Thickness dependence of organic photodetector bandwidth

Organic bulk heterojunction photodiodes based on a blend of poly(3-hexylthiophene):1-(3-methoxycarbonyl)-propyl-1-1-phenyl-(6, 6)C61 (P3HT:PCBM) have been fabricated with different active layer thicknesses. Current-voltage characteristics and cut-off frequency were measured under Green-LED illumination. Impedance measurements were performed and a simple equivalent circuit was used to fit the resulting Cole-cole diagram. Parameters obtained from the fit were used to estimate the theoretical photodetector cut-off frequency and compared to the experimental one. The material dielectric constant was estimated using the capacitance obtained from the impedance fit.