1 research outputs found
Unraveling the Fundamental Mechanisms of Solvent-Additive-Induced Optimization of Power Conversion Efficiencies in Organic Photovoltaic Devices
The
realization of controllable morphologies of bulk heterojunctions
(BHJ) in organic photovoltaics (OPVs) is one of the key factors enabling
high-efficiency devices. We provide new insights into the fundamental
mechanisms essential for the optimization of power conversion efficiencies
(PCEs) with additive processing to PBDTTT-CF:PC<sub>71</sub>BM system.
We have studied the underlying mechanisms by monitoring the 3D nanostructural
modifications in BHJs and correlated the modifications with the optical
analysis and theoretical modeling of charge transport. Our results
demonstrate profound effects of diiodooctane (DIO) on morphology and
charge transport in the active layers. For small amounts of DIO (<3
vol %), DIO promotes the formation of a well-mixed donor–acceptor
compact film and augments charge transfer and PCE. In contrast, for
large amounts of DIO (>3 vol %), DIO facilitates a loosely packed
mixed morphology with large clusters of PC<sub>71</sub>BM, leading
to deterioration in PCE. Theoretical modeling of charge transport
reveals that DIO increases the mobility of electrons and holes (the
charge carriers) by affecting the energetic disorder and electric
field dependence of the mobility. Our findings show the implications
of phase separation and carrier transport pathways to achieve optimal
device performances