Functional Ligand-Decorated ZnO Nanoparticles as Cathode Interlayers for Efficient Organic Solar Cells

ZnO as an interlayer plays an important role in organic solar cells (OSCs). There are two kinds of ZnO interlayers, including sol–gel method-obtained interlayers and those obtained using ZnO nanocrystals. While sol–gel ZnO interlayers require thermal treatment, ZnO nanocrystals can generate thin film interlayers without extra treatment. However, ZnO nanocrystals in solution are usually unstable due to strong aggregation, limiting their long-term application. In this work, we reported a method to stabilize ZnO nanocrystals by using a ligand of dimethylglycine. The resulting ZnO–N nanocrystals exhibit high stability in solution, as well as aligned energy levels and efficient charge extraction properties. The application of ZnO–N nanocrystals into OSCs provided a high efficiency of ∼17%, while unmodified ZnO-based solar cells showed a low efficiency of 14.2%.