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29th European Photovoltaic Solar Energy Conference and Exhibition; 1539-1541, Upon ageing of ionic liquid based dye-sensitized solar cells (DSSCs) formation of iodine containing crystals may happen. Herein we show how these crystals can reversibly change in size and how this affects the cell performance if the cells are (i) stored in the dark at room temperature, (ii) exposed to heat treatment at 80 °C and exposed to (iii) reverse or (iv) forward bias current treatment. Crystal change in size was tracked using electroluminescence, while we used current-voltage characterization to determine cell performance. Results reveal the growth of the crystals when the cells were stored in the dark at room temperature while a heat treatment dissolves the crystals. The growth of the crystals is associated with a loss of the I3– ions in the electrolyte which decrease the short-circuit current and increase the open-circuit voltage.

28th European Photovoltaic Solar Energy Conference and Exhibition; 2740-2744, A plasmonic effect of silver nanoparticles in dye-sensitized solar cells (DSSCs) is reported. An isopropanol solution of silver nitrate has been used for dip-coating of TiO2 layers. The Ag nanoparticles (NPs) throughout the active layer have been formed after a heat treatment above 100 °C. Absorption measurements, current-voltage characteristics, external quantum efficiency and the amount of adsorbed dye have been applied to examine the plasmonic effect. Firstly, the 220 °C has been determined as the optimal heat treatment temperature of the TiO2-Ag layers, resulting in the most intensive absorption enhancement and it was used for the preparation of the DSSCs. The I-V characterization of the DSSCs revealed an increase of the short circuit current in the presence of Ag nanoparticles, although the amount of the adsorbed dye decreased. These results confirm performance enhancement related to the plasmonic effect. However neither a thin sol-gel TiO2 layer or a poly(4-vinylpyridine) shells could provide effective protection for a long term stability of the Ag nanoparticles against the corrosion of I3 -/I- based electrolyte.

27th European Photovoltaic Solar Energy Conference and Exhibition; 2897-2902, Ionic liquid based dye-sensitized solar cells (DSSCs) were exposed to 606 kWh/m2 of outdoor irradiance (approximately four months) on faculty’s roof in Ljubljana at short circuit, open circuit, and quasi maximum power point regime. Before, in the middle and after aging the current-voltage characteristics were measured indoor at standard test conditions. Additionally, the electroluminescence and transmittance imaging were used to study local defects. Results of indoor measurements revealed that regardless on the operating regime during ageing, the open circuit voltage of all DSSCs decreases. The JSC of the DSSCs aged under short circuit regime decreases significantly while it is fairly stable when the DSSCs were aged under open circuit and especially under quasi maximum power point regime. Electroluminescence and optical images change upon ageing however a formation of any specific local defect could not be attributed to specific operating regime.

25th European Photovoltaic Solar Energy Conference and Exhibition / 5th World Conference on Photovoltaic Energy Conversion, 6-10 September 2010, Valencia, Spain; 794-797, Dye-sensitized solar cells (DSSC) based on nanocrystalline TiO2 films have attracted much attention as a potential low-cost alternative for commercial solar cells. Nanostructured TiO2 layers are commonly deposited with screen printing or doctor blade technique. The aim of our study was to apply ink-jet printing for layer deposition since it enables simple multiple depositions of the same pattern or spatial selectivity, therefore each layer in a sequence can easily be made of different pattern. In the study inks based on Pechini method were realized by the optimization of the molar ratio between the precursors in the sols. Ink-jet printed layers were used to assemble DSSCs. The performance of solar cells were evaluated and compared with a standard TiO2 layers deposited with doctor blade technique. Efficiencies up to 4.1 % were achieved when DSSCs with ink-jet printed TiO2 layers were illuminated under STC.

24th European Photovoltaic Solar Energy Conference, 21-25 September 2009, Hamburg, Germany; 583-586, The performance of dye-sensitized solar cells based on different TiO2 layers (the standard TiO2 layer, the TiO2 layer based on Ti-isopropoxide, and the novel TiO2 layer based on Pechini sol-gel paste) has been evaluated under standard test conditions. The lowest efficiency among examined cells was found for the dye-sensitized solar cell assembled with standard TiO2 layer. In order to determine the effective electron lifetime in different TiO2 layers applied the open circuit voltage technique was used. The VOC decays after turning off a steady-state illumination were similar for the standard and the TiO2 layer based on Ti-isopropoxide while much slower for the TiO2 layer based on Pechini sol-gel paste indicating slower recombination rate in this layer. Therefore also the highest effective electron lifetime regardless of the VOC, is measured for the DSSC assembled with the layer based on Pechini sol-gel TiO2 paste.

23rd European Photovoltaic Solar Energy Conference and Exhibition, 1-5 September 2008, Valencia, Spain; 556-562, The performance of dye-sensitized solar cells, based on pure 1-propyl-3-methyl-imidazolium iodide ionic liquid electrolyte with different iodine concentrations has been evaluated under different light intensities (10-100 mW/cm2) and for different cell temperatures (5-55 ºC). At lower cell temperatures a short-circuit current (JSC) may be limited by the diffusion of tri-iodide therefore the JSC increases with increasing temperature, until it reaches a maximum. Further increase in temperature leads to a decreases of the JSC due to more pronounced recombinations. The maximum of JSC shifts to lower cell temperatures by increasing iodine concentration or decreasing light intensity. The open circuit voltage decreases linearly with increasing temperature or quasi proportionally to iodine concentration and increases logarithmically with increasing the light intensity, while the conversion efficiency follows the temperature dependence of JSC.