Isoindigo-based conjugated polymer for high-performance organic solar cell with a high V_OC of 1.06 V as processed from non-halogenated solvent

The fabrication of organic solar cells using non-halogenated solvents have been recently explored in order to replace conventionally used halogenated solvents that cause environmental, health and safety problems. For achieving highly efficient organic solar cells using non-halogenated solvents, conjugated polymer should be designed and developed to afford high solubility in non-halogenated solvent and desirable photovoltaic properties in finally fabricated devices. Here, we demonstrated that an isoindigo-based copolymer, PiI2fT, composed of isoindigo with 2-decyltetradecane and bithiophene with fluorination is a promising polymer for organic solar cells using eco-friendly non-halogenated solvent. We found that the introduction of fluorine atom in conjugated polymer affords improved photophysical properties including intense light absorption, lowering of the highest occupied molecular orbital energy level and increase of dipole moment, while the introduction of bulk alkyl chain in the polymer may enhance the solubility in organic solvents. When solar cells were fabricated from using o-xylene and diphenyl ether as solvent and additive, PiI2fT polymer exhibited a high PCE of 8.80% with an open-circuit voltage of 1.06 V.