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 m min −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 m min −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 m min −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 (∼10 Ω/□) and good optical transmission in the visible range (∼60 %). The solar cell stack was completed by rotary‐screen printing of a hole‐collecting PEDOT:PSS layer at 2 m min −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.