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.