Researchers at the University of Groningen, along with collaborators from other institutions, developed a 2.5% efficient organic plastic solar cell using a conjugated polymer/methanofullerene blend. The efficiency was significantly improved by optimizing the molecular morphology of the blend, which reduced phase segregation and enhanced interactions between polymer chains. This improvement was achieved by using chlorobenzene as a solvent during spin coating, resulting in a more uniform mixture and smoother surface compared to toluene. The resulting solar cell demonstrated a power conversion efficiency of 2.5% under AM1.5 illumination, a threefold increase over previous results. The study highlights the importance of solvent choice in determining the performance of organic photovoltaic devices. The research shows that the mechanical and electrical properties of the photoactive layer can be significantly influenced by casting conditions. The chlorobenzene-based device exhibited higher short-circuit current density, fill factor, and overall efficiency due to improved charge carrier mobility and better interfacial contact with the cathode. The results indicate that organic photovoltaic devices can be a viable technology for future power generation, although further work is needed to improve open-circuit voltage and spectral response to match inorganic solar cells. The study was supported by various funding sources and institutions, including the Christian Doppler Society and the Austrian Science Fund.Researchers at the University of Groningen, along with collaborators from other institutions, developed a 2.5% efficient organic plastic solar cell using a conjugated polymer/methanofullerene blend. The efficiency was significantly improved by optimizing the molecular morphology of the blend, which reduced phase segregation and enhanced interactions between polymer chains. This improvement was achieved by using chlorobenzene as a solvent during spin coating, resulting in a more uniform mixture and smoother surface compared to toluene. The resulting solar cell demonstrated a power conversion efficiency of 2.5% under AM1.5 illumination, a threefold increase over previous results. The study highlights the importance of solvent choice in determining the performance of organic photovoltaic devices. The research shows that the mechanical and electrical properties of the photoactive layer can be significantly influenced by casting conditions. The chlorobenzene-based device exhibited higher short-circuit current density, fill factor, and overall efficiency due to improved charge carrier mobility and better interfacial contact with the cathode. The results indicate that organic photovoltaic devices can be a viable technology for future power generation, although further work is needed to improve open-circuit voltage and spectral response to match inorganic solar cells. The study was supported by various funding sources and institutions, including the Christian Doppler Society and the Austrian Science Fund.