Enhancement of the Power-Conversion Efficiency of Organic Solar Cells via Unveiling an Appropriate Rational Design Strategy in Indacenodithiophene-alt-quinoxaline π-Conjugated Polymers

We report on the photovoltaic parameters, photophysical properties, optoelectronic properties, self-assembly, and morphology variations in a series of high-performance donor-acceptor (D-A) pi-conjugated polymers based on indacenodithiophene and quinoxaline moieties as a function of the number-average molecular weight ((M) over bar (n)), the nature of aryl substituents, and the enlargement of the polymer backbone. One of the most important outcome is that from the three optimization approaches followed to tune the chemical structure toward enhanced photovoltaic performance in bulk heterojunction solar cell devices with the fullerene derivative [6,6]-phenyl-C-71-butyric acid methyl ester as the electron acceptor, the choice of the aryl substituent is the most efficient rational design strategy. Incorporation of thienyl rings as substituents versus phenyl rings accelerates the electron-hole extraction process to the respective electrode, despite the slightly lower recombination lifetime and, thus, improves the electrical performance of the device. Single-junction solar cells based on ThIDT-TQxT feature a maximum power-conversion efficiency of 7.26%. This study provides significant insights toward understanding of the structure-properties-performance relationship for D-A pi-conjugated polymers in solid state, which provide helpful inputs for the design of next-generation polymeric semiconductors for organic solar cells with enhanced performance.