A bottom-up understanding of the ligand-dominated formation of metallic nanoparticle electrodes with high broadband reflectance for enabling fully solution-processed large-area organic solar cells

Solution-processed top electrodes using metallic nanoparticles have great potential in the high-throughput large-scale industrialization of organic solar cells (OSCs). To overcome poor reflectance, severe conditions of post-treatments, and unclear bottom-up formation mechanisms from nanoscale materials to bulk electrode films, we propose a compact-packing-enabled fabrication approach for stacking and then sintering metallic nanoparticles to become very efficient top electrodes with high conductivity and high broadband reflectance. We establish the formation mechanism in which spray-coated silver nanoparticle (AgNP) electrodes ligated by gallic acid (GA) form well-dispersed compactly packed structures during the stacking. Featuring the self-packing ability of AgNPs and a much higher space proportion of silver, GA-assisted AgNPs with a uniform distribution of particle size and superior storage stability form high-quality AgNP films in low-temperature sintering. Finally, attributing to the superior electrical and optical properties, and facile post-treatment of electrodes, the fully solution-processed OSCs with the GA-assisted AgNP electrodes achieve a record high efficiency of 14.69% for large-area devices (& GE;1 cm(2)).