The large difference of relaxation rates of created radicals were estimated by microwave power saturation studies. Moreover for the first center (P⁺) two contributions to the LESR were observed: a initial one and a photoinduced one. The light power dependence of the last contribution into the P⁺ and C₆₀^- ESR signals is of bimolecular type (I^0.5). Solar cells based on P3DDT/C₆₀ and P3DDT/PCBM are prepared and characterised