Isoindigo-based polymer solar cells with high open circuit voltages up to 1.01 V

• Isoindigo-based copolymers containing nonfluorinated (PIIDBT) and fluorinated bithiophene moieties (PIIDFBT) were synthesized.
• The HOMO of fluorinated PIIDFBT is deeper than that of nonfluorinated PIIDBT.
• The PIIDFBT-based device exhibited a high Voc of 1.01 V.
• The PIIDFBT-based solar cells with PC61BM exhibited a high power conversion efficiency of 6.21%.

Isoindigo-based copolymers containing non-fluorinated (PIIDBT) and fluorinated bithiophene moieties (PIIDFBT) were synthesized. The replacement of hydrogen atoms with electronegative fluorine atom attained the intramolecular noncovalent interactions in conjugated polymer structure employing the concept of conformational locks. Furthermore, the fluorine characteristics as substituent atoms tuned the electron withdrawing ability and made the HOMO energy levels of fluorinated moieties deeper (−5.79 eV) than that of non-fluorinated polymer (−5.54 eV). As a result, the photovoltaic performance of PIIDFBT was improved by increasing its open circuit voltage (Voc) up to 1.01 V, resulting in a power conversion efficiency of 6.21%. The PIIDFBT with high Voc can be recognized as a promising candidate for both single junction and multi-junction photovoltaics.

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