Fast Inline Roll-to-Roll Printing for Indium-Tin-Oxide-Free Polymer Solar Cells Using Automatic Registration

Fast inline roll-to-roll printing and coating on polyethylene terephthalate (PET) and barrier foil was demonstrated under ambient conditions at web speeds of 10 mmin(-1) for the manufacture of indium-tin-oxide-free (ITO-free) polymer solar cells comprising a 6-layer stack: silver-grid/PEDOT:PSS/ZnO/P3HT:PCBM/PEDOT:PSS/silver-grid. The first and second layers were printed at the same time using inline processing at a web speed of 10 mmin(-1) where flexographic printing of a hexagonal silver grid comprises the first layer followed by rotary-screen printing of a PEDOT:PSS electrode as the second layer. The third and fourth layers were slot-die coated at the same time again using inline processing at a web speed of 10 mmin(-1) of firstly zinc oxide as the electron transport layer followed by P3HT:PCBM as the active layer. The first three layers (silver-grid/PEDOT:PSS/ZnO) comprise a generally applicable ITO-free, semitransparent, electron-selective front electrode for inverted polymer solar cells. This electrode shows a low sheet resistance (similar to 10 Omega/square) and good optical transmission in the visible range (similar to 60%). The solar cell stack was completed by rotary-screen printing of a hole-collecting PEDOT: PSS layer at 2 mmin(-1) and a comb-patterned silver-grid back electrode at the same speed. The solar cells were post processed by using fast roll-to-roll switching to a functional state.