In this paper we report on an attempt to substitute the liquid-electrolyte in Dye Sensitized Solar Cells (LC) by quasi-solid-state constructions (SC) adopting organic/inorganic gels as well as a novel dye comprised of a conjugated polymer covalently linked to a ruthenium complex that can be bound to a TiO2 anatase electrode. Gel polymer electrolytes are prepared by incorporating liquid electrolytes into a polymer matrix such as poly methyl methacrylate (PMMA) using a gelling solvent such as propylene carbonate (PC). Dye Sensitized Solar Cell (DSSC) fabricated using the former gel electrolytes and standard sensitizing dye such as cis-bis(thiocyano) ruthenium(II)-bis-2,2'-bipyridine-4,4'-dicarboxylate (N3) exhibit an encouraging short circuit current densitie (Jsc) of 4.45 mA cm-2 with open circuit voltages (Voc) of 495 mV. In the novel dye the conjugated polymer provides light harvesting and hole conduction while the ruthenium complex binds to the anatase electrode providing efficient charge carrier separation and injection into the anatase electrode.
The synthesis of two new poly(dialkylstilbenevinylene)s obtained through a palladium-catalyzed polymerization with a controlled molecular weight and a terpyridine moiety in the backbone is presented. Assembly using ruthenium complexation led to coordination polymers with a ruthenium complex in the middle. The coordination homo and copolymers were characterized using NMR, UV-vis and were processed into thin films for solar cells applications. The best photoresponse was obtained for the device prepared from the ruthenium homopolymer bearing cyano substitutents with a maximum output power of 0.86 μW cm-2 and a fill factor of 26% under illumination at 1000 W m-2 AM1.5. A blend of this compound with a zinc porphyrin was also investigated and gave a lower performance.
In this paper we would like to address the key role of fabrication in the performance and lifetime of organic photovoltaics. The realization of a complete process line for the construction of large area organic photovoltaics (250 x 400 mm) is described. Among many of the factors that influence organic solar cell lifetime, oxygen and water exposure is the most important. Multiple processes have to be performed under controlled atmosphere and a glove box (or glove boxes), which involves more volume than commercially available glove boxes, needs to house different instruments. The processes housed in the glove boxes were spin coating, evaporation, lamination/sealing and testing, under an inert atmosphere. The main strategy employed multiply connected glove boxes with one load lock. The first glove box was used for spin coating and lamination/sealing, the second will house a screen printer and the third one accommodate an evaporator completely build in house. The evaporator has 2 thermal evaporation sources and 2 e-beams with 4 and 1 crucibles. The process line should allow the entire device realization from substrate coating, to electrode evaporation including the sealing process avoiding air and water exposure. Organic solar cells from small test cells on ITO glass to big modules (250 x 400 mm) of 91 connected cells on ITO PET substrates were fabricated and characterized.
The fabrication of very large area polymer based solar cell modules with a total aperture area of 1000 cm2 has been accomplished. The substrate was polyethyleneterephthalate (PET) foil with a pre-etched pattern of indium-tin-oxide (ITO) anodes. The module was constructed as a matrix of 91 devices comprising 7 rows connected in parallel with each row having 13 individual cells connected in series. The printing of the organic layer employed screen printing of a chlorobenzene solution of the active material that consisted of either poly-1,4-(2-methoxy-5-ethylhexyloxy) phenylenevinylene (MEH-PPV) on its own or a 1:1 mixture (w/w) of MEH-PPV and [6,6]-phenyl-C61-butanoic acid methyl ester (PCBM). Our first results employed e-beam evaporation of the aluminium cathode directly onto the active layer giving devices with very poor performance that was discouragingly lower than expected by about three orders of magnitude. We found that e-beam radiation leads to a much poorer performance and thermal evaporation of the aluminium using a basket heater improved these values by an order of magnitude in efficiency for the geometry ITO/MEH-PPV/C60/Al. Finally the lifetimes (τ1/2) of the modules were established and were found to improve significantly when a sublimed layer of C60 was included between the polymer and the aluminium electrode. Values for the half life of 150 hours were typically obtained. This short lifetime is linked to reaction between the reactive metal electrode (aluminium) and the constituents of the active layer.