Alternative Projektnummern
(Englisch)
EU project number: JOR3-CT98-0261
Forschungsprogramme
(Englisch)
EU-programme: 4. Frame Research Programme – 5.1 Nonnuclear energies
Kurzbeschreibung
(Englisch)
See abstract
Partner und Internat. Organisationen
(Englisch)
ECN (NL); INAP (D); FMF (D)
Abstract
(Englisch)
The Dye Sensitized Solar Cell (DSC) technology uses the principles of the regenerative photoelectrochemical solar cell: A dye stained nanocristalline titanium oxide (TiO2) electrode deposited on a conductive oxide coated glass forms the photoanode, which faces the platinum coated counter-electrode. The gap between the electrodes is filled with an organic electrolyte containing the redox couple iodide/tri-iodide (I-/I3-) necessary for the charge transport within the cell. A rim sealing encloses the system. The DSC technology could allow a significant cost reduction of solar energy as the materials and processing employed is rather simple and low cost compared to traditional technologies based on silicon.
To be able to commercialize Dye Solar Cells for large area power applications it needs to be clear what module lifetimes and efficiencies can be obtained. Therefore there are two main objectives of this project:
a) To demonstrate that a 10 year outdoors module lifetime is feasible
b) To demonstrate that a module efficiency of 10 % is theoretically feasible
In order to assess the stability, high intensity sulfur lamps and a UV-tester were built and distributed to the project partners, ovens and measurement systems completed the equipment. A particular design of dye solar cells was developed, so called masterplates having each 5 cells 5 x 0.8 cm in size and silver lines to collect the current alongside the cells. For the high efficiency task a modified masterplate design was used with cells only 5 mm wide (2.5 cm2 active area).
The stability results can be summarized as following:
In artificial high intensity irradiation (ca. 2500 W/m2) no degradation in the output power was observed after 8300 hours light exposure (it actually went up by ca. 5 %). When the temperature was elevated to 45°C, the maximal degradation was less than 10 % after 4000 hours at 1000 W/m2 irradiation.
In pure UV irradiation at 10 mW/cm2 intensity (340-390 nm) and ca. 38°C, the stability behavior was strongly depending the electrolyte composition. Best stability was obtained with electrolytes containing magnesium iodide or calcium iodide, with no degradation observed after 3300 hours without any UV-filter. The only drawback of those modified electrolytes is there lower performance (by ca. 30%) compared to the standard electrolyte containing no MgI2 or CaI2.
In thermal testing without light or UV irradiation, the cells remained stable overa period of 2200 hours at 60°C, the performance degraded only marginally, starting from 5.25 % efficiency (measured in artificial calibrated sun at 1000 W/m2) and ending at 5.1 % at the end of the thermal exposure. At 85°C, the output degradation was important with 30% after 875 hours of testing – using glass frit sealed cells.
Outdoors testing showed only minor degradation (ca. 10%) after 9 months outside, resp. no degradation after 12 montrhs for another set of cells (5 % efficient) protected behind a window against direct rain exposure.
Reverse biasing a dye solar cell is not critical on the stability, thus integrated modules are possible without protection diodes on each cell.
Efficiency task.
Only cells larger than 1 cm2 were built. Routine efficiency was 5 % on 4 cm2 sized cells despite low fill-factors of only 0.63-0.65 due to (known) inadequate cell design. The reproducability within a masterplate was ca. 8 % deviation in average on the efficiency. The best efficiency measured was 8.18 % (1000 W/m2 AM1.5 simulated at ISE Freiburg) with a improved masterplate of 2.5 cm2 size. The open-circuit voltage is 0.725 V, short-circuit current density is 15.76 mA/cm2 and the fill-factor was 0.716 for that cell with a white background and mask fitted to the active area of the cell. These good efficiency figures were obtained using industrial glass and a thin platinum layer as a counter-electrode and no anti-reflection coating on the front side.
Summary. Good visible light stability was obtained. UV stable cells are possible with additives in the electrolyte. Thermal stability is fine up to 60°C – securing ca. 5 years lifetime outdoors. Best efficiency is 8 % for 2.5 cm2 sized cell with industrial low cost materials. No intrinsic *show-stopper’ was found for stable and efficient Dye Solar Cells.
The stability has to be improved for 85°C by using improved sealing techniques. Combined tests (e.g. IEC 1646) with light, UV and heat have to be undertaken including thermal cycling prior industrialization of this new solar cell technology. The promising LOTS-DSC results are the basis for new projects based on industrially manufactured DSC cell/modules testing to qualify for IEC 1646.