Perylene monoimide based electron acceptors have great properties for use in organic solar cells, like thermal stability, strong absorption and simple synthesis.<br/>However, organic semiconductors typically exhibit low dielectric permittivities. This hinders sufficient exciton dissociation, limiting the theoretically achievable power conversion efficiency. Furthermore, as most active layer materials, they are usually processed from halogenated solvents, thus lowering their attractiveness as green and sustainable technology.<br/>To overcome both limitations at once, this work focuses on introducing polar flexible side-chains to literature-known A-D-A acceptors. The acceptors comprise perylene monoimide as electron withdrawing end groups (A). The electron-rich linker molecules (D), carbazole and fluorene respectively, were modified with oligo ethylene glycol chains or sulfone-ether chains. These chains introduce flexible and polarizable dipoles into the otherwise apolar aromatic molecules, which both improves their solubility in polar non-halogenated solvents, and improves their permittivity via the Clausius-Mossotti relationship.<br/>It was found so far, that the introduction of glycol chains increases the permittivity of both materials by 12 to 18 % compared to their analogues with simple alkyl chains. Furthermore, the solubility of all four acceptors is significantly improved in non-halogenated solvents. This opens the way for both, bulk-heterojunction application with green solvents (xylene, toluene, ethers etc.), or solvent-orthogonal bilayer application of donor and acceptor. The complete results for all four acceptors will be presented.

Tackling both solubility and permittivity improvement by introducing polar side-chains into perylene acceptors

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ACS Fall 2022

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