Effect of pH-Controlled Dye Solution on Improving the Performance and Stability in Organic Solar Cells

In bulk-heterojunction of organic solar cells (OSCs), the morphology of photoactive layer can be controlled through various chemical and physical treatment methods including alcohol treatment, anti-solvent method, and layer-by-layer deposition technique. In particular, it is meaningful that the appropriate film morphology for better charge generation, transport, and extraction is achieved by a simple and accessible process. Our group recently reported ‘water treatment’ with a small amount of water introduced in the preparation process of the active solution to give a physical impact that induces vortex agitation. In this work, we study the effect of pH-controlled dye solution on enhancing the device performance and stability in OSCs. We employed structure-changeable dye molecules within a variety of pH ranges (1-13) as an additive in the process. This strategy makes it possible to obtain more clear phase separation in the thin films treated under high pH conditions. More crucially, by applying this treatment under the basic condition with NaOH as a pH controller, the chemical reaction between the active solvent and additive was generated, thus resulting in enhanced short circuit current densities and fill factors. As a result, an improved efficiency (13.98%) of the device treated with pH-controlled dye solution was achieved compared with the efficiency (13.35%) of PM6:Y6 cells. All these results demonstrated that the treatment using pH-controlled dye solutions is a feasible and promising strategy to construct efficient and eco-friendly OSCs.