Synergistic
Effects of Binary-Solvent Annealing for Efficient Polymer–Fullerene
Bulk Heterojunction Solar Cells
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Abstract
Conjugated polymer–fullerene-based
bulk-heterojunction (BHJ) organic solar cells (OSCs) have attracted
tremendous attention over the past two decades because of their potential
to develop low-cost and easy methods to produce energy from light.
The complicated microstructure and morphology with randomly organized
architecture of these polymer–fullerene-based active layers
(ALs) is a key factor that limits photovoltaic performance. In this
study, a binary-solvent annealing (BSA) approach was established to
improve the poly(3-hexylthiophene):indene-C<sub>60</sub> bisadduct-based
AL for efficient BHJ-type OSCs by varying the second solvents with
different boiling points (BP). Thus, we were able to change the evaporation
behavior of cosolvents and consequently obtain the various microstructural
properties of the AL. An in-depth study was conducted on the solvent-evaporation
driven morphology of the active layer under various cosolvent conditions
and its effect on the photovoltaic parameters of OSCs. Under the BSA
processes, we found that the specimens with low-BP second solvents
allows us to observe a more ideal AL for increasing photon absorption
and efficient charge transport and collection at the respective electrodes,
resulting in enhanced PCE of the corresponding OSCs. By contrast,
the specimens with high-BP second solvents exhibit random microstructures,
which are detrimental to charge transport and collection and lead
to diminished PCE of the corresponding OSCs. By appropriately selecting
the composition of a binary solvent, BSA can be employed as an easy
method for the effective manipulation of the microstructures of ALs.
BSA is a promising technique for the performance enhancement of not
only OSCs but also other organic/polymeric-based electronic devices