Diindenoperylene (DIP) concentration dependent photovoltaic performance and dielectric properties for mixed heterojunctions

To find some intrinsic relevance between the photovoltaic performance and dielectric properties of diindenoperylene (DIP) mixed heterojunctions (MHJs), this work demonstrates both the photovoltaic performance and dielectric characteristic dependence on the DIP concentration. 5 wt%-DIP MHJ shows relatively higher performance compared to other MHJs with higher DIP ratio over the range of 5 wt%–90 wt%. The dielectric constant of blend layers decreases with the DIP ratio, thus results in larger Coulomb capture radius and exciton binding energy, which suppresses the exciton dissociation in MHJs with high DIP ratio. Then, the dielectric characteristic of capacitance-voltage (C-V) in dark and under illumination as well as of capacitance-frequency (C-f) at dc bias of 1.6 V for the DIP MHJs were measured. The geometric capacitance of the MHJs extracted from the C-V in dark indicates a positive dependence on the DIP concentration. C-V peak height decreases with the DIP concentration from 0 to 60 wt% implies that the hole drift becomes dominated at higher DIP content. The open circuit voltage (V_OC) of all the MHJs shows an identical trend with the normalized built-in potential. In dark condition, depletion width (W) gradually decreases with the DIP concentration from 5 wt% to 60 wt%. W becomes narrower under illumination, ascribed to the increased capacitance from photo-generated charge. The free carrier density (N_D) imposes a negative influence on fill factor of MHJs. The extracted electron mobility by C-f characteristic gradually decreases with the DIP ratio.