Study On Well-Ordered Nanoporous Inorganic Thin Films Based On Block Copolymer

The phase behavior of thin films of polystyrene cylinder-forming polystyrene-poly (methyl methacrylate) (PS-b-PMMA) diblock copolymer has been systematically investigated. The thin film with high aspect ratio cylindrical microdomains perpendicular to PG (PS-r-PMMA containing certain mole fraction glycidyl methacrylate) neutral brush modified substrate (ITO) has been obtained by thermal annealing and acetone vapor annealing methods. Then the thin film used as a template was immersed in the titanium dioxide (TiO2) sol that was prepared by sol-gel method. The TiO2 sol would be loaded in PMMA with the swelling of PMMA. The PMMA in PS-b-PMMA thin film was removed by UV and the PS nanopillar thin film was obtained. The zinc oxide (ZnO) sol that was prepared by sol-gel method was poured into the pores of PS nanopillar thin film. Then the above thin films that containing TiO2 and ZnO sol was aged and calcined at high temperature. Finally, the TiO2 and ZnO well-ordered nanoporous thin films were obtained. The PS nanopillar film that obtained by UV etch was modified by CTAB aqueous solution and used as a template. The CdS nano particles were deposited into the pore of PS nanopillars by CBD method, and then the template was calcined after dried and the CdS nanoporous thin film was obtained. The TiO2/P3HT and CdS/P3HT well-ordered bulk heterojunction thin films were prepared by poured the P3HT/dichlorobenzene solution into the pore of TiO2 and CdS thin films. The heterojunction thin film were in a vacuum thermal annealed at 150℃ for 15 min, subsequently～50 nm thickness of Au electrode was prepared by vacuum evaporation method.The morpholoyies of self-assembly block copolymer thin film were investigated by transmission electron microscope (TEM), field-emission scanning electron microscope (FESEM), atomic force microscope (AFM). The results show that the aspect ratio of obtained PS nanopillar thin film is only 3 by thermal annealing, but first thermal annealing again with acetone vapor annealing 30min can obtain the PS nanopillar thin film with aspect ratio of 4.The well-ordered nanoporous semiconductor TiO2, ZnO and CdS thin films were characterized by FESEM, AFM, resistivity, and transmittance test. As a result, the distribution and size of pores in TiO2 and ZnO nanoporous thin films are uniform. The distribution of pores in CdS nanoporous prepared in beaker is loosened and discontinuous. But the distribution of pores in CdS nanoporous thin film prepared in hydrothermal reactor is concentrated and the pores are uniform and continuous. The resistivity of TiO2, ZnO and CdS thin film are 4.24 Ω·cm,4.97 Ω·cm and 3.08Ω·cm, respectively, only 3-5 times higher than ITO glass. The highest light transmittance of the TiO2 thin film is more than 90%, the light transmittance of ZnO and CdS thin film are about 80% and 70%, respectively. The light transmittance of CdS thin film is poorer than TiO2 and ZnO.Finally, the photoelectric conversion efficiency of TiO2/P3HT and CdS/P3HT well-ordered bulk heterojunction solar cells is tested. The photoelectric conversion efficiency of TiO2/P3HT heterojunction solar cell is about 0.04%, and the photoelectric conversion efficiency of CdS/P3HT heterojunction solar cell is reach to 0.06%.