Linear and propeller-like fluoro-isoindigo based donor–acceptor small molecules for organic solar cells

• Synthesis of linear and propeller-like fluoro-isoindigo based small molecules.
• Analysis of physicochemical, optoelectronic and charge transport properties.
• Influence of molecular architecture on organic solar cell performance.
• High open-circuit voltage (1.0 V) and power conversion efficiency up to 2.2%.
• Highly oriented fibrils for the propeller-like small molecule film.

Two donor–acceptor type fluoro-isoindigo based small molecule semiconductors are synthesized and their optical, electrochemical, thermal, and charge transport properties are investigated. The two molecular chromophores differ by their architecture, linear (M1) vs propeller-like (M2). Both molecules present a broad absorption in the visible range and a low optical HOMO–LUMO gap (∼1.6 eV). AFM images of solution-processed thin films show that the trigonal molecule M2 forms highly oriented fibrils after a few seconds of solvent vapor annealing. The materials are evaluated as electron donor components in bulk heterojunction organic solar cells using PC61BM as the electron acceptor. The devices based on the propeller-like molecule M2 exhibit a high open-circuit voltage (around 1.0 V) and a power conversion efficiency of 2.23%.

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