Scalability and stability of very thin, roll-to-roll processed, large area, indium-tin-oxide free polymer solar cell modules

Abstract

Polymer solar cell modules were prepared directly on thin flexible barrier polyethylene terephthalate foil. The performance of the modules was found to be scalable from a single cell with an area of 6 cm² to modules with a total area of up to 186 cm². The substrate thickness was also explored and the performance was found to be independent of thickness in the range of 20–130 μm. The thinner substrates were found to present some challenge regarding handling but were not limited in performance. Large area modules on a substrate thickness of 45 μm were finally prepared by full roll-to-roll processing employing P3HT:PCBM as the active material and were found to exhibit a total area efficiency of >1% (1000 W/m^-2; AM1.5G) with a typical active-area efficiency in the 1.5–1.6% for total module area of >110 cm² due to high fill factors in excess of 50%. The modules were also found to have an active-area efficiency of >1% under low light levels (∼100 W m^-2). The modules were then subjected to extensive stability testing for a minimum of 1000 h employing several ISOS protocols. The modules presented higher than 80% of the initial performance (T80) in the dark (ISOS-D-1), in dark under elevated temperature of 65 °C (ISOS-D-2), under low light (ISOS-LL), under full sunlight (ISOS-L-2), and under outdoor testing (ISOS-O), which was conducted in two locations in India and Denmark. We estimate maximum T80 for those tests to be 2800, 5000, 1300, 1000, and 3500 h respectively. The modules showed significant sensitivity to high humidity and had low values for T80 for dark storage tests at 50 °C/85%RH (ISOS-D-3) and accelerated operation conditions with 0.7 sun/65 °C/50%RH (ISOS-L-3). We found the modules to be particularly suited for information and communications technology (ICT) and mobile applications where low humidity (<50%) and lower temperatures (<65 °C) can be anticipated and we estimate operational lifetimes in excess of 1 year.