| The problems of energy crisis and global warming make every government to promote the research of alternative energy. Solar energy is one of the most important alternative energy. Over the past decades, the polymer solar cell has drawn a great deal of interst compared with the inorganic solar cell due to lots of advantages, such as flexibility, low cost, light weight, and an easy fabrication process. However, the energy conversion efficiency for polymer solar cell is still lower compared with commencial solar cell till now, because of the low charge collection and charge transition. There are two mainly methods to solve such problem which fabricate new polymer donor to adsorb in vis-red spectra and prepare the well ordered donor-acceptor active layer.Preparation of polymer photoactive layer in bulk heterojunction organic photovoltaic (OPV) has attracted much attention. Former research showed that highly ordered polymer (donor)/PCBM derivatives (acceptor) blends are expected, because in such layer exciton can almost totally convert to free charges, electrons and hole are able to transport in different phase. In this thesis, a new procedure and method is proposed for the fabrication of highly ordered photoactive layer by grafting donor polymer poly(9,9-dioctylfluorene-2,7-di-2-thiophenyl)(PFO-Th) onto indium tin oxide electrode surface. PFO-Th is known a good donor material due to its low bandgap and well absorption in vis-red spectra.The grafting of ordered donor polymer brushes onto ITO surface would be interesting alternative, possibly helping charge injection and charge transport processes for solar cell due to the donor polymer directly bounded onto the anodic electrode surface with chemical bond. The polymer brushes will be fabricated by "grafting from" methods. Specific content as follows:(1) Synthesis of the monomer:2,7-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-9,9-dioctylfluorene,9,9-dioctylfluorene-2,7-bis(trimethylborate),2,5-dibromothiophene and (4-Bromobenzyl)phosphonic acid were successfully synthesized and characterized by FT-IR and1H NMR.(2) To form the initiator monolayer, initiator (4-Bromobenzyl phosphonic acid) was adsorbed on the surface of indium-tin oxide (ITO) by self-assembly technique. The adsorption behavior was studied by contact angle measurement. By optimizing the adsorption condition, such as adsorption time and contration of initiator, the best adsorption condition was obtained, which is15mM initiator concentration and12h adsorption time.(3) The preparation of polymer film:Under the presence of catalyst,2,5-dibromothiophene and2,7-Bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-9,9-dioctylfluorene were surface polymerized on the surface of initiator modified ITO by Suzuki polycondensation reaction. Several analytical techniques such as contact angle measurement, UV-VIR, scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), photoluminancence and votage-current measurement were employed to characterize the PFO-Th polymer on substrates. The polymerization conditions were investigated. SEM and AFM images showed that the morphology of polymer film is look like cauliflower, which exsiting holes between particles. The ordering of polymer layer was studied by XRD and showed that both of long polymerization time and high monomer concentration increased the long-range order of polymer film. After different annealing treatment, XRD results revealed that with the increasing of the annealing temperature, the long-range order of polymer film was disappeared. In addition, cyclic voltammetry (CV) measurement was employed to study electrochemical performance of polymer film, the CV results showed that the bandgap of polymer film was influcened by the polymerization time and monomer concentration. The electrical property was studied by current-voltage (Ⅰ-Ⅴ). I-V result revealed that the contact between polymer film and ITO was ohmic contact. |
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