1 Results In this contribution we deal with photophysical and photoelectrical study of novel fluorene-thiophene copolymers, and thiophene-based oligomers and polymers, the syntheses of which are reported in our other contributions. Information about electronic structure of the polymers was obtained from cyclic voltammetry and absorption spectroscopy. The absorption of the polymers under study covers the whole visible region; the low band-gap polymer (Eg=1.35 eV) exhibited the long-wavelength absorption maximum at 785 nm with a shoulder up to 950 nm in thin layer. The ionization potential, EIP (HOMO level) in the range 4.85-5.35 eV and electron affinity, EA (LUMO level) 2.8-3.8 eV for the polymers under study were estimated; hence, polymers with donor as well with acceptor character were used. Photoluminescence, charge photogeneration and transport properties were investigated. The performance could be improved by polymer blending or doping. Photoinduced electron transfer between donor and acceptor molecules with significantly different HOMO/LUMO levels (formation of bulk heterojunction) can efficiently dissociate photogenerated excitons. Fluorescence quenching after blending or acceptor doping was demonstrated and also an increase in photostability, which was followed by absorption spectroscopy, was observed. In addition, the surface photovoltage method was utilized for photophysical study of thin films and evaluation of the thickness of the space charge region and the diffusion lengths by fitting theory to the experimental data. The results are discussed also in relation to photoluminescence study of thin films. 1 Results In this contribution we deal with photophysical and photoelectrical study of novel fluorene-thiophene copolymers, and thiophene-based oligomers and polymers, the syntheses of which are reported in our other contributions. Information about electronic structure of the polymers was obtained from cyclic voltammetry the absorption of the polymers under study covers the whole visible region; the low band-gap polymer (Eg = 1.35 eV) exhibits the long-wavelength absorption maximum at 785 nm with a shoulder up to 950 nm in thin layer. The ionization potential, EIP (HOMO level) in the range 4.85-5.35 eV and electron affinity, EA (LUMO level) 2.8-3.8 eV for the polymers under study were estimated; hence, polymers with donor as well with acceptor character were used. Photoluminescence, charge photogeneration and transport properties were investigated. The performance could be improved by polymer blending or doping. Photoinduced electron transfer between donor and acceptor molecules with significantly different HOMO / LUMO levels (formation of bulk heterojunction) can efficiently dissociate photogenerated excitons. Fluorescence quenching after blending or acceptor doping was demonstrated and also an increase in photostability, which was followed by absorption spectroscopy, was observed. , the surface photovoltage method was utilized for photophysical study of thin films and evaluation of the thickness of the space charge region and the diffusion lengths by fitting theory to the experimental data. The results are discussed also in photoluminescence study of thin films.