Influence of the density of states on the open-circuit voltage in small-molecule solar cells

• Bilayer organic solar cells based on tetraphenyldibenzoperiflanthene and fullerene C70.
• Estimation of density of states from electrical measurements of OTFT.
• Influence of density of states on open circuit voltage.
• Organic p–i–n solar cell fabricated with a power conversion efficiency of almost 4%.

Open-circuit voltages are strongly dependent on the density-of-states in solar cells based on disordered semiconductors. In this work, organic solar cells based on tetraphenyldibenzoperiflanthene and fullerene C70 with a bilayer structure were fabricated to investigate the variation in the density-of-states with the substrate temperature during deposition of the donor. The maximum open circuit voltage was reached at a substrate temperature of 60 °C. Organic thin-film transistors were also fabricated to study their electrical properties, such as the mobility and the density-of-states. Finally, an organic solar cell with p–i–n structure was fabricated at the optimized substrate temperature, and a power conversion efficiency of almost 4% was obtained.