High performance bulk-heterojunction organic solar cells fabricated with non-halogenated solvent processing

High efficiency bulk heterojunction (BHJ) organic solar cells based upon poly(3-hexylthiophene) (P3HT)-[6,6]-phenyl-C61-butyric acid methyl ester (PCBM) are typically solution processed using halogenated solvents like dichlorobenzene (DCB). In this report, we tune the quality of solvent systems using more environmentally friendly, halogen-free solvents to mimic that of DCB based on Hansen solubility parameters (HSPs). A mixture of acetophenone (AP) and mesitylene (MS) can nearly match the HSPs for DCB. Solar cells fabricated using this solvent mixture can exhibit power conversion efficiency (PCE) comparable to that from DCB with a similar surface morphology. It is critical to control the drying process in the mixed solvent system due to significant volatility difference between AP and MS in order to achieve comparable morphology and PCE. This report illustrates a route to fabricate high efficiency BHJ solar cells from halogen-free solvent systems that could eliminate potential hurdles for manufacturing scale-up of organic BHJ solar cells.

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► Hansen solubility parameters enable rational selection of candidate solvent mixtures.
► An improvement of PCE from 1.6% to 3.4% and EQE from 35% to 69% is obtained by adding 20 vol.% acetophenone to mesitylene.
► The performance of device fabricated with 80–20 vol.% mesitylene-acetophenone mixture is comparable to similar device fabricated with dichlorobenzene.