Insight into the relevance between the photovoltaic performance and dielectric properties for tetraphenyldibenzoperiflanthene based mixed heterojunctions

To get insight into the intrinsic relevance between the photovoltaic performance and dielectric properties of tetraphenyldibenzoperiflanthene (DBP) based mixed heterojunctions (MHJs), this work demonstrates the DBP concentration dependent capacitance-voltage (C-V) and impedance spectroscopy characterization in DBP:C60 MHJs. The efficiency gradually decreases with the DBP ratio from 5 wt% to 40 wt%. The dielectric constant (εr) of blend layers indicates no significant difference due to the close εr between C60 and DBP. The open circuit voltage of MHJs and the peak potential of C-V curves keep similar trend changing with the DBP concentration. The depletion width (Wd) linearly increases after doping DBP into C60 matrix, ascribed to the similar εr together with gradually decreased geometric capacitance with the DBP concentration. Density of acceptor impurities (NA) gradually increases with DBP ratio ranging from 5 wt% to 40 wt%, and the bulk carrier accumulation imposes a negative influence on fill factor. The real impedance under illumination depicts an inverse relation with the sequence of short-circuit current of MHJs.