Electrical impedance studies of optimized standard P3HT:PC70BM organic bulk heterojunctions solar cells

• A typical structure of ITO/PEDOT:PSS/P3HT:PC70BM/Al was fabricated.
• Charge carrier diffusion and recombination have been calculated.
• Built-in potential and acceptor impurities concentrations are calculated.

Charge carrier diffusion and recombination in an absorber blend of poly (3-hexylthiophene) (P3HT) and [6,6]-phenyl C70-butyric acid methyl ester (PCBM) with indium tin oxide (ITO) and aluminum contacts have been analyzed by means of impedance spectroscopy. The capacitance exhibits Mott–Schottky behavior indicating the formation of a Schottky junction (band bending) at the P3HT:PCBM/Al interface. Built-in potential of 0.88 V and acceptor impurities concentrations of 9.3 × 1015 cm3 was calculated through capacitance measurements. Impedance measurement shows, at high frequency, an inclined straight line indicates the inhomogeneous nature of the electrode–organic interface. On the other hand, the arc localized at low-frequency is attributed to recombination in the photoactive blend. Global mobility is in the range of 1.1–1.4 × 10−3 cm2 V−1 s−1, which is slightly higher as compared to the literature.