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Abstract: A roll-to-roll process enabling fabrication of polymer solar cells comprising five layers on flexible substrates is presented. The device geometry is inverted and allow for fabrication on both transparent and non-transparent flexible substrates. The process is illustrated in this work by formation of a bottom electrode comprising silver nanoparticles on a 130 micron thick polyethyleneternaphthalate (PEN) substrate. Subsequently an electron transporting layer of zinc oxide nanoparticles was applied from solution followed by an active layer of P3HT-PCBM and a hole transporting layer of PEDOT:PSS. These first four layers were applied by slot-die coating. The final electrode was applied by screen printing a grid structure that allowed for transmission of 80% of the light. The materials were patterned into stripes allowing for formation of a single cell device and serially connected modules comprising 2, 3 and 8 stripes. All five layers in the device were processed from solution in air and no vacuum steps were employed. An additional advantage is that the use of indium-tin-oxide (ITO) is avoided in this process. The devices were tested under simulated sunlight (1000Wm−2, AM1.5G) and gave a typical performance 0.3% in terms of power conversion efficiency (PCE) for the active layer. The low PCE was due to poor transmission of light through the back electrode. [Copyright &y& Elsevier]

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 6cm2 to modules with a total area of up to 186cm2. The substrate thickness was also explored and the performance was found to be independent of thickness in the range of 20–130μm. 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 45μm 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% (1000W/m−2; AM1.5G) with a typical active-area efficiency in the 1.5–1.6% for total module area of >110cm2 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 (∼100Wm−2). The modules were then subjected to extensive stability testing for a minimum of 1000h 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 3500h 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 oC/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 1year. [Copyright &y& Elsevier]

Abstract: Manufacturing of flexible ITO-free polymer solar cell modules by roll-to-roll methods (R2R) is described. Inverted devices with top illumination were built on a Kapton foil and an Aluminum/Chromium bi-layer system was used as electron contact. The layer structure was Kapton/Al/Cr/P3HT:PCBM/PEDOT:PSS/Ag (printed) and devices were encapsulated. Small area cells (3cm2 active area) were first carefully optimized investigating the influence of a number of discrete parameters on performance. A maximum power conversion efficiency of 1.4% was achieved under 1 sun illumination (AM 1.5G, 1000Wm−2). Optimized lab-scale single devices were then transferred to a full R2R process combining slot-die coating and screen printing. All the layers were processed from solution under ambient conditions. Two different concepts were explored: (i) serially connected stripe modules (to reduce the Ohmic losses) and (ii) monolithic modules (to achieve high geometric fill factor and increase the flexibility of the process). For this second concept, the only layer that needs to be patterned is the silver grid electrode and the grid pattern design can then be readily tuned. As an example, four different patterns were used and the resultant performances compared. Modules comprising 16 serially connected cells gave total area efficiencies up to 0.5% (235cm2 – 1% on the active area) while the best monolithic ones gave 0.35% (100cm2 – 0.4% on the active area). The freshly prepared devices consistently showed an inflection point in the IV curve indicative of a rather poor photovoltaic behavior. Upon light exposure and repeated IV scans the inflection point partially disappeared, and performance significantly increased. [Copyright &y& Elsevier]

Abstract: Tandem solar cells with normal and inverted device geometries were prepared by a solution process. Both device types were based on the use of zinc(II)oxide as the electron transporting layer (ETL). The hole transporting layer (HTL) was either PEDOT:PSS for normal geometry tandem solar cells or vanadium(V)oxide in the case of inverted tandem cells. It was found that the inverted tandem solar cells performed comparable or better than the normal geometry devices, showing that the connection structure of vanadium(V)oxide, Ag nanoparticles and zinc(II)oxide functions both as a good recombination layer, ensuring serial connection, and as a solvent barrier, protecting the first photoactive layer from processing of the second layer. This successfully demonstrates a tandem solar cell fabrication process fully compatible with state-of-the-art solution based automated production procedures. [ABSTRACT FROM AUTHOR]