Performances and impedance spectroscopy of Small-molecule bulk heterojunction solar cells based on PtOEP: PCBM

Small-molecule bulk heterojunction (SBHJ) solar cells based on platinum octaethylporphyrin (PtOEP) as donor material and phenyl-C61-butyric acid methyl ester (PCBM) as the acceptor were fabricated using spin coating techniques with weight ratios from 1:0.1 to 1:9. The formation of charge transfer complex CTC in the PtOEP: PCBM blend was specified from the redshift of the PtOEP absorption peak after blending with PCBM. The photovoltaic performance for PtOEP: PCBM blends were investigated using the external quantum efficiency (EQE) besides the current density-voltage (J-V) characteristics under illumination 100 mW/cm(2) (AM1.5G). The BHJ solar cell with PtOEP: PCBM ratio of 1: 9 exhibited the best performance. The impedance spectroscopy (IS) was examined in the frequency range from 25 Hz to 1 MHz. The equivalent circuit model was evaluated in details to evaluate the impedance spectroscopy parameters. Dielectric constant epsilon', dielectric loss epsilon and dielectric modulus were included and discussed in terms of dielectric polarization processes. Dielectric modulus displays the non-Debye relaxation in PtOEP: PCBM BHJ solar cells.