Synthesis, optoelectronic and photovoltaic properties of conjugated alternating copolymers incorporating 2,1,3-benzothiadiazole or fluorenone units: a comparative study

A series of p-type alternating copolymers based on oligothiophene and fluorene electron-donating units, and fluorenone or benzothiadiazole electron-withdrawing units was synthesised viaSuzuki coupling reaction. Their optical, electrochemical and photovoltaic properties were investigated in detail allowing rational rules to be drawn on the structure-property relationships. We highlight in this work the crucial role of the side solubilizing groups attached to the polymer backbones that have a significant impact on the morphology of the blends and the solar cell's power conversion efficiency. Devices with an active area of 0.28 cm super(2), based on fluorenone-copolymers and [70]PCBM blends showed V sub(oc) up to 0.95 V and Power Conversion Efficiencies (PCE) up to 1.82% under AM1.5 simulated sunlight (100 mW cm super(-2)) conditions. These values are improved compared to the ones reported to date for this class of materials.