Programm Photovoltaik Ausgabe 2009 ... - Bundesamt für Energie BFE

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Task 2. Encapsulation of Si-based PV cells
Encapsulation of the c-Si cells by hot pressing of the fluoropolymers films with outstanding transparency
from Solvay-Solexis has been carried out in collaboration between LTC, LPI and Solexis. The
main results are summarized in Table 1. The adhesion of the film on the textured c-Si side was good
and no delamination occurred when the cell broke in bending. Plasma treatment of the fluoropolymers
films enabled the adhesion with silicone adhesive to be slightly improved. On the silver backside of the
cell, the adhesion was rather low. Surface texturing of the films has been further investigated in order
to decrease reflection, by hot embossing on a textured c-Si cell (Figure 2). The effect is very interesting:
efficiency of DSC cells (see task 4) at low incidence is improved by more than 10%, compared to
no encapsulation as shown in Table 1.
Figure 2: Hot embossing of fluoropolymer film replicated from textured c-Si cell.
Table 1: Overview of encapsulation performance
Encapsulation Optical Adhesion
Barrier
material performance performance performance
(Transmittance (Peel force on Si, (WVTR, g/m
@ 254 nm) N/m)
2 Efficiency of Efficiency of
DSC
DSC
/day) @ 0° incidence @ 45° incidence
without - - - 14.5% 10.0%
TFE-PFMVE
50 µm
SiO2 coated
TFE-PFMVE
87.5 % 124-180 ~ 3 14.4% 11.2%
87.5 % 586 ~ 3
(discontinuous SiO2)
- -
Task 3. Development of new polymer-gel electrolytes and hole transport materials for DSC
After successful stability test on flexible dye-sensitized solar cells based on molten salts, LPI improved
the efficiency by introduction of a new high molar extinction coefficient ruthenium complex “K77” and
by tuning the electrolyte. This electrolyte is a low viscosity binary ionic liquids (65% PMII = 1-propyl-3methyl-imidazolium
iodide and 35% EMIB(CN)4= 1-ethyl-3methyl-imidazolium tetracyanoborate). A
photovoltaic conversion efficiency of 7.6% was obtained under simulated sunlight AM 1.5 irradiation in
glass/glass device. The cell shows good stability at 80°C in dark (Figure 3) as well under illumination
at 60°C during 1000h accelerated tests. Using a low viscosity ionic liquid and new dye C101 (see Fig.
4) a 5.5% efficiency was obtained for a flexible cell (PEN/Ti system) at 0.5 Sun and 5.2 % at 1 Sun
irradiation (backside). Figure 5 explain the relative drop of efficiency of electrolyte based DSC and
show the comparison between c-Si and DSC-cells under various 1.5 AM illumination. A new concept
of using eutectic mixtures of molten salts as redox electrolytes was proposed by LPI. Employing a
novel ternary eutectic melt in conjunction with a nanocrystalline titania film and the amphiphilic heteroleptic
ruthenium complex Z907Na as sensitizer an excellent stability and an unprecedented efficiency
of 8.2% (lab scale glass/glass device) under air mass 1.5 global (AM 1.5G) illumination were obtained.
Our results are of great importance to realize large-scale outdoor applications of mesoscopic dyesensitized
solar cells.
Ultralight Photovoltaic Structures, Y. Leterrier, EPFL
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