| Semiconducting conjugated polymers are a promising candidates for thin film solar cell manufacturing. The advantages of polymer solar cells over traditional silicon photovoltaics include low cost, light weight, and flexibility. Traditional methods for polymer solar cell fabrication are based on solution processing techniques such as spin-coating, doctor blading, and inkjet printing. In the present study, a novel electrochemical approach has been developed. Layers of semiconducting polymers and fullerene were deposited electrochemically, one on top of another. There were poly(3,4-ethylenedioxythiophene), (PEDOT) hole extraction layer, followed by an intrinsic photoactive layer of a polythiophene derivative and fullerene.;PEDOT was deposited on an ITO surface by cyclic voltammetry from mixed toluene/acetonitrile solvent. The thickness and oxidation state of the layer were monitored by UV-Vis-NIR spectroscopy as well as grazing angle FTIR (GA-FTIR) spectroscopy. The morphology had fibrillar character with roughness and porosity dependent on the thickness of the layer. PEDOT was incorporated into an organic photovoltaic cell as a hole extraction layer with a spin-coated P3HT-PCBM intrinsic layer without further annealing. The cell's performance was found to be effected by the morphology of the PEDOT layer. A fully doped PEDOT layer of moderate thickness was found to have the highest efficiency, demonstrating an open circuit voltage (Voc) of 0.48 V, a short circuit current (Isc) of 5.1 mA/cm2, a fill factor (FF) of 0.46, and an overall efficiency (epsilon) of 1.1 %.;Alternately, the PEDOT layer was deposited from aqueous solution in the presence of various solubilizing agents. A systematic study involving a large number of solubilizers was conducted. It was found that the nature of the solubilizing agent has a drastic effect on the polymerization conditions. The anionic solubilizing agents decreased the polymerization potential and eliminated the induction period of the polymerization. As a result, PEDOT layers with longer conjugation length, higher conductivity and transparency were deposited. The layers were incorporated into the OPVd and efficiencies close to the PEDOT layers deposited from the organic solvent have been reported. The cationic surfactant increased the polymerization potential by 0.21 V and a significant induction period of the polymerization was observed.;As a continuation to the electrochemical deposition of PEDOT layers, fabrication of the polymer solar cells by through the exclusive use of electrochemical depositions was accomplished. Poly(thieno[3,2-b]thiophene) and fullerene were codeposited by cyclic voltammetry from the solution containing corresponding monomers. The composition could be altered by changing its potential range and was monitored by UV-Vis-NIR spectroscopy. Morphology and phase separation were studied by AFM, revealing the formation of bulk heterojuctions. For the device fabrication, the codeposition onto electropolymerized PEDOT layer was achieved without destructive interference. Voc of 0.3 V and Jsc of 35 microA/cm2 were measured under standard AM 1.5 conditions.;Another approach was to build a polymer solar cell by three-layer deposition of poly(3,4-ethylenedioxythiophene)/poly(2,2'-bithiophene)/fullerene (PEDOT/PBT/C60). Electropolymerization of 2,2'-bithiophene was conducted on top of the electrodeposited p-doped PEDOT layer. Fullerene was deposited as a third layer after initiating n-doping of the polymers. Composition and oxidation states of the polymers were monitored by UV-Vis-NIR spectroscopy. Morphological changes were followed with Atomic Force Microscopy (ATM), revealing rough nanostructures in the layers. The composition and performance of the solar cells were compared to the cells fabricated using the conventional spin-coating technique. A Photoresponse with a maximum Voc of 0.47 V and highest Jsc of 0.55 mA/cm 2 was measured. (Abstract shortened by UMI.)... |
