Printing of Low-Melting-Point Alloy as Top Electrode for Organic Solar Cells

The top electrodes of organic solar cells (OSCs) are usually deposited by thermal evaporation in vacuum, which has become the major obstacle toward fully-printed OSCs. The vacuum-free printed top electrodes are highly desirable for the continuous production of OSCs. Here, the printing of low-melting-point alloy (LMPA) as cathodes in OSCs based on the D18:Y6 system is investigated. The Field's metal (FM) is focused with a melting point of 62 degrees C, which could be printed under moderate temperatures that are harmless to the active layers and solidifies at room temperature. More importantly, FM will not melt by solar radiation under practical scenarios. Direct ink writing is used to print the FM cathodes. Two printing modes are identified: the dragging mode in the far field to obtain rod electrodes, and the shearing mode in the near field to achieve relatively flat lamellas. The correlations between processing parameters and properties of the printed electrodes are elucidated. OSCs with printed FM cathodes exhibit the highest power conversion efficiency of 16.44%. The results demonstrate that this facile and robust direct LMPA writing technique is promising for high-performance fully-printed OSCs.