Exploring the impact of solvent additives on dielectric properties in polymer photovoltaics: A deconvolution and in-depth study of electrical modulus, complex conductivity, and impedance responses

Impedance and dielectric spectroscopy is a well-known technique for characterizing interfaces, especially donor/ receiver interfaces in bulk heterojunction (BHJ) solar cells. This technique was employed to investigate the interface of poly (4,8-bis-alkyloxybenzo(1,2-b:4,5-b0) dithio-phene-2,6-diyl-alt- (alkyl thieno (3,4-b) thiophene2-carboxylate)-2,6-diyl) (PBDTTT-C): PC70BM in bulk heterojunction with DIO as additive. For this reason, a simulation was carried out to generate the complex impedance, modulus, and complex conductivity data based on the electrical parameters extracted from the equivalent circuit. Therefore, a new approach based on the coupling of complex functions such as impedance, modulus, and conductivity has been proposed. In addition, an extrapolation and deconvolution approaches are used to highlight the relaxation processes, the BHJ layer process, the two electrical contacts of the interfaces between PEDOT: PSS/PBDTTT-C: PC70BM and PBDTTT-C: PC70BM/Ca process, and the electrode polarization process. In the next step, the remove the low-frequency process enhances the visibility of other processes, particularly observable in the evolution of the electrical modulus and the conduction parameters associated with each process. In the complex functions, there was a good correlation between all parameters derived from both processes. The characteristics of the conduction processes, such as conductivity values at low and high frequencies and ionic strength were then extracted. All these parameters were evaluated and discussed as a function of the thickness of the active layer. Finally, we demonstrate that the electrical modulus and complex conductivity can be perfect tools to characterize the donor/acceptor interfaces.