Realizing the ultimate goal of fully solution-processed organic solar cells: a compatible self-sintering method to achieve silver back electrode†
It is commonly believed that the ultimate goal of high throughput production of organic solar cells (OSCs) is the fully solution process in the fabrication. While it is highly desirable to form metal back electrodes to complete OSCs by a solution process instead of high-vacuum evaporation to realize the goal, the complex solvents used in typical metal precursor solutions and the post-treatment required such as high-temperature annealing will easily damage active layers and degrade OSC performances. The power conversion efficiencies (PCE) for evaporation-free OSCs have only reached 8%. Besides, there are limited studies that provide clear evidence to successfully eliminate the solvent issue brought by the directly solution-processed metal back electrode. In this work, we demonstrate a compatible self-sintering approach to connect silver nanoparticles (NPs) into a high-quality back electrode. The as-achieved film exhibits a continuous crystal lattice, high purity, excellent conductivity and smooth morphology. Interestingly, since the self-sintering back electrode process is finished in a short time and uses a chemically compatible solvent, it will not degrade the organic active layer and favors high throughput OSCs fabrication. With the back electrode, the fully solution-processed OSCs achieve a PCE of 9.73% which is the highest reported PCE in evaporation-free OSCs to our best knowledge.