A fluorinated perylene diimide for polar and non-polar green solvent processed organic photovoltaic cathode interlayers

Abstract

Cathode interlayer materials (CILs) for solution-processed organic photovoltaics (OPVs) serve an instrumental role in mitigating charge extraction challenges to achieve high power conversion efficiencies (PCEs). Critical to the mass commercialization of OPV technologies is the use of green solvents to process the multi-layer devices (including the CIL) via roll-to-roll (R2R) compatible coating methods. To address this we report on a new fluorinated N-annulated 2-ethylhexyl substituted perylene diimide material (F-PDIN-EH) and its use as a CIL in conventional OPV devices processable from non-halogenated and non-aromatic solvents. Solubility measurements reveal enhanced processability from green solvents such as ethyl acetate, 1-butanol, and n-heptane for F-PDIN-EH as compared to non-fluorinated reference compound PDIN-EH. OPVs fabricated under ambient conditions using F-PDIN-EH as the CIL processed from polar solvents butanol and ethyl acetate or the non-polar solvent heptane exhibit similar PCEs of 10%. This is the first report of heptane, a non-polar and moderately green solvent, being used to process a CIL, and thus we further exploited this result and demonstrated the scalable processing of F-PDIN-EH using the roll-to-roll compatible slot-die coating method. OPV devices with slot-die-coated F-PDIN-EH films exhibited performance metrics on par with lab-scale spin-coated devices of the same architecture demonstrating industrial application.