Impact Deposition of a Single Droplet of Low-Melting-Point Alloy as the Top Electrode for Organic Photovoltaics.

Top electrodes of organic photovoltaics (OPVs) are usually thermally evaporated in the vacuum, which is non-continuous and time-consuming and has been the bottleneck for the OPV fabrication process. Printable top electrodes that are free of vacuum, high temperature, and solvents will make OPVs more attractive. Low-melting-point alloys (LMPAs) are promising candidates for printable OPV electrodes thanks to the merits of matching work functions, high electron conductivity, high environment stability, and no need for post-treatment. Here, LMPA electrodes are directly deposited on OPVs by simply falling a single LMPA droplet onto the substrate. The LMPA droplet spreads to form a thin film with a smooth interface intimately contacting the substrate. The electrode area can be tailored by adjusting the droplet diameter or the Weber number, which is the ratio of inertia to surface tension. The interface morphology is mainly affected by the contact temperature. The degree of oxidation and charges on the droplet can also influence the electrode area and interface morphology. OPVs with droplet-impacted LMPA electrodes exhibit power conversion efficiencies of up to 16.17%. This work demonstrates the potential of single-droplet impact deposition as a simple method for printing OPV electrodes for scalable manufacturing.