Solvent Effects
Conditions for spin coating and evaporation affect device efficiency. Solvent and additives influence the donor-acceptor morphology. Additives slow down evaporation, leading to more crystalline polymers and thus improved hole conductivities and efficiencies. Typical additives include 1,8-octanedithiol, ortho-dichlorobenzene, 1,8-diiodooctane (DIO), and nitrobenzene. The effect of the DIO was attributed to the selective solubilization of the PCBM component. Additives can also lead to big increases in efficiency for polymers. For HXS-1/PCBM solar cells, the effect was also correlated with charge generation, transport and shelf-stability. Other polymers such as PTTBO also benefit significantly from DIO, achieving PCE values of more than 5% from around 3.7% without the additive.
Small differences in polymer structure can also lead to significant changes in crystal packing which inevitably affect device morphology. In the case of PCPDTBT Vs PSBTBT, there is a significant difference caused by the difference in bridging atom between the two polymers (C vs. Si) which implies that better morphologies are achievable with the PCPDTBT:PCBM solar cells containing additives as opposed to the Si system which achieves good morphologies without any help from additional substances.
Read more about this topic: Polymer Solar Cell
Famous quotes containing the words solvent and/or effects:
“Analysis as an instrument of enlightenment and civilization is good, in so far as it shatters absurd convictions, acts as a solvent upon natural prejudices, and undermines authority; good, in other words, in that it sets free, refines, humanizes, makes slaves ripe for freedom. But it is bad, very bad, in so far as it stands in the way of action, cannot shape the vital forces, maims life at its roots. Analysis can be a very unappetizing affair, as much so as death.”
—Thomas Mann (1875–1955)
“The machines that are first invented to perform any particular movement are always the most complex, and succeeding artists generally discover that, with fewer wheels, with fewer principles of motion, than had originally been employed, the same effects may be more easily produced. The first systems, in the same manner, are always the most complex.”
—Adam Smith (1723–1790)