Development of non-halogenated binary solvent systems for high performance bulk-heterojunction organic solar cells

• Hansen solubility parameters enable rational selection of candidate solvent mixtures.
• Both PCE and EQE increase with the addition of up to 20% benzaldehyde to p-xylene.
• Device performance from p-xylene-benzaldehyde mixture comparable to dichlorobenzene.

Halogenated solvents such as dichlorobenzene (DCB) are commonly used in the fabrication of bulk-heterojunction (BHJ) organic solar cells. However, most halogenated solvents are very toxic. This report provides a route to eliminate halogenated solvents based on Hansen Solubility Parameters (HSPs) for manufacturing high efficiency BHJ solar cells. The device performances fabricated from several different binary solvent systems were compared to that from DCB. For the investigation of different gel behavior of solvent mixtures, Hansen solubility parameters and viscosity were mainly considered for the selection of binary solvent mixture candidates. Upon the addition of 20 vol.% benzaldehyde (BA) to p-xylene (p-XL), the device performances were improved in power conversion efficiency (PCE) from 3.1% to 3.8% and external quantum efficiency (EQE) from 63% to 70%. The solar cell devices fabricated using p-XL/BA binary solvent mixtures exhibited PCE comparable to that from DCB.

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