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3.4. WP 4 - Lifetime/Modules.
The work is organized into three tasks, dealing with device optimization for selected materials developed in WP1-3, fabrication of 10cm2 modules and testing of device stability under heat and light soaking conditions. We have undertaken some preliminary tests, light soaking (1 sun, ~55 °C), thermal stress test (85 °C / 5% RH), and at the end damp heat test (85 °C / 85 % RH). Initial results from lightsoaking indicated promising stability with only 5% relative loss of performance after ~3400 h.Unfortunately, initial results from thermal stress at 85 °C were less encouraging with efficiencies showing ~60% relative loss of performance after less than 300 h. The degradation mechanism is still not well understood at this point. Several actions are in progress in order toimprove the cell stability at high temperature (>80 °C). Our preliminary damp heat testing
showed mixed results. A combination of materials enabled us to obtain good results at
temperatures up to 75 °C without major degradation and loss of performance. However, the
same test performed at 85 °C permanently damage the cells due to sealing failure and other degradation mechanisms seen on the thermal stress long term testing. New encapsulation methods were used and enabled us to prevent cells from delaminating, and performance loss after testing was reduced (~15-20% loss). At high temperature (>70 °C), it is important to use Bynel® instead of Surlyn®, as Bynel® has a higher melting point, as well as to employ a higher boiling point solvent containing electrolyte (HBS). Experiments are now in progress to assess several combinations of sealing materials and encapsulation methods to overcome the delamination problem and further reduce performance loss at high temperature humidity. Once the degradation issues at the macro scale are overcome, it will enable us to fabricate robust DSC cells and focus on understanding the failure mechanisms at the molecular level.
As an additional work, a strong collaboration has been set-up within the EU-India joint
consortia involving DSL and CNR from the EU side and IICT from the India side, to investigate the to plan durability assessment of IICT’s Y1 dye, which is of commercial interest to Dyesol, and to simultaneously carry out modelling to understand the experimental results and facilitate future predictions of material and device characteristics. Y1 and Y2 dyes from IICT have been shipped to DSL and CNR has calculated the binding energies of these dyes against the Black Dye on TiO2. This topic will be the subject of an EU-India joint publication. In order to “improve temporal stability of 1cm2 cells by 15% over state of the art” according to standard test IEC 61646, we focused our work on the two main tests, i.e. light soaking (1 sun,~55°C) and damp heat test (85°C/85% RH), and several materials (dyes, electrolytes, seals…)were tested. All the results are obtained for standard 8.8x11 mm2 cells (0.88 cm2), which are the standard Dyesol test cells. These are small elements extracted directly from the geometries of larger tiles, so the results can be safely scaled to larger dimensions.Results from light soaking indicated good stability up to ~8000h, with only 8% relative loss of performance. A 19% performance drop after ~11000h was however also observed. We were able to get good results also at the damp heat test, with only a 5% loss of efficiency (at 1 sun) after ~1900h, using cells prepared with 18NR-AO TiO2 paste,TiCl4 OL, Z907 dye, Bynel® 80 μm and HBS-based electrolyte. An epoxy secondary sealing was also applied. Cells were further sealed in a metal-polymer pouch. Encouraging results were obtained for heat test (85°C, dry atmosphere) with an efficiency loss of only 3.2% after 1000h (at ⅓ sun) with the Z907 dye,Surlyn® 50 μm, HBS-2-BI electrolyte and epoxy secondary seal.
Our new device fabrication setup enables us to prepare robust cells that meet the requirements for the standard test IEC 61646. We have seen the positive effect of under and over-layer on cell performances and stability of the seals; we have optimised the epoxy secondary seal and started to investigate the use of a very promising metal/polymer pouch as tertiary seal. Stability assessment of the dyes synthesized in India was performed by considering N749-Y1(from IICT-Hyderabad) cocktails. These DSSCs show much higher efficiencies compared to N749 or Y1 alone (~+16%) and also show also a good stability after ~2000h of long-term light soaking test, with no loss of performance.
Additional stability data (albeit on smaller cells) were gathered for the new MC112 ruthenium dye, synthesized by IICT-India and reported in WP1, for which we got essentially no efficiency decrease after 1000h of long-term light soaking.
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